ENERGY SOURCES - III :LONG ANSWERS

GIVE ANSWER IN DETAIL

*INDEX-TOPIC SEARCH

1. Explain renewable and nonrenewable sources of energy and mention the advantage of such classification.
   

   ANS:
   

   
   
   • Those sources of energy which will be available as long as the heat from sun reaches the earth are called renewable sources of energy.
   
   
   • The renewable sources are generally pollution-free.
   
   
   • Solar energy, hydel energy, wind energy, tidal energy, etc. are renewable sources of energy.
   
   
   • Those sources of energy whose formation takes millions of years and which are limited in supply are called nonrenewable sources of energy.
   
   
   • Nonrenewable sources create heavy pollution.
   
   
   • Coal, petroleum, natural gas, etc. are nonrenewable sources of energy.
   
   
   • The advantage of such classification of energy sources is that it helps us to decide about the conservation of available energy sources for future generation.
   
   
   • It also helps us in development of alternative sources of energy accelerating the scope for the development of appropriate technology.
   
   

   
   



2. Explain the composition of sun's light.
   

   ANS:
   

   
   
   • Sun's light consists of electromagnetic waves of different wavelengths and reachea the earth in the form of radiation.
   
   
   • The waves having wavelength of 4000 A° to 8000 A° are called visible light because these waves cause sensation in our eyes.
   
   
   • The visible light consists of waves of different colours. The wavelength of violet light is about 4000 A° and that of red light is about 8000 A°.
   
   
   • Our eyes are not sensitive to waves with wavelength less than 4000 A° and greater than 8000 A°.
   
   
   • The radiations with wavelength more than 8000 A° are called infrared rays and those with wavelength less than 4000 A° are called ultraviolet rays.
   
   
   • X-rays and γ-rays are electromagnetic waves having wavelength less than that of ultraviolet rays.
   
   
   • A large part of these radiations is made up of visible light whereas about one-third of the light consists of infrared rays which provide us with heat.
   
   

   
   



3. Write a note on solar cooker.
   

   ANS:
   
   
   

   
   
   • Solar cooker is a device that uses solar energy in the form of heat for cooking food.
   
   
   • As shown in figure, solar cooker consists of a container box whose body is made up of nonconducting plastic or fibrous material and insulated from outside to prevent heat loss.
   
   
   • A plane mirror is fixed on the top of the box inb such a way that it reflects sunrays into the box.
   
   
   • Solar cooker contains small containers painted black externally to absorb heat.
   
   
   • The box is covered with a glass-sheet to retain the heat inside due to greenhouse effect. This heat develops about 100-140°C temperature inside the box within 2-3 hours when placed in sunrays.
   
   
   • This type of cooker can be used to prepare food items like rice, dal, pulses, vegetables,etc.
   
   
   • ADVANTAGES
     
     
     
     1. There is no combustion of fuel.
     
     
     2. Maintenance is negligible.
     
     
     3. It is pollution-free.
     
     
     4. The natural taste of the food is maintained as it conserves all nutrients.
     
     
     5. During the preparation of food no personal attention is needed.
     
     
     
     
   
   
   • LIMITATIONS
     
     
     
     1. Food cannot be cooked on a cloudy day or in absence of direct sunlight
     
     
     2. It takes very long time for cooking.
     
     
   
   

   
   

   
   
4. Write a note on solar water heater.
   

   ANS:
   
   
   

   
   
   • Solar water heater is a device which uses solar energy to heat water.
   
   
   • As shown in figure, a copper pipe with its external surface painted black is fixed in the form of a coil in a box similar to that of a solar cooker. The pipe in coiled form increases the surface area for heating.
   
   
   • The cold water is stored in an overhead reservoir tank kept at a higher level. This tank is connected to another tank kept at a lower level slightly above the heater.
   
   
   • One end of the copper pipe of the solar heater is connected to the bottom of the small tank and the other end is connected about halfway from the top of that tank.
   
   
   • This arrangement creates a pressure difference in the small tank and water keeps on circulating repeatedly through the coil of the heater.
   
   
   • The hot water being lighter than the cold water remains in the upper region of the tank and can be taken out for use as and when needed.
   
   

   
   

   
   
5. Write a note on solar concentrators.
   

   ANS:
   

   
   
   • A solar concentrator is a device that receives energy from the sun on a large area and concentrates it onto a very small area.
   
   
   • The principle of its working is that a parallel beam of light incident on a concave mirror is focussed at the principal focus after reflection.
   
   
   • A much higher temperature is obtained using such heating devices.
   
   
   • A solar concentrator is generally made of a large spherical or parabolic reflector mounted on a stand such that it receives maximum amount of solar radiation. For this we can rotate a reflector in such a way that it faces the sun throughout the day.
   
   
   • A simple device using concentrators can attain the temperature in the range of 180-200°C. Such devices are used domestically to heat water and cook food.
   
   
   • For commercial applications, a large number of small plane mirrors is arranged in such a way that all of them concentrate the solar radiation over a small area. Such solar concentrators are useful in generating electricity.
   
   
   • In a solar tower, a concentrator kept at a height of 50-70 m from the ground is used to vaporise water and the steam rotates the turbines of a generator.
   
   
   • The solar furnace created at Mount Louis in France attains the temperature as high as 3000°C with the help of more than about 3500 small mirrors.
   
   

   
   

   
   
6. Write a note on Solar Cells.
   

   ANS:
   
   
   

   
   
   • Solar cell is a device that converts solar energy directly into electrical energy.
   
   
   • Earlier, it was observed that when solar rays fall on a thin wafer of selenium, electricity is generated.
   
   
   • A solar cell made of selenium wafer converts only 0.7% of solar energy into electrical energy which is a very small output and hence impracticable for generating electricity.
   
   
   • The first solar cell made in 1954 could convert about 1% of incident solar energy into electricity.
   
   
   • Modern solar cells most commonly made from semimetal silicon can have efficiency of upto 25%. Silicon is easily available and is eco-friendly.
   
   
   • A typical solar cell consisting of a 2 x 2 cm square piece of pure silicon can produce about 0.7 watt electricity with about 10% efficiency.
   
   
   • This electricity is quite small and to get large amount of electricity several solarcells are connected together in series. This arrangement is called Solar Panel.
   
   
   • ADVANTAGES:
     
     
     
     1. Solar cells provide eco-friendly environment.
     
     
     2. Solar cells can be used anywhere as a self-generating source of electricity.
     
     
   
   
   • LIMITATIONS:
     
     
     
     1. The availability of the special grade silicon required for making solar cells is very limited.
     
     
     2. The cost of connecting material used in solar panels is very high as it is generally silver.
     
     
     3. The current produced by solar cells is direct current (DC) and it has to be converted to alternating current (AC) for some devices. This involves high cost and loss of efficiency.
     
     
     4. The conventional method of storing solar energy in storage batteries is not efficient enough.
     
     
     
     
   
   
   • USES:
     
     
     
     1. In artificial satellites.
     
     
     2. In radio wireless transmission.
     
     
     3. In TV transmission.
     
     
     4. In traffic signals and research centres.
     
     
     5. In calculators and watches.
     
     
     6. In solar cars.
     
     
     
     
   
   

   
   

   
   
7. Write an explanatory note on WIND ENERGY.
   

   ANS:
   

   
   
   • Sun's energy is the main factor responsible for the movement of air. Moving air is called wind and it possesses kinetic energy.
   
   
   • Windmills, invented 250 years ago by Persians, are once again gaining popularity.
   
   
   • Modern windmills convert wind energy into either mechanical energy or electrical energy.
   
   
   • A windmill consists of a fan-like structure mounted at some height on a strong support. Its blades are so designed that when wind strikes them, a pressure difference is created between them. This difference produces a turning effect and makes them rotate.
   
   
   • The height of the windmill, the number of blades and their shape, etc. are decided on the basis of average wind velocity and local environmental factors.
   
   
   • The rotational motion of the windmill is utilised to obtain mechanical work like in a water-lifting pump.
   
   
   • If a turbine is connected to the windmill, electricity can be generated but the electricity generated by one windmill cannot be used commercially.
   
   
   • To generate a lrage amount of electricity, a wind energy farm is established where there are several windmills erected in a large area.
   
   
   • In Gujarat, wind-energy farms are located at following places : Lamba near Porbandar, Okha, Mandavi and Dhank.
   
   
   • The largest windfarm in India is near Kanyakumari in Tamilnadu and it generates 300 MW electricity.
   
   
   • The greatest advantage of wind-energy farms is that the electricity is generated from a renewable source and it is pollution-free.
   
   
   • LIMITATIONS
     
     
     
     1. Wind energy farms can be established only at places with continuous flow of wind.
     
     
     2. The average wind velocity should be 16 km/h to enable its working.
     
     
     3. It requires a large area of land and cost of installation is very high.
     
     
     4. It creates noise pollution.
     
     
   
   
   

   
   

   
   
8. Write an explanatory note on hydel (hydroelectric) energy.
   

   ANS:
   

   
   
   • The electricity generated by moving the turbines of a generator using the energy of flowing water ( or falling water) is called hydroelectric energy or hydel energy.
   
   
   • During rain or snowfall, the potential energy of water molecules is converted into kinetic energy. When ice at higher altitudes melts, its gravitational potential energy is converted to kinetic energy and it flows as a stream of water or as a river.
   
   
   • If we store rainwaters by constructing a dam, the water has higher potential energy. When this water is allowed to fall from a height, its potential energy is converted to kinetic energy.
   
   
   • This kinetic energy of flowing water can be used to rotate the turbine blades along with the armature of electric generator to produce electricity.
   
   
   • The hydroelectric power station at Ukai on the river Tapi in Gujarat generates 300 MW of electricity. A hydroelectric power station has been constructed on river Narmada at Sardar Sarovar dam.
   
   
   • Mini hydroelectric power plants can be constructed in hilly regions or at small dams if the water falls through the height of at least 10 meters.
   
   
   • ADVANTAGES:
     
     
     
     1. Once completed, the hydroelectric power station needs only maintenance and proper management which is not much costly.
     
     
     2. A dam constructed for hydroelectric power station can also be used for irrigation and it prevents floods.
     
     
   
   
   • LIMITATIONS:
     
     
     
     1. The cost of installation (construction) of a hydroelectric power station is very high.
     
     
     2. The requirement of a large area for constructing the dam leads to destruction of forests and causes a great ecological imbalance.
     
     
   
   

   
   

   
   
9. What is OTEC ? Describe the working of OTEC plants.
   

   ANS:
   
   
   

   
   
   • OTEC stands for Ocean Thermal Energy Conversion process.
   
   
   • Oceanic waters absorb very large amount of solar energy during daytime. This creates sizeable temperature difference between water at the surface and water in depth. This temperature difference can be used to convert thermal energy into electrical energy.
   
   
   • PRINCIPLE: If a source of energy is at higher temperatureand the sink (where unused energy is released) is at lower temperature, then a fraction of the heat energy obtained from the source can be converted to electrical energy by running a turbine.
   
   
   • The hot water at the surface of the ocean works as source and comparatively cold water at the depth acts as the sink.
   
   
   • The temperature difference between these two is used to produce electricity.
   
   
   • A temperature difference of at least 20°C is the primary requirement for OTEC. This difference ois available at the depth of about 700 - 900 m. Such places are found between 20°N and 20°S latitudes where such temperature difference is maintained throughout the year.
   
   
   • The benefit of using ocean thermal energy is that this energy is available round the clock whereas solar energy is available only during the daytime.
   
   

   
   

   
   
10. Explain Tidal Energy OR How can electrical energy be generated using tidal energy of the sea (ocean) ?
    

    ANS:
    

    
    
    • The level of water near the seacoast changes twice a day. This everyday movement of water along the seashore is known as tides. A high tide occurs on every new moon day and on a full moon day. During the tide the water level rises by a few meters.
    
    
    • The energy possessed by the rising and falling water is known as tidal energy.
    
    
    • As shown in the figure, a dam is constructed across a narrow opening of a sea. Due to tide, the water moves in and out through the openings and flows over the turbines fixed inside the walls of the dam. The movement of turbines generates electricity.
    
    
    • Tides are not uniform and the rise and fall of water is not large enough to generate electricity on a large scale. Also, there are a very few sites where we find a narrow opening suitable for a dam.
    
    
    • Wind energy is an indirect form of solar energy. Wind possesses tremendous kinetic energy and causes waves in the oceans. The height of such waves is great when the wind velocity is high. Such waves can be used to generate electricity by rotating turbines using their energy.
    
    
    • The greatest limitation of this method is that the location of turbine and other equipment is in the sea. They require a lot of maintenance and replacement. This makes them costlier.
    
    

    
    

    
    
11. Write a note on Geothermal energy.
    

    ANS:
    

    
    
    • Geothermal energy is the energy obtained from the heat of the earth.
    
    
    • Geothermal energy does note depend directly or indirectly on solar energy.
    
    
    • The interior region of the earth below its crust is very hot and it consists of molten rocks called 'magma'. Magma is in semisolid state.
    
    
    • The geological changes push this semiliquid magma towards upper surface and it gets collected at some depth below the surface of the earth. These places are called 'hot spots'. Hot spots are considered as the source of geothermal energy.
    
    
    • When the underground water comes in contact of such hot spots, it turns into steam which is trapped in the space between rocks and becomes compressed due to high pressure.
    
    
    • This steam can be collected by introducing after drilling holes. These pipes reach upto the depth of hot spots. The steam coming up through the pipes can be used to run turbines.
    
    
    • Sometimes the steam finds its way through the cracks in the crust and comes up to the surface in the form of geysers. The steam from such geysers has the temperature of about 150 -200°C.
    
    
    • Geothermal energy is an ecofriendly source of energy and the cost of electricity generated from it is almost half of that of the electricity generated nusing conventional methods.
    
    
    • ADVANTAGES:
      
      
      
      1. This energy can be used for 24 hours throughout the year.
      
      
      2. The cost of production is comparatively low.
      
      
      3. It is eco-friendly, i.e. pollution-free.
      
      
    
    
    • A large number of geysers is found in USA and New Zealand but we have limited places in India for geothermal energy.
    
    
    • In Gujarat, we have geysers at places like Unai, Tulsi Shyam in Saurashtra, and Lasundra and Tuva villages in Godhra District.
    
    

    
    

    
    
12. Describe with diagram the process of preparation of charcoal.
    

    ANS:
    
    
    

    
    
    • AIM: To obtain charcoal from wood.
    
    
    • APPARATUS-MATERIAL: Hard-glass test tubes, stand, Bunsen burner, bent glass tubes, pieces of wood, water, matchstick, etc.
    
    
    • PROCEDURE: Arrange the apparatus as shown in the figure. Put some pieces of wood in the horizontal glass tube. Take some water in the other (vertical) glass tube. Slowly heat the test tube containing pieces of wood with the help of the burner.
    
    
    • OBSERVATIONS:
      
      
      
      1. A black liquid begins to drip in the test tube containing water and settles at the bottom. This thick black semifluid is tar.
      
      
      2. If a lighted matchstick is brought near the outlet of the bent tube fitted to the test tube containing water, the gas released there starts burning. This is coalgas.
      
      
      3. In the end, a black residue is left in the test tube being heated. This is charcoal.
      
      
    
    

    
    

    
    
13. Write a note on biogas.
    

    ANS:
    
    
    

    
    
    • Biogas is produced by the decay of biomass and it consists of 65-75% methane, 30-40% carbon dioxide as well as traces of H₂,H₂S, and N₂.
    
    
    • Because biogas is generally obtained from the solid wastes of animal dung, sewage, crop residues, agro-wastes and poultry droppings, it is traditionally called 'Gobar gas'.
    
    
    • Methane is an excellent fuel. The calorific value of biogas is 35-40 kJ/g.
    
    
    • Two types of biogas plants are commonly used in India.They are :
      
      
      
      1. Fixed-Dome Type
      
      
      2. Floating Gas-Holder Type
      
      
    
    
    • The floating gas-holder type plants have been prepared by the Khadi and Village Industries Commission (KVIC) and are used where biogas is obtained from the animal dung. It consists of a dome like structure, made of steel, that floats up as the pressure of biogas evolved increases.
    
    
    • The fixed-dome type structure has a longer life. Its dome can be made from bricks. Thus, the cost of the plant is reduced. This type of plant is more suitable for obtaining biogas from human excreta and other bio-wastes.
    
    
    • PROCESS:
      
      
      
      • A slurry of dung, other biowastes and water is prepared in a mixing tank.
      
      
      • This slurry is fed into the digester which is a closed underground tank made of bricks.
      
      
      • The digester is sealed from the top.
      
      
      • The anaerobic micro-organisms decompose the biomass in the digester and produce biogas which is a mixture of fuel gases like methane, hydrogen, hydrogen sulphide with carbon dioxide and nitrogen.
      
      
      • After a few days, sufficient gas is produced which is supplied to the places of use.
      
      
    
    
    • ADVANTAGES:
      
      
      
      1. It can be supplied to the consumers through pipes.
      
      
      2. Its main component methane is an excellent fuel and burns without smoke.
      
      
      3. It does not produce ash during burning.
      
      
      4. It can be used as a fuel for domestic heating, cooking, lighting as well as to generate electricity.
      
      
      5. It can be supplied to industries as a fuel.
      
      
      6. The slurry left behind in the digester serves as an excellent manure for farmers.
      
      
      7. It provides us with a scientific method of disposal of organic wastes.
      
      
    
    

    
    

    
    
14. Explain Hydrogen as a fuel.
    

    ANS:
    

    
    
    • Hydrogen, when burnt in presence of oxygen, produces a lot of heat energy and water with explosion.
      
         H₂ + 1/2 O₂ → H₂O + Heat
      
      Due to its high calorific value it can be considered as an alternative source of energy.
    
    
    • Hydrogen is obtained as a by-product in many industrial processes. It is also produced during electrolysis of water.
    
    
    • ADVANTAGES:
      
      
      
      1. Its combustion produces water. Therefore, it is free from pollution.
      
      
      2. Its calorific value is 150 kJ/g which is the highest among known fuels.
      
      
      3. It is easily available as the main by-product of some industrial processes.
      
      
    
    
    • USES:
      
      
      
      1. For the production of methanol, ammonia and hydrocarbons.
      
      
      2. As a fuel in space-ships.
      
      
      3. As a source of energy in high temperature flames.
      
      
    
    
    • LIMITATION:The combustion of hydrogen is highly explosive in nature. Thus, it cannot be used as a source of energy both for domestic as well as industrial applications.
    
    

    
    

    
    
15. Write a note on Coal.
    

    ANS:
    

    
    
    • Cual is a conventional source of energy.
    
    
    • Coal mainly consists of carbon with traces of other elements like hydrogen, oxygen, nitrogen, phosphorus, pottasium, etc.
    
    
    • It is available as deposits below the surface of the earth.
    
    
    • India's first coal mine was dug in Raniganj of West Bengal in 1854 AD.
    
    
    • Based on the carbon content, coal is classified as peat, lignite, bituminous and anthracite.
    
    
    • Peat contains about 27% of carbon (which is the lowest).
    
    
    • Lignite contains about 28-30% carbon.
    
    
    • Bituminous coal contains about78-87% carbon.
    
    
    • Anthracite contains about 94-98% carbon.
    
    
    • Anthracite is the best quality coal which does not produce any residue(ash) after burning.
    
    
    • As a fuel coal burns in presence of oxygen to form CO₂ and produces a lot of heat.
    
    
    • It is widely used as domestic as well as industrial fuel and for generating electricity in thermal power stations.
    
    
    • Coke (a form of carbon) is produced from coal by its destructive distillation.
    
    
    • Coke is used as a reducing agent in the extraction of metals from their ores and for preparation of steel.
    
    

    
    

    
    
16. Describe fractional distillation of petroleum with neat diagram and write the names of the products obtained.
    

    ANS:
    

    
    
    • Petroleum (crude oil) is a complex mixture of many hydrocarbons. It cannot be used in crude state. Its components are separated by fractional distillation process.
    
    
    • As shown in figure, the fractional distillation tower is about 31 m high cylindrical structure with 3 m diameter. It is made of iron.
    
    
    • It consists of trays made of specially designed bricks. These trays are kept at regular intervals from bottom to the top of the tower. They are porous and have bubble caps.
    
    
    • The crude oil is heated to about 400-430°C temperature before being introduced into the tower from its base.
    
    
    • All the hydrocarbons are vaporised at this temperature and as these vapours rise up, they get cooled down. The component having the highest boiling point gets condensed first and becomes liquid. Similarly all the components condense gradually into liquid form and get collected over different trays kept at different levels.
    
    
    • The residue left as tar and bitumen is collected at the bottom of the tower.
    
    

    
    

    
    
17. Write a descriptory note on the products (components) obtained during fractional distillation of petroleum.
    

    ANS:
    

    
    
    • PETROLEUM GASES:
      
      >
      
      • Petroleum gases are collected at the top as they do not condense.
      
      
      • It is a mixture of hydrocarbons like methane, ethane, propane and butane.
      
      
      • Butane is an easily combustible gas and is a very good domestic fuel.
      
      
      • Butane is converted into liquid under pressure and stored incylinders as LPG (Liquefied Petroleum Gas) to use it as domestic fuel.
      
      
      • When we release the pressure in the cylinder, this liquid butane gets converted into gas and reaches the burner through pipes.
      
      
      • LPG is highly inflammable gas and catches fire immediately.
      
      
      • It is difficult to detect its leakage as it is odourless. To avoid disaster due to leakage a small amount of foul smelling mercaptan is added to it. The smell of mercaptan helps us take precautionary measures to avoid accident.
      
      
    
    
    • PETROL:
      
      
      
      • It is obtained in the temperature range of 40 to 200°C.
      
      
      • Its proportion in petroleum is about 45% and is also known as 'gasoline'.
      
      
      • The hydrocarbon molecules in it contain 5-10 carbon atoms.
      
      
      • Its calorific value is 47 kJ/g.
      
      
      • It is used as a fuel in automobiles.
      
      
    
    
    • KEROSENE:
      
      
      
      • It is obtained in the temperature range of 200-300°C.
      
      
      • The hydrocarbon molecules in it contain 10-14 carbon atoms.
      
      
      • Its calorific value is 48 kJ/g.
      
      
      • It is used domestic fuel for cooking and in lanterns. Highly refined kerosene is used as a fuel in jet planes.
      
      
    
    
    • DIESEL:
      
      
      
      • It is obtained in the temperature range of 300-350°C.
      
      
      • The hydrocarbon molecules in it contain 14-20 carbon atoms.
      
      
      • Its calorific value is 45 kJ/g.
      
      
      • It is used in heavy vehicles like trucks, buses, tractors, railway engines, steamers as well as in water pumps and generators.
      
      
      • It was invented by Rudolph Diesel.
      
      
    
    
    • LUBRICATING OIL:
      
      
      
      • It is obtained in the temperature range of 350-400°C.
      
      
      • The hydrocarbon molecules in it contain more than 20 carbon atoms.
      
      
      • It is used in the preparation of grease and wax.
      
      
    
    
    • PETROLEUM WAX:It is obtained in semifluid state above 400°C and is used in the preparation of candles.
    
    
    • ASPHALT:The thick, black, viscous liquid left as residue is called asphalt(bitumin) and is used in the preparation of roads and as a water repellant.
    
    

    
    

    
    
18. Write a note on Natural Gas.
    

    ANS:
    

    
    
    • Usually natural gas is found with petroleum.
    
    
    • It mainly consists of methane which is a very good fuel along with some hydrogen.
    
    
    • Natural gas has the advantage that it can be transported to both domestic as well as industrial consumers through the pipelines.
    
    
    • It can be compressed to liquid state when it is called Liquefied natural Gas (LNG) or Compressed Natural Gas (CNG) and it can be transported through tankers easily.
    
    
    • Its combustion produces comparatively less pollution as only carbon dioxide and water are formed after combustion.
    
    
    • In India natural gas is found in Khambhat, Tripura, Jaisalmer, Bombay High and KG (Krishna-Godavari) basins. India's reserves of natural gas are estimated to be about 100 billion cubic meter.
    
    
    • In Gujarat, the power station at Dhuvaran uses natural gas to generate electricity.
    
    
    • The uses of natural gas are:
      
      
      
      • As a fuel in industries and power stations.
      
      
      • In the manufacture of artificial fertilisers like ammonia and urea.
      
      
      • As a source of hydrogen gas.
      
      
      • As a source of methane for use as domestic fuel.
      
      
    
    
    

    
    

    
    
19. Write a note on Conditions of Burning.
    

    ANS:Burning or combustion is an exothermic process in which a substance combines with oxygen and a lot of heat is produced. The following are the conditions which must be satisfied for burning to take place.
    
    

    
    
    1. IGNITION TEMPERATURE: Ignition temperature is the minimum temperature to which a substance must be heated in presence of oxygen to start burning. A substance does not burn until it reaches its ignition temperature. Thus, a substance must be heated upto its ignition temperature to start burning.
    
    
    2. OXYGEN: Adequate supply of oxygen is necessary for efficient combustion. If the supply of oxygen is sufficient, the process is called COMPLETE COMBUSTION and if the supply is insuuficient then it is called INCOMPLETE COMBUSTION. During complete combustion the fuel burns with blue flame and maximum amount of heat energy is released. During incomplete combustion, heated unburnt carbon particles give out yellow light and the complete energy of the fuel is not released.
       
       Stoves using kerosene are designed such that they get sufficient oxygen from their surroundings. On the other hand, kerosene lamp or lantern used for light is designed such that it does not get sufficient oxygen and gives yellow light.
    
    
    3. FUEL SUPPLY: For combustion to continue properly, a minimum level of the fuel supply must be maintained.
    
    

    
    

    
    
20. Mention the characteristics of the Ideal Fuel.
    

    ANS:The characteristics of an ideal fuel are:
    

    
    
    • It should be available easily and in enough quantity.
    
    
    • Its ignition temperature should be well above the room temperature and in accordance with the necessity.
    
    
    • It should have high calorific value.
    
    
    • It should burn completely and leave minimum amount of volatile material.
    
    
    • Its storage and transportation should be easy and safe.
    
    
    • It should be economical (less costly).
    
    
    • It should not produce poisonous gases on combustion and thus cause minimum pollution.
    
    

    
    

    
    
21. Describe an experiment to find out calorific value of wax.
    

    ANS:
    

    
    
    • AIM: To determine the calorific value of wax.
    
    
    • APPARATUS & MATERIAL: Beaker, tripod, thermometer, water, candle, etc.
    
    
    • PROCEDURE:Take a candle and record its mass(weight). Take fixed quantity (say, 100g) of water in the beaker and measure its initial temperature. Heat the water with the help of the candle and extinguish the candle after some time when the temperature of water has risen sufficiently. Record the final temperature of water as well as the mass of the extinguished candle.
    
    
    • OBSERVATIONS:
      
      
      
      1. Initial mass of the candle = W₁ gram
      
      
      2. Mass of water = m gram
      
      
      3. Initial temperature of water = t₁ °C
      
      
      4. Final temperature of water = t₂ °C
      
      
      5. Final mass of the candle = W₂ gram
      
      
    
    
    • CALCULATION:
      
      
      
      1. Quantity of wax used = W = W₁ - W₂ gram
      
      
      2. Increase in the temperature of water = t = t₂ - t₁ °C
      
      
      
      
      Now, Heat absorbed by water Q = m x s x t
              [where s is the sp.heat of water]
      
          ∴ Calorific value of wax = Q/W = (m x s x t)/t
    
    
    • CONCLUSION:The calorific value of wax is _______ cal/g.
    
    

    
    

    
    
22. Explain Nuclear Fission.
    

    ANS:
    

    
    
    • During an attempt to produce transuranic elements, Prof. Fermi and his coworkers observed that when neutrons are bombarded on a nucleus, β-particles are emitted.
    
    
    • Hahn and Strassman found that ₉₂U²³⁵ on bombardment by a neutron produces ₅₆Ba¹³⁹ which emits β-radiation and gets converted into ₅₇La¹⁴⁰.
    
    
    • The splitting of a heavy nucleus into daughter elements spontaneously or as a result of bombardment by a neutron is called NUCLEAR FISSION.
    
    
    • There are two categories of nuclear fission:(1) Prompt fission (2) Delayed fission.
    
    
    • If an atom (like uranium) is bombarded by a high-energy neutron, its nucleus splits immediately. This is prompt (rapid) fission.
    
    
    • In delayed (slow) fission, the bombarded neutron is absorbed by the target nucleus (uranium) and excites the nucleus which splits later on.
    
    
    • During nuclear fission, the heavy nucleus obtained after fission has atomic mass 130 - 149 u and the light nucleus has the atomic mass 85 - 104 u.
    
    
    • If the nucleus of a heavy element (or its isotope) splits without being bombarded by any particle, the fission is called 'Spontaneous fission'.
    
    
    • During nuclear fission, some neutrons are released. For example, in the fission of ₉₂U²³⁵, on an average 2 - 3 neutrons are released.
    
    
    • During fission, a large amount of energy is released. Let us take the following example:
      
      ₉₂U²³⁵ + ₀n¹ → ₃₅Mo⁹⁵ + ₅₇La¹³⁹ + 2₀n¹
      
      Here the sum of the atomic masses on the left hand side is
      
      235.124 u + 1.009 u = 236.133 u
      
      and the sum of the atomic masses on the right hand side is
      
      94.946 u + 138.955 u + 2.018 u = 235.919 u
      
      the difference in the total mass of reactants and products is called 'MASS DEFECT'. The mass defect in the above example is
      
      236.133 u - 235.919 u = 0.214 u
      
      This lost mass (mass defect) is converted into energy. According to the Einstein's mass-energy equation when 1 u mass is converted, 931.48 MeV energy is produced.
      
      Thus, in the above example, 0.214 u mass is converted to produce 200 MeV energy which is equivalent to 3.2 x 10^-11 Ws (joule) of energy.
    
    
    
    • The fission of 1 kg of ₉₂U²³⁵ produces 10⁹ W-day or 1000 MW-day energy. If only 30% of this energy is converted into electrical energy, we get 300 MW-day energy for which 2500 tons of coal are needed.
    
    
    • Electrical energy is produced by using chain reaction in which the neutrons produced in previous reaction are used to split uranium nuclei in subsequent steps. This type of fission is carried out in special type of vessels called Nuclear Reactor.
    
    

    
    

    
    
    
23. What is Chain Reaction ? Describe the ideal conditions to support a chain reaction.
    

    ANS:
    
    
    

    
    
    • If in a reaction the products of one step result in producing the subsequent step of the reaction then that reaction is called 'Chain Reaction'.
    
    
    • During the fission of ₉₂U²³⁵, two or three neutrons are released. If the energy of these neutrons is utilised to cause fission of other nuclei, then again two or three neutrons are released per nuclei. Thus, the process of fission continues as chain reaction.
    
    
    • The reaction mentioned above will go beyond control if all the neutrons released in one step are utilised to cause fission in the subsequent step. Because the number of neutrons released will go on increasing, the amount of energy produced will also go on increasing and reach an uncontrollable stage.
    
    
    • The following processes can take place after neutrons are produced in the fission reaction.:
      
      
      1. At least one of the neutrons (released during previous step) hits the other ₉₂U²³⁵ to cause fission to release more neutrons ( & energy).
      
      
      2. The neutrons may be captured by the uranium nucleus (parent nucleus) without fission to take place.
      
      
      3. The neutrons may be captured by the other nucleus (daughter nuclei) either in fission material or in the surrounding containers even without causing fission.
      
      
      4. The neutrons may not interact with one another and the nucleus and may escape from the system.
      
      
    
    
    • The fission reaction would stop if the last three processes dominate. However, the fission reaction will continue if the first process is repeated at least once.
    
    
    • Thus, the ideal condition to support the chain reaction will be to lower the energies of released neutrons to thermal neutron energy range of 0.04 eV.
    
    
    • This can be achieved by using special substances called moderators like graphite and heavy water which take out some of the energy of the neutron.
    
    

    
    

    
    
24. With the help of a neat diagram describe a nuclear reactor.
    

    ANS:
    
    
    

    
    
    • A nuclear reactor is used for generation of electric power, production of fissile materials, nuclear research and for the production of man-made radioactive isotopes.
    
    
    • As shown in figure a nuclear reactor consists of a core of reaction vessel called pressure chamber that can withstand very high pressures.
    
    
    • The core consists of fuel rods (uranium rods) used as the fuel as well as a moderator like heavy water or graphite.
    
    
    • The water is pumped into the pressure chamber to remove the heat generated during fission. This heat converts water into steam.
    
    
    • This steam with high pressure and temperature is used to rotate the turbines of the generator and electric power is generated.
    
    
    • The steam loses its heat in the process and cools down. It is allowed to cool further and the water thus obtained is reused in the process.
    
    
    • The different fractions (products) obtained are : petroleum gases, petrol(gasoline), kerosene, diesel, lubricating oil, petroleum wax, tar, etc.
    
    

    
    

    
    
25. Explain : Nuclear Fusion.
    

    ANS:
    

    
    
    • The process in which two nuclei combine to form a heavy nucleus is called Nuclear Fusion.
    
    
    • For example, two nuclei of heavy hydrogen (deuterium), ₁H² fuse to form one nucleus of helium, ₂He³.
    
    
    • During nuclear fusion, the mass of the products formed is slightly less than the mass of the reactants. This is called 'Mass Defect' and the 'missing mass' is converted into energy according to the Einstein's mass-energy equation, E = mc².
    
    
    • When two deuterium nuclei combine, following two reactions are possible:
      
      ₁H² + ₁H² → ₂He³ + ₀H¹ + 3.3 MeV
      
      ₁H² + ₁H² → ₁H³ + ₁H¹ + 4.0 MeV
    
    
    
    • The main advantage of the above reaction is that we obtain about 33 g of deuterium from 1 cubic meter (1000 lit) of seawater. Thus, seawater contains about 10¹⁵ tons of deuterium.
    
    
    • 1 gallon of deuterium releases energy equivalent to that released by 600 gallons of petrol.
    
    
    • The following reaction involving tritium is possible at low temperature and it gives more energy.
      
      ₁H³ + ₁H² → ₂He⁴ + ₀n¹ + 17.6 MeV
    
    
    
    • The proportion of tritium in seawater is less but we can obtain it by bombarding lithium isotope with a neutron.
      
      ₃Li⁶ + ₀n¹ → ₁H³ + ₂He⁴
      
      ₃Li⁷ + ₀n¹ → ₁H³ + ₂He⁴ + ₀n¹
    
    
    
    • In thermonuclear fusion process, a fusion fuel is heated to 10⁶ K when ionization takes place to form plasma.
    
    
    • Plasma is a mixture of moving charged particles with equal number of negative and positive charges.
    
    
    • It is difficult to control thermonuclear fusion. However, attempta are going on to develop a process of controlled fusion to obtain energy.
    
    
    • Uncontrolled nuclear fusion is used to prepare weapons of mass destruction like hydrogen bomb.
    
    
    • As compared to nuclear fission, the nuclear fusion has following advantages:
      
      
      
      1. Fuel for nuclear fusion is cheap and easily available.
      
      
      2. There is no requirement of disposing off of nuclear wastes.
      
      
      3. It is pollution free.
      
      
    
    

    
    

    
    
26. Write a note on Nuclear Hazards.
    

    ANS:
    

    
    
    • A nuclear blast can cause death of millions of people in a few seconds.
    
    
    • It can damage huge structures like buildings.
    
    
    • Heat produced during such blast can spread into large area destroying life.
    
    
    • There are mainly two types of dangers from nuclear radiation : (1) Pathological danger (2) Genetic danger.
    
    
    • Pathological effects cause diseases like cancer which may prove fatal.
    
    
    • Genetic effects cause damage to the children of next generation in the form of various physical disabilities.
    
    
    • Leakage of radiation from nuclear reactors adversely affect all spheres of the environment.
    
    
    • The accidental leakage from a nuclear reactor in Chernobyl (Ukraine) in 1986 was so serious that about 50 tons of radioactive material had spread over a large area that thousands had died and about 2 lakh people had to be shifted to safer place. The radiation in this explosion was 200 times the radiation spread by the atomic bomb in Hiroshima and Nagasaki.
    
    
    • The disposal of nuclear wastes, rods of nuclear fuel is a great problem as it spreads radiation continuously. Such material is at present buried very deep in the earth where it is unlikely to come in contact of underground water.
    
    

    
    

    
    
27. DISTINGUISH BETWEEN NUCLEAR FISSION AND NUCLEAR FUSION.
    
    ANS:
    
    

ENERGY SOURCES - II :BRIEF ANSWERS

ANSWER IN BRIEF

*INDEX-TOPIC SEARCH

1. 'A very minute part of sun's energy reaches the earth.' Justify giving details.
   

   ANS:
   

   
   
   • Sun is the ultimate source of energy for earth. Tremendous amount of energy is continuously produced in sun due to thermonuclear fusion process and this energy is radiated by the sun into the space.
     
   • The sun releases 3.8 x 10²⁶ joule of heat energy per second in all directions.
     
   • Only 1.7 x 10¹⁷ joule of heat energy per second reaches the surface of the earth which is only 0.000000045792% of sun's energy output.
     
   • Thus, a very minute part of sun's energy reaches the surface of the earth.
     

   
   

   
   
2. Mention two categories of solar appliances with examples.
   

   ANS:Solar appliances are classified into two categories on the basis of principle of their working.
   (1)Devices that convert solar energy into heat energy : for example, solar cooker and solar water heater.
   (2)Devices that convert solar energy into electricity : for example, solar cells.
   

   
   
3. Distinguish between renewable and nonrenewable sources of energy.
   

   ANS:
   

   
   
   
4. How are smokeless chulhas more efficient than the traditional chulhas ?
   

   ANS:Only 8 - 10% of the energy of the fuel(firewood) is used when burnt in traditional chulhas as the supply of oxygen is less. In smokeless chulhas, the fuel gets more oxygen and the efficiency is increased. Moreover, incomplete combustion of fuel in traditional chulhas creates pollution due to smoke.
   

   
   
5. How was petroleum formed ?
   

   ANS:Many aquatic plants and animals were buried down in the earth centuries ago (in fact, millions of years ago). The high temperature and pressure created due to the layers of earth formed above them converted their fossils into petroleum. Usually it is formed under sedimentary rocks and its formation involves complicated reactions.
   

   
   
6. Mention Uses of Natural gas.
   

   ANS:
   
   The uses of natural gas are:
   

   
   
   • As a fuel in industries and power stations.
     
   • In the manufacture of artificial fertilisers like ammonia and urea.
     
   • As a source of hydrogen gas.
     
   • As a source of methane for use as domestic fuel.
     

   
   

   
   
7. Give reason: The calorific value of wood is lower than that of the hydrocarbons.
   

   ANS: The calorific value of hydrogen is the highest. The calorific value of a fuel is higher if its hydrogen content is high. The hydrocarbons are made of carbon and hydrogen only whereas wood is made of carbohydrates. Carbohydrates contain oxygen in addition to carbon and hydrogen. Oxygen does support combustion but it does not burn itself. Therefore, it does not contribute to the energy released. Thus, the calorific value of wood is lower than that of the hydrocarbons.
   

   
   
8. Explain how the energy obtained from nuclear fusion is better than that obtained from fission reactions.
   

   ANS:The energy obtained from nuclear fusion is better than that obtained from fission reactions because of the following advantages of fusion process:
   

   
   
   • The fuel for nuclear fusion is cheaper and easily available.
     
   • There is no requirement of disposing off of the nuclear waste.
     
   • It is comparatively pollution-free.
     

   
   

   
   
9. State the advantages and limitations of a solar cooker.
   

   ANS:Refer to the long answer on Solar cooker.
   

   
   
10. Distinguish between petrol and diesel.
    ANS:
    
11. Distinguish between petrol and kerosene.
    ANS:
    

ENERGY SOURCES - I :MCQs & SHORT ANSWERS

*INDEX-TOPIC SEARCH

MULTIPLE-CHOICE QUESTIONS

SELECT THE CORRECT ALTERNATIVE:

1. _______ is not a fossil fuel.
   
   
   
   1. Coal
   2. Natural gas
   3. Petroleum
   4. Wind energy
   
   
   
   
2. The coal reservoirs are estimated to last for another _______ years.
   
   
   
   1. 50
   2. 100
   3. 250
   4. 500
   
   
   
   
3. ________ reaction is continuously going on in sun.
   
   
   
   1. Thermonuclear fusion
   2. Thermonuclear fission
   3. Thermostatic fusion
   4. Thermostatic fission
   
   
   
   
4. How much energy does sun release in the form of radiation ?
   
   
   
   1. 3.8 x 10²⁴ joule/second
   2. 3.8 x 10²⁶ joule/second
   3. 1.7 x 10¹⁷ joule/second
   4. 1.7 x 10²⁶ joule/second
   
   
   
   
5. How much energy from sun reaches to earth's surface ?
   
   
   
   1. 3.8 x 10²⁴ joule/second
   2. 3.8 x 10²⁶ joule/second
   3. 1.7 x 10¹⁷ joule/second
   4. 1.7 x 10²⁶ joule/second
   
   
   
   
6. The average distance between the sun and the earth is _______.
   
   
   
   1. 1.5 x 10⁵ km
   2. 1.5 x 10⁶ km
   3. 1.5 x 10⁷ km
   4. 1.5 x 10⁸ km
   
   
   
   
7. The value of solar constant is ________.
   
   
   
   1. 1.335 kW/m²
   2. 1.533 kW/m²
   3. 1.358 kW/m²
   4. 1.353 kW/m²
   
   
   
   
8. Approximately ______ of energy striking the outer atmosphere of earth reaches its surface.
   
   
   
   1. 46 %
   2. 47 %
   3. 48 %
   4. 49%
   
   
   
   
9. Of the visible light ______ has the maximum wavelength and ______ has the minimum wavelength.
   
   
   
   1. red, green
   2. red, yellow
   3. red, violet
   4. violet, red
   
   
   
   
10. The wavelength of visible light is ________.
    
    
    
    1. 4 x 10^-7 to 8 x 10^-7 m
    2. 4 x 10^-6 to 8 x 10^-6 m
    3. 4 x 10⁷ to 8 x 10⁷ m
    4. 4 x 10⁶ to 8 x 10⁶ m
    
    
    
    
11. The wavelength of infrared rays is ______.
    
    
    
    1. less than that of red rays
    2. less than that of violet rays
    3. more than that of red rays
    4. more than violet but less than that of red rays
    
    
    
    
12. The wavelength of ______ is less than that of violet rays.
    
    
    
    1. ultraviolet rays
    2. red rays
    3. infrared rays
    4. green rays
    
    
    
    
13. Who used solar energy to run engines using hot air ?
    
    
    
    1. Ericson
    2. Gunter
    3. Thomson
    4. Joule
    
    
    
    
14. We get ______ kW solar energy per square meter.
    
    
    
    1. 1.353
    2. 0.66
    3. 47
    4. 3.8 x 10²⁶
    
    
    
    
15. Solar furnace at Mount Louis in France attains the temperature as high as ______ ° C.
    
    
    
    1. 2000
    2. 2500
    3. 3000
    4. 3500
    
    
    
    
16. A solar cell made of thin selenium wafer converts ______ % solar energy into electrical energy.
    
    
    
    1. 0.4
    2. 0.55
    3. 0.7
    4. 1.2
    
    
    
    
17. A thin wafer of ______ converts solar radiation in to electricity.
    
    
    
    1. sodium
    2. strontium
    3. stibium
    4. selenium
    
    
    
    
18. ______ is a semi-metal.
    
    
    
    1. Lead
    2. Carbon
    3. Silicon
    4. Mercury
    
    
    
    
19. ______ is used to make a solar cell.
    
    
    
    1. Silicon
    2. Graphite
    3. Mercury
    4. Platinum
    
    
    
    
20. What is used generally as connecting material in solar panels.
    
    
    
    1. Silicon
    2. Silver
    3. Selenium
    4. Germanium
    
    
    
    
21. Windmill was invented by _______about 250 years ago.
    
    
    
    1. the Chinese
    2. the Indians
    3. the Persians
    4. the Greek
    
    
    
    
22. How much electricity does the largest windfarm at Kanyakumari generate ?
    
    
    
    1. 200 MW
    2. 300 MW
    3. 400 Mw
    4. 500 MW
    
    
    
    
23. The Hydroelectric power-station on river Tapi in Gujarat is ______.
    
    
    
    1. Ukai
    2. Dhuvaran
    3. Panam
    4. Kadana
    
    
    
    
24. A high tide occurs ______.
    
    
    
    1. on every new moon day
    2. on every full moon day
    3. both on new moon and full moon day
    4. any time
    
    
    
    
25. Which of the following is not a product obtained by decomposition of wood ?
    
    
    
    1. Coal tar
    2. Coal gas
    3. Charcoal
    4. Wood pulp
    
    
    
    
26. The calorific value of biogas is ______ kJ/g.
    
    
    
    1. 30 - 35
    2. 35 - 40
    3. 40 - 45
    4. 45 - 50
    
    
    
    
27. Peat coal consists about_______ % carbon.
    
    
    
    1. 27
    2. 30
    3. 80
    4. 96
    
    
    
    
28. ______ is the coal of best quality.
    
    
    
    1. Peat
    2. Lignite
    3. Bitumin
    4. Anthracite
    
    
    
    
29. The Greek word 'petro' means ______.
    
    
    
    1. oil
    2. rock
    3. black liquid
    4. fuel
    
    
    
    
30. Usually petroleum is formed under ______.
    
    
    
    1. igneous rocks
    2. sedimentary rocks
    3. metamorphic rocks
    4. any rock
    
    
    
    
31. _______ (in 1855 AD) proved that petroleum (crude oil) can be used as a substitute of coal.
    
    
    
    1. Professor Brown
    2. Professor Barwood
    3. Professor Byron
    4. Professor Benjamin
    
    
    
    
32. During the refining of petroleum, the fraction having highest boiling temperature ______.
    
    
    
    1. condenses first
    2. condenses last
    3. does not condense
    4. remains in gaseous form
    
    
    
    
33. The calorific value of petrol is ______ kJ/g.
    
    
    
    1. 45
    2. 46
    3. 47
    4. 48
    
    
    
    
34. The number of carbon atoms in hydrocarbon molecule of kerosene is ______.
    
    
    
    1. 5 - 8
    2. 8 - 11
    3. 10 - 14
    4. 12 - 16
    
    
    
    
35. What is the calorific value of kerosene ?
    
    
    
    1. 45 kJ/g
    2. 46 kJ/g
    3. 47 kJ/g
    4. 48 kJ/g
    
    
    
    
36. What is the calorific value of diesel ?
    
    
    
    1. 45 kJ/g
    2. 46 kJ/g
    3. 47 kJ/g
    4. 48 kJ/g
    
    
    
    
37. In Gujarat ______ powerstation uses natural gas to produce electricity.
    
    
    
    1. Ukai
    2. Dhuvaran
    3. Tarapur
    4. Sardar Sarovar
    
    
    
    
38. The calorific value of ethanol is ______ kJ/g.
    
    
    
    1. 25
    2. 30
    3. 33
    4. 35
    
    
    
    
39. The calorific value of a hydrocarbon is higher if its ______.
    
    
    
    1. hydrogen : carbon ratio is higher
    2. hydrogen : carbon ratio is lower
    3. hydrogen : carbon ratio is unity
    4. hydrogen content is zero
    
    
    
    
40. The specific heat of water is _______.
    
    
    
    1. 4.186 kJ/g° C
    2. 4.186 cal/g° C
    3. 4.186 J/g° C
    4. 4.186 J/kg° C
    
    
    
    
41. The formula to find the calorific value of wax is ______.
    
    
    
    1. m x s x t
    2. w x s x t
    3. m x s x t x w
    4. m x s x t /w
    
    
    
    
42. 1 eV = _______ joule.
    
    
    
    1. 1.6 x 10^-17
    2. 1.6 x 10^-18
    3. 1.6 x 10^-19
    4. 1.6 x 10^-20
    
    
    
    
43. According to the theory of relativity
    
    
    
    1. E = m²c
    2. E = mc²
    3. E² = mc
    4. m = E²c
    
    
    
    
44. ______ contribute to the mass of an atom.
    
    
    
    1. Protons only
    2. Neutrons only
    3. Protons and neutrons
    4. Protons and electrons
    
    
    
    
45. If A is the atomic mass, Z is the atomic number and N is the number of neutrons in an atom, then
    
    
    
    1. A = N + Z
    2. N = A + Z
    3. Z = A + N
    4. A + Z + N = 0
    
    
    
    
46. _________invented artificial radioactivity.
    
    
    
    1. Marie Curie
    2. Berkley
    3. Lord Rutherford
    4. Maxwell
    
    
    
    
47. When uranium is bombarded by a neutron it splits into _______.
    
    
    
    1. barium and lanthanum
    2. barium and krypton
    3. lanthanum and boron
    4. boron and krypton
    
    
    
    
48. When uranium is bombarded by a neutron an element emitting _______ is produced.
    
    
    
    1. α-particles
    2. β-particles
    3. γ-rays
    4. x-rays
    
    
    
    
49. According to the Einstein's equation, E = mc², 1 u of mass is converted into _______ MeV of energy.
    
    
    
    1. 901
    2. 911
    3. 921
    4. 931
    
    
    
    
50. The energy produced by the fission of 1 kg of₉₂ U²³⁵ is equivalent to that produced by ______ tons of coal.
    
    
    
    1. 1000
    2. 1500
    3. 2000
    4. 2500
    
    
    
    
51. How many neutrons are released at the end of each splitting of an atom ?
    
    
    
    1. 2 - 3
    2. 3 - 4
    3. 4 - 5
    4. 1 - 2
    
    
    
    
52. What is the required temperature to expedite thermonuclear fusion reaction ?
    
    
    
    1. 10⁶ K
    2. 10⁸ K
    3. 10⁹ K
    4. 10¹⁰ K
    
    
    
    
53. The energy of a neutron released during a fission process should be reduced by about ______ part to convert it into a thermal neutron.
    
    
    
    1. 10²
    2. 10⁵
    3. 10⁸
    4. 10^-5
    
    
    
    
54. Which one of the following is not a naturally occuring isotope of uranium ?
    
    
    
    1. U²³⁸
    2. U²³⁶
    3. U²³⁵
    4. U²³⁴
    
    
    
    
55. In India, about ______ % of total power is generated by using nuclear energy.
    
    
    
    1. 3
    2. 5
    3. 7
    4. 9
    
    
    
    
56. How much energy is produced when two₁H² nuclei fuse to produce ₁H³ and ₁H¹
    
    
    
    1. 1.0 MeV
    2. 3.3 MeV
    3. 4.0 MeV
    4. 1000 MeV
    
    
    
    
57. _______ gm of deuterium is obtained from 1 cubic meter of seawater.
    
    
    
    1. 30
    2. 33
    3. 36
    4. 40
    
    
    
    
58. 1 gallon of deuterrium releases energy equivalent to that released by ______ gallons of petrol after combustion.
    
    
    
    1. 600
    2. 800
    3. 1000
    4. 1200
    
    
    
    
59. Bombardment of neutron on ₃Li⁶ gives _______.
    
    
    
    1. ₀H¹
    2. ₁H¹
    3. ₁H²
    4. ₁H³
    
    
    
    
60. ₁H³ + ₁H² ----> ₂He⁴ + ₀n¹ + _______ MeV.
    
    
    
    1. 16.7
    2. 17.6
    3. 3.3
    4. 4.0
    
    
    
    
61. The radioactive radiations of Chernobyl blast were _______ times the radiation spread during the Hiroshima blast.
    
    
    
    1. 20
    2. 50
    3. 100
    4. 200
    
    
    
    
62. Which of the following is not associated with solar energy ?
    
    
    
    1. Fossil fuel
    2. Hydel energy
    3. Geothermal energy
    4. Wind energy
    
    
    
    
63. How much temperature can be obtained in the solar furnace installed at Mount Louis in France ?
    
    
    
    1. 2000° C
    2. 3000° C
    3. 3500° C
    4. 4000° C
    
    
    
    
64. Which of the following is an optional form of energy ?
    
    
    
    1. Geothermal energy
    2. Natural gas
    3. Petroleum
    4. Hydrogen
    
    
    
    
65. By which process is solar energy converted into chemical energy ?
    
    
    
    1. Evaporation
    2. Greenhouse effect
    3. Photosynthesis
    4. None of the three
    
    
    
    
66. Who was the first scientist to prepare isotopes artificially ?
    
    
    
    1. Fermi
    2. Hann
    3. Rutherford
    4. Strassmann
    
    
    
    
67. 
    
    
    
    
    
    
    

ANSWERS


(1) D (2) C (3) A (4) B (5) C (6) D (7) D (8) B (9) C (10) A (11) C (12) A (13) A (14) B (15) C (16) C (17) D (18) C (19) A (20) B (21) C (22) B (23) A (24) B (25) D (26) B (27) A (28) D (29) B (30) B (31) D (32) A (33) C (34) C (35) D (36) A (37) B (38) B (39) A (40) C (41) D (42) C (43) B (44) C (45) A (46) C (47) B (48) B (49) D (50) D (51) A (52) A (53) C (54) B (55) A (56) C (57) B (58) A (59) D (60) B (61) D (62) B (63) B (64) A (65) C (66) C

SHORT QUESTIONS

ANSWER IN SHORT:

1. What is the primary source of energy ?
   
        ANS :Sun is the primary source of energy.


2. Mention the forms of energy of sun.
   
        ANS :Sun's energy mostly consists of light and heat in the form of solar energy, wind energy, bioenergy, etc.


3. Mention some conventional sources of energy.
   
        ANS :Wood, dung-cakes, coal, kerosene, LPG, petrol, CNG, diesel, electricity, etc. are some conventional sources of energy.


4. What is the full form of energy ?
   
        ANS :The full form of LPG is Liquefied Petroleum Gas.


5. What is the full form of CNG ?
   
        ANS :The full form of CNG is Compressed Natural Gas.


6. Mentiun some nonrenewable sources of energy.
   
        ANS :Petroleum, coal, natural gas, etc. are nonrenewable sources of energy.


7. Why are petroleum, coal, natural gas, etc. called nonrenewable sources of energy ?
   
        ANS :Petroleum, coal, natural gas, etc are called nonrenewable sources of energy because their formation takes millions of years and once utilized they cannot be reformed or regenerated in very short time.


8. Mention direct or indirect sources of Sun's energy. OR Mention the sources of energy having direct or indirect link to the Sun.
   
        ANS :Solar energy, hydel energy, wind energy, tidal energy, biogas, etc. are direct or indirect forms of sun's energy.


9. What do we mean by renewable sources of energy ?
   
        ANS :Those sources of energy which are expected to last for a very long period and which can be regenerated within very short period are called renewable sources of energy.


10. In which form does the radiation from sun reach the earth ?
    
         ANS :The radiation from sun reaches the earth in the form of heat and visible light.


11. What is solar constant ?
    
         ANS :The intensity of solar radiation incident on unit cross-sectional area of earth exposed perpendicularly to the rays of sun at an average distance is called solar constant. Its value is 1.353 kW/m².[NOTE : "average distance" means 'average distance between earth and sun].


12. What is the wavelength of visible light ?
    
         ANS :The wavelength of visible light is 4000 A° to 8000 A° or 4 x 10^-7 m to 8 x 10^-7 m.


13. Give two examples of electromagnetic waves having wavelength less than that of ultraviolet rays.
    
         ANS :X - rays and γ - rays are examples of electromagnetic waves having wavelength less than that of ultraviolet rays.


14. How much of the sunlight passing through the atmosphere consists of infrared rays ?
    
         ANS :About one-third of the sunlight passing through the atmosphere consists of infrared rays.


15. What is the property of infrared rays ?
    
         ANS :Infrared rays are invisible and they can heat the object kept in their path.


16. Mention some devices using solar energy.
    
         ANS :Solar cooker, solar water heater, solar water pump, photoelectric cell, photovoltaic cell, etc are some devices using solar energy.


17. Mention the two categories of devices using solar energy.
    
         ANS :The two categories of devices using solar energy are :(1) devices that convert solar energy into heat and (2) devices that convert solar energy into electricity.


18. How much temperature is developed in solar cooker in 2-3 hour's time ?
    
         ANS :Temperature of about 100 - 140 °C (approx) is developed in solar cooker in 2-3 hour's time.


19. Which country prepared solar cooker industrially for the first time ?
    
         ANS :India (in 1962 AD) prepares solar cooker industrially for the first time.


20. What is the principle of solar concentrators ?
    
         ANS :A solar concentrator works on the following principle : A parallel beam of light incident on a concave mirror is focussed on the principal axis after reflection.


21. What type of reflectors are used generally in solar concentrators ?
    
         ANS :Large spherical or parabolic reflectors are used generally in solar concentrators.


22. What is the temperature achieved in simple domestic solar concentrator (heater) ?
    
         ANS :Approximately 180 - 200 °C temperature is achieved in domestic solar heaters.


23. What is a solar tower ?
    
         ANS :A solar concentrator kept at a height of 50 - 70 m from the ground, consisting of small plane mirrors to generate electricity from solar radiation is called a solar tower.


24. How many small mirrors are there in the solar furnace at Mount Louis in France ?
    
         ANS :There are more than 3500 small mirrors in the solar furnace at Mount Louis in France.


25. What is a solar cell ?
    
         ANS :Solar cell is a device which converts solar energy into electrical energy.


26. Where is the electrical energy produced by solar cells stored conventionally ?
    
         ANS :Convwntionally, the electrical energy produced by solar cells is stored in storage batteries.


27. Which type of energy does wind possess ?
    
         ANS :Wind possesses kinetic energy.


28. What is the basis of deciding the parameters like the height and the number of blades of a windmill ? OR On what basis is the windmill designed ?
    
         ANS :Average wind velocity and local environmental (geographical) parameters are the basis of deciding the parameters like the height and the number of blades of a windmill.


29. Where are the wind energy farms located in Gujarat ?
    
         ANS :Wind energy farms are located at Lamba near Porbandar, at Okha, Mandvi and at Dhank in Gujarat.


30. Where is the largest wind-energy farm located in India ?
    
         ANS :The largest wind-energy farm in India is located near Kanyakumari in Tamilnadu.


31. What is the full form of OTEC ?
    
         ANS :The full form of OTEC is Ocean Thermal Energy Conversion.


32. What is the full form of SRPP ?
    
         ANS :The full form of SRPP is Solar Run Power Plant.


33. For what is the OTEC process used ?
    
         ANS :OTEC process is used to convert thermal energy into electrical energy using temperature difference of oceanic waters flowing at different depths.


34. What is the benefit of ocean thermal energy ?
    
         ANS :The benefit of ocean thermal energy is that this energy is available round the clock whereas solar energy is available only during the daytime.


35. What is a tide ?
    
         ANS :The everyday movement of water level along the sea-shore is called tide.


36. What is tidal energy ?
    
         ANS :Tidal energy is the energy generated by the rise and fall of oceanic tides.


37. Tidal energy is an indirect form of solar energy. True or false ?
    
         ANS :This is a true statement.


38. What is geothermal energy ?
    
         ANS :Geothermal energy is the energy obtained from the heat of hot dry rocks in the earth's crust, geysers, hot springs, etc.


39. What is magma ?
    
         ANS :Magma is hot semifluid formed due to melting of rocks by interior heat of the earth.


40. What are hot spots ?
    
         ANS :'Hot spots' are places below the surface of the earth where hot molten magma settles after being pushed there by geological changes.


41. What is the temperature of hot-water geysers ?
    
         ANS :The temperature of hot-water geysers is about 700 °C.


42. Where are hot-water geysers found in Gujarat ?
    
         ANS :In gujarat, hot-water geysers are found at places like Unai, Tulsi Shyam in Saurashtra and at Lasundra and Tuva village in Godhra district.


43. What contributes to biomass ?
    
         ANS :Dead bodies of living organisms and their excretory products contribute to biomass.


44. Which process is basic in the formation of biomass ?
    
         ANS :Photosynthesis is the basic process in the formation of biomass.


45. Biomass is a direct form of solar energy. True or false ?
    
         ANS :No, this is a false statement.


46. Mention the route through which bioenergy is obtained.
    
         ANS :The route through which bioenergy is obtained is :
    
    Solar energy -> Photosynthesis -> Biomass -> Bioenergy.


47. How much energy of wood is used when burnt in traditional chulhas ?
    
         ANS :About 8 - 10 % of the energy of wood is used when burnt in traditional chulhas.


48. How is charcoal obtained from wood ?
    
         ANS :When wood is burnt with a limited supply of oxygen, it decomposes; volatile impurities and water are vaporised and charcoal is obtained as residue.


49. What does biogas contain ?
    
         ANS :Biogas contains about 65 - 75 % methane, 30 - 40 % carbon dioxide and traces of hydrogen, hydrogen sulphide and nitrogen.


50. Why is biogas traditionally called Gober gas ?
    
         ANS :Biogas is traditionally known as gober gas because it is obtained from the solid waste of animal dung, sewage,crop residue, vegetable wastes, poultry droppings as well as wastes from agro-based industries.


51. Mention two designs of biogas plants used in India.
    
         ANS :The two designs of biogas plants used in India are : (1) Fixed-dome type (2) Floating gas-holder type.


52. What is the full form of KVIC ?
    
         ANS :The full form of KVIC is Khadi and Village Industries Commission.


53. Where are the floating gas-holder type biogas plants used ?
    
         ANS :The floating gas-holder type biogas plants are used where animal dung is used to obtain biogas.


54. Where are the fixed-dome type biogas plants used ?
    
         ANS :The fixed-dome type biogas plants are used where human excreta and other wastes are used to obtain biogas.


55. Write the equation for the combustion of hydrogen.
    
         ANS :H₂ + 1/2 O₂ ---> H₂O + Heat


56. What is the main limitation of hydrogen as a source of energy ?
    
         ANS :The main limitation of hydrogen as a source of energy is that its combustion is explosive in nature.


57. When and where was the first coal mine in India dug /
    
         ANS :The first coal mine in India was dug in Raniganj of West Bengal in 1854 AD.


58. Mention the percentage of carbon in bituminous and anthracite coal.
    
         ANS :Bituminous coal contains about 78 - 87 % carbon and anthracite coal contains about 94 - 98 % carbon.


59. Mention one major use of coke.
    
         ANS :One major use of coke is as a reducing agent in metallurgy.


60. Where and when was the first oil well dug in India ?
    
         ANS :The first oil well in India was dug in 1867 AD in Makkum in Assam (This was the first oil well dug in Asia).


61. Where and when was the world's first oil well dug ?
    
         ANS :The world's first oil well was dug in 1859 AD in Pennsylvania (USA).


62. How much of total crude oil of India is obtained from Gujarat ?
    
         ANS :About 50% of total crude oil of India is obtained from Gujarat.


63. What are the usual height and diameter (width) of a fractional distillation tower ?
    
         ANS :The usual height and diameter of a fractional distillation tower are 31 m and 3 m, respectively.


64. What do petroleum gases mainly consist of ?
    
         ANS :Petroleum gases mainly consist of methane, ethane, propane and butane.


65. What is the full form of LPG ?
    
         ANS :The full form of LPG is Liquefied Petroleum Gas.


66. What is LPG ? OR What does LPG contain ?
    
         ANS :LPG is butane gas in compressed (liquefied) state.


67. What is added to LPG to detect leakage ?
    
         ANS :A foul smelling chemical (mercaptan) is added to LPG to detect leakage.


68. Mention the temperature range during which petrol (gasoline) is obtained.
    
         ANS :Petrol is obtained between the temperatures 40°C to 200 °C.


69. What is the proportion of petrol in petroleum ?
    
         ANS :The proportion of petrol in petroleum is about 45%.


70. During which temperature range is kerosene obtained from petroleum ?
    
         ANS :Kerosene is obtained from petroleum between 200°C to 300°C.


71. Who invented diesel ?
    
         ANS :Rudolf Diesel invented diesel.


72. How many carbon atoms are there in the hydrocarbon molecules of diesel ?
    
         ANS :There are 14 - 20 carbon atoms in the hydrocarbon molecules of diesel.


73. What is the boiling range of diesel ?
    
         ANS :The boiling range of diesel is 300°C to 350°C.


74. What is the boiling range of lubricating oil ?
    
         ANS :The boiling range of lubricating oil is 350°C to 400°C.


75. Mention the uses of lubricating oil.
    
         ANS :Lubricating oil is used for the preparation of wax and grease.


76. What is the main component of natural gas ?
    
         ANS :Methane is the main component of natural gas.


77. What is the full form of CNG ?
    
         ANS :The full form of CNG is Compressed Natural Gas.


78. Define combustion.
    
         ANS :Combustion is the process by which a substance burns and produces heat and/ or light.


79. Define Ignition temperature.
    
         ANS :The minimum temperature at which a substance starts burning in presence of oxygen is called its ignition temperature.


80. Define complete combustion.
    
         ANS :The process of combustion which takes place in sufficient supply of oxygen and releases maximum heat energy is called complete combustion.


81. Define incomplete combustion.
    
         ANS :The process of combustion which takes place in insufficient supply of oxygen and produces light due to yellow flame is called incomplete combustion.


82. Define Calorific value of fuel.
    
         ANS :The heat liberated by complete combustion of 1 gram of fuel is called the calorific value of that fuel.


83. Mention the calorific values of charcoal and wood.
    
         ANS :The calorific value of charcoal is 33 kJ/g and that of wood is 17 kJ/g.


84. Which fuel has the highest calorific value ? How much ?
    
         ANS :Hydrogen has the highest calorific value of 150 kJ/g.


85. What is the calorific value of methane ?
    
         ANS :The calorific value of methane is 55 kJ/g.


86. What is the calorific value of dung-cake ?
    
         ANS :The calorific value of dung-cake is 7 - 8 kJ/g.


87. Define : 1 atomic mass unit.
    
         ANS :One atomic mass is the mass equivalent to 1/12 of the mass of an unexcited C¹² isotope of carbon.


88. What is the rwlation between atomic mass unit (u) and kg ?
    
         ANS :1 u = 1.66 x 10^-27 kg.


89. Which are the units of mass and energy used in Solid-state physics ?
    
         ANS :In solid-state physics the unit of mass is atomic mass unit (u) and the unit of energy is 'electronvolt' (eV).


90. Define : Electronvolt.
    
         ANS :The change in the energy of an electron when it passes through two points having a potential difference of 1 V is called 1 electrovolt(eV) of energy.


91. What is the relation between the units of mass and energy ?
    
         ANS :The relation between the units of mass and energy is:
    
          1 u (mass) = 931.48 MeV (energy)
    
    [Here MeV stands for mega electronvolt]


92. What is meant by nucleons ?
    
         ANS :Nucleons mean protons and neutrons in the nucleus of an atom.


93. In the symbol _ZX^A, what are A and Z if X is an element ?
    
         ANS :A is the atomic mass (weight) and Z is the atomic number of element X.


94. If for an element X we write ₁₁X²³, then what is the number of neutrons in X ?
    
         ANS :The number of neutrons is 12 (23 - 11 =12).


95. Which are the elements called 'transuranic' ?
    
         ANS :Elements having atomic number Z greater than or equal to 92 are called transuranic elements.


96. What is nuclear fission ?
    
         ANS :A nuclear reaction in which a heavy nucleus (uranium for example) splits into two parts (products) which results in the emission of neutrons and energy is called nuclear fission.


97. In which elements does ₅₆Ba¹³⁹ get converted after the emission of β-particles ?
    
         ANS :₅₆Ba¹³⁹ get converted to ₅₇La¹⁴⁰ after the emission of β-particles.


98. When an atom of ₉₂U²³⁵ is bombarded by a neutron, a transuranic element is produced. True or false ?
    
         ANS :This is a false statement.


99. Mention the two categories of nuclear fission.
    
         ANS :Prompt fission and Delayed fission are the two categories of nuclear fission.


100. What is the range of atomic mass of two products obtained after nuclear fission ?
     
          ANS :The atomic mass of the heavy nucleus is in the range of 130 - 149 u and that of the light nucleus is in the range of 85 - 104 u.


101. What is spontaneous fission ?
     
          ANS :The process of fission of some heavy elements and isotopes without being bombarded by any projectile (neutrons) is called spontaneous fission.


102. How many nuclei of ₉₂U²³⁵ should be split by fission to produce 1 Ws (watt second) energy ?
     
          ANS :3.1 x 10¹⁰ nuclei/second should be split by fission to produce 1 Ws energy.


103. How much energy is produced by the fission of 1 kg of ₉₂U²³⁵ ?
     
          ANS :About 1000 MW-day energy is produced by the fission of 1 kg of ₉₂U²³⁵.


104. What is the full form of BARC ?
     
          ANS :The full form of BARC is Bhabha Atomic Research Centre.


105. Mention the locations of nuclear power plants established in India by Nuclear Power Corporation (of India) or NPC.
     
          ANS :NPC has established power plants in (i) Kakrapar in Gujarat (ii) Tarapore in Maharashtra (iii) Kota in Rajasthan (iv) Kalpakkam in Tamilnadu and (v) Narora in U.P.


106. What do we mean by chain reaction ?
     
          ANS :If in a reaction the products of one step result in producing the subsequent step of the reaction then that reaction is called CHAIN REACTION.OR A reaction that is self-sustaining as a result of the products of one step initiating a subsequent step is called CHAIN REACTION.


107. What are thermal neutrons ?
     
          ANS :Thermal neutrons are neutrons which are in thermal equilibrium with the environment at room temperature.


108. How much is the energy of a neutron released during fission ?
     
          ANS :The energy of a neutron released during fission is about 2 MeV.


109. How much is the energy of a thermal neutron ?
     
          ANS :The energy of a thermal neutron is about 0.04 eV.


110. What is a 'moderator' in a nuclear reaction ?
     
          ANS :Moderator is a substance that slows down neutrons released in a nuclear reactor, makinh them more likely to cause fission of ₉₂U²³⁵ and less likely to be absorbed by ₉₂U²³⁸. OR Moderator is a substance that lowers the energy of a neutron released during fission to thermal neutron energy range of 0.04 eV.


111. Mention two substances used as moderator in nuclear reactors.
     
          ANS :Graphite and heavy water are used as moderator in nuclear reactors.


112. Which coolants are used to cool down moderators ?
     
          ANS :Air, water, liquid sodium metal, etc. are used as coolants to cool down moderators.


113. Mention three isotopes of naturally occuring uranium.
     
          ANS :The isotopes of naturally occuring uranium are : ₉₂U²³⁴ ₉₂U²³⁵ and ₉₂U²³⁸.


114. Mention the proportion of different isotopes of uranium.
     
          ANS :The proportion of each isotope of uranium is : ₉₂U²³⁴ - 0.058%, ₉₂U²³⁵ - 0.715% and ₉₂U²³⁸ - 99.28%.


115. What is 'enrichment of uranium'?
     
          ANS :Enrichment of uranium is a specific process by which the proportion of ₉₂U²³⁵ (natural uranium) is increased substantially.


116. What is deuteron ?
     
          ANS :Deuteron is the nucleus of a heavy hydrogen atom which contains one proton and one neutron.


117. What is nuclear fusion ?
     
          ANS :A nuclear reaction in which two atomic nuclei combine to form a heavier nucleus with the release of a large amount of energy is called nuclear fusion.


118. What is 'missing mass'?
     
          ANS :Missing mass is the difference of the sum of the masses of fusing nuclei and the mass of the nucleus formed after fusion.


119. How much energy is produced when two ₁H² nuclei fuse to form ₂He³ and ₀H¹ ?
     
          ANS :When two ₁H² nuclei fuse to form ₂He³ and ₀H¹, 3.3 MeV energy is produced.


120. How is tritium obtained ?
     
          ANS :Tritium is obtained by bombardment of a neutron on an isotope of lithium.


121. What is plasma ?
     
          ANS :A highly ionised gas in which the number of moving negatively charged electrons is equal to the number of positively charged ions is called plasma.


122. What is thermonuclear fusion ?
     
          ANS :The fusion of two or more nuclei into one heavy nucleus due to the temperature being greater than 10⁶ K is called thermonuclear fusion.


123. Which process is used in the weapons of mass destruction like hydrogen bomb ?
     
          ANS :Uncontrolled thermonuclear fusion process is used in the weapons of mass destruction like hydrogen bomb.


124. What is the full form of IPR ?
     
          ANS :The full form of IPR is the Institute of Plasma Research.


125. What is the function of IPR (Institute of Plasma Research) ?
     
          ANS :IPR in Gujarat does research work on obtaining useful energy by Controlled thermonuclear fusion.


126. Mention where and when in Russia did nuclear explosion occur ?
     
          ANS :An explosion in a nuclear reactor occured in Chernobyl of Russia in 1986.(Chernobyl is now in Ukraine).


127. What is meant by nonrenewable source of energy ?
     
          ANS :A source of energy which takes very long time ( in terms of millions of years) for the formation and which cannot be regenerated in very short time is called a nonrenewable source of energy.


128. What are infrared rays ?
     
          ANS :Infrared rays are electromagnetic waves with wavelength more than 8000 A°.


129. 
     
          ANS :

MAGNETIC EFFECTS OF ELECTRIC CURRENT - III : LONG ANSWERS

*INDEX-TOPIC SEARCH

GIVE ANSWER IN DETAIL

1. Explain the presence of magnetic field due to electric current.
   
   ANS:
   
   
   
   
   
   • Danish physicist H.C.Oersted was the first to observe the presence of magnetic field due to electric current during an experiment.
     
   • As shown in figure, a magnetic needle kept near a conducting wire connected in a circuit shows no deflection(figure 1) when there is no current flowing through the conductor.
     
   • When current is allowed to pass through the conductor, the needle shoes deflection(figure 2).
     
   • If the terminals of the battery are reversed(i.e. the direction of the current is reversed), the needle shows deflection in opposite direction.
     
   • These observations clearly show that when current passes through a conductor it behaves as a magnet,i.e. it possesses a magnetic field or a magnetic field is produced when current passes through a conductor.
     
   
   
   
2. EXPLAIN : SOLENOID
   
   ANS:
   
   
   
   
   • A coil of many turns of wire wrapped in the shape of a cylinder (which behaves as a magnet when current passes through it) is called a solenoid.
     
   • As shown in figure 1, if a solenoid has N turns, the magnetic field associated with it is N times stronger than the field due to one loop(turn).
     
   • This strength is due to the fact that the direction of current in each turn is the same and the magnetic field produced in each turn of the solenoid adds up, giving a very strong resultant field inside the solenoid.
     
   • If we compare figure 1 and figure 2, we find that the magnetic field of a solenoid is quite similar to that of a bar magnet.
     
   • Thus, one end of a solenoid behaves as north pole and the other as south pole.
     
   
   
   
3. DESCRIBE AN ACTIVITY TO DEMONSTRATE THE PATTERN OF MAGNETIC FIELD LINES AROUND A CURRENT-CARRYING STRAIGHT CONDUCTOR.
   
   ANS:
   
   
   • Take a cardboard and arrange it in a circuit as shown in figure by inserting a wire through the cardboard.
   • Sprinkle some iron filings on the cardboard and pass current through the wire.
   • Tap the cardboard gently. The iron filings will align themselves in a pattern of concentric circles around the wire.
   • The concentric circles represent the magnetic field lines produced due to the current passing through the wire.
   • The direction of the magnetic field can be obtained by placing a magnetic compass needle at a point on a circle. The north pole of the needle will point in the direction of the field. The arrows on the circles show the direction of the field.
   • If we reverse the direction of the current, the direction of the magnetic field also gets reversed.
   • We can use 'Right Hand Thumb Rule' to know the direction of the magnetic field associated with the current-carrying conductor. The rule states: Imagine that you are holding the current-carrying wire in your right hand such that the thumb is stretched along the direction of the current, then the fingers would wrap around the conductor in the direction of magnetic field.
     
   
   
   
4. DISTINGUISH BETWEEN ALTERNATING CURRENT AND DIRECT CURRENT.
   
   ANS:
   
   
   
5. EXPLAIN : ELECTRIC MOTOR
   
   ANS:
   
   
   When current passes through a conductor placed in a magnetic field, a force acts on the conductor tending to move it out of the field. This effect is the basis of the electric motor.
   
   As shown in the figure, a rectangular coil ABCD is free to rotate about its axis (the line with breaks). It is placed in a magnetic field. The coil is connected to a commutator XY. X and Y are two halves of a split ring. Brush P is in contact with X and brush Q is in contact with Y. When the current flows as shown, the coil will move in clockwise direction according to the Fleming's Left-hand rule. Since the current passing through the parts AD and BC of the coil is parallel to the magnetic field, they do not experience any force. Because the current passing through parts AB and CD of the coil is perpendicular to the magnetic field lines, the magnetic field will push CD down and AB up. When the coil completes half rotation, Y comes in contact with P and X with Q. The direction of current in AB (and CD) changes. This change pushes AB down and CD up. Thus, a continuous rotary motion of the coil is obtained. This is the basic principle of a d.c. motor.
   
   Electric motor is used to convert electrical energy into mechanical energy and thereby to run various machines.
   
   
6. EXPLAIN : ELECTRIC GENERATOR
   
   ANS:
   
   
   If a coil is rotated mechanically in a magnetic field, a current is generated in the coil. This current is called 'induced current' and the process is called 'electromagnetic induction'. Electromagnetic induction is exactly opposite of the motor concept.
   
   As shown in the figure, a rectangular coil ABCD is placed in a magnetic field. The ends of the coil are connected to two halves of a split ring of a commutator XY. The spindle (shown as broken line) supporting the coil is connected to a turbine. When the turbine is rotated mechanically, the coil rotates and a current is generated in it. The current is received at two terminals and supplied as electricity. The galvanometer shows deflection when the coil is rotated indicating the presence of electric current. The current produced in this way is direct current and the generator is called d.c.generator.
   
   
7. EXPLAIN FARADAY'S EXPERIMENT TO EXPLAIN ELECTROMAGNETIC INDUCTION OR EXPLAIN ELECTROMAGNETIC INDUCTION.
   
   ANS:
   • Make a loop of conducting wire and connect it to a galvanometer.
   • Keep a bar magnet near the loop as shown in figure (A). The indicator of the galvanometer shows no deflection indicating that there is no current in the coil.
   • Move the magnet quickly towards the loop as shown in figure (B). The galvanometer shows deflection indicating the presence of current.
   • Pull the magnet quickly away from the loop as shown in figure (C). The indicator shows deflection on the other side indicating that the current is now flowing in the opposite direction.
   • CONCLUSION : (i)When there is a relative motion between the magnet and the loop, voltage and hence current is induced in the conducting loop due to a change in the magnetic field linked with the loop.(ii) The induced current(voltage) in a coil depends on the number of turns in the coil and the rate of change in the magnetic field linked with the coil.
   • The above phenomenon is called electromagnetic induction and the coil is called the inductor.
     
   
   
   
8. EXPLAIN DOMESTIC WIRING WITH DIAGRAM.
   
   ANS :
   
   
   • The figure shows a schematic diagram of a common domestic circuit.
   • The current supplied for domestic use is alternating current(AC) with 50 Hz frequency.
   • A wire with red insulation cover is called 'live wire' or 'phase wire'. Another wire with black insulation cover is called 'neutral wire' or 'negative'.
   • The potential difference maintained between them is 220 V.
   • These wires enter our house through electric meter and fuse board.
   • Two separate lines of 5 A and 15 A are used for different appliances. The 5 A line is used for lamps, T.V., etc. while the 15 A line is used for appliances with higher power ratings like washing machine, geyser, etc.
   • A third wire with green insulation cover is called the 'earth wire' which is connected to a metal plate kept deep in the earth near the house.
   • The earth wire is used as protective measure against the leakage of current, especially from appliances with metallic body such as toaster, electric iron, refrigerator.
   • Parallel connections are used for domestic wiring.
     
   
   
   
9. EXPLAIN : DIRECT CURRENT AND ALTERNATING CURRENT.
   
   ANS:
   • The current flowing from the positive terminal to the negative terminal of a battery is called direct current(dc).
   • The magnitude of the voltage and the current do not change with time and the current flows in one direction only in case of d.c.
   • The graph of current(voltage) v/s time for direct current is a straight line parallel to the time axis.
   • If the current changes its direction between two terminals of the battery periodically then it is called alternating current(ac).
   • The frequency of alternating current is the number of times the current changes its direction in one second. In India, the frequency of a.c. is 50 Hz.
   • The graph of current(voltage) v/s time is a curve in case of a.c.
   • The advantages of using a.c. are :(i)It is easy to produce. (ii)It is relatively cheaper. (iii)The energy loss for long distance transmission is much less.
     
   
   
   
10. EXPLAIN : SAFETY FUSE
    
    ANS:
    
    
    • Safety fuse uses heating effect of electric current.
    • Fuse wire is a wire having low melting point. It is generally made from tin or an alloy of tin and copper.
    • Fuse wire is joined with metallic contacts on an insulation base.
    • If due to some reason, the current in the circuit increases suddenly, the fuse wire melts and breaks the circuit preventing the current going further.
    • Thus, current cannot pass through costly appliances like T.V., freeze, etc., and they are protected from being damaged. Also, probability of an accident or major damage is minimised.
      
    
    
    
11. DISTINGUISH BETWEEN ELECTRIC MOTOR AND ELECTRIC GENERATOR.
    
    ANS:
    

MAGNETIC EFFECTS OF ELECTRIC CURRENT - II : BRIEF ANSWERS

*INDEX-TOPIC SEARCH

ANSWER IN BRIEF

1. Mention the advantages of alternating current(AC).
   

   ANS:The advantages of alternating current(AC) are:
   

   
   
   1. Alternating current is easy to produce.
      
   2. The production of AC is cheaper compared to that of DC.
      
   3. Electricity can be transmitted over longer distances without much loss.
      

   
   

   
   
   
2. Write the Right Hand Thumb Rule and show the diagram explaining it.
   

   ANS:
   
   
   Hold the conducting wire in the right hand such that the thumb is stretched along the direction of the current, then the fingers will wrap around the conductor in the direction of the magnetic field.
   

   
   
   
3. What are the disadvantages of using direct current (DC) ?
   

   ANS:
   The disadvantages of using direct current are:
   

   
   
   1. Its production is comparatively costlier than that of alternating current.
      
   2. The production and distribution of alternating current is easier than that of direct current.
      
   3. The distribution of direct current over long distances involves heavy loss of energy.
      

   
   

   
   
   
4. All domestic appliances are joined in parallel, why ?
   

   ANS:
   All domestic appliances are connected in parallel because :
   

   
   
   • In parallel connection all the appliances are connected between two common points.Therefore all have same voltage equal to that of line voltage across the terminals. Thus all appliances work smoothly with maximum efficiency.
     
   • If an appliance fails or stops due to some reason, the remaining appliances continue to operate because current is still passing through them. Thus, there is no interruption due to breakage of circuit.
     
   • Parallel connection of appliances reduces power loss because the resultant resistance is smaller than individual resistances.
     

   
   

   
   
   
5. Explain the importance of earthing wire (earthwire).
   

   ANS:
   

   
   
   • The earth wire connects the body of an appliance (like an iron or toaster) to the earth via a metal plate kept deep in the earth.
     
   • If due to some fault the live wire comes in contact with the body of the appliance, the earth wire sends the current from the body to the earth and the user gets protection against the possible electric shock.
     
   • Thus, earth wire is needed for the protection of the user.
     

   
   

   
   
   
6. What is the work of a fuse ?
   

   ANS:
   

   
   
   • Fuse is a metal wire having very low melting point and high resistance.
     
   • If due to some reason the current in the circuit increases suddenly, the fuse wire melts and breaks the circuit preventing the current from going further and passing through costly appliances like TV, freeze, etc.
     
   • Thus, costly appliances are protected and the probability of an accident and major damage is minimized.
     

   
   

   
   
   
7. Mention the characteristics of solenoid.
   

   ANS:

   
   
   • Solenoid behaves as a magnet when electric current is passed through the coil.
   • The magnetic field associated with a solenoid is n times stronger than the field due to one loop, if it has n turns in the coil.
   • The magnetic field is similar to that of a bar magnet,i.e., one end of the solenoid behaves as north pole and the other as south pole.
     

   
   

   
   
   
8. 
   

   ANS:
   

   
   

MAGNETIC EFFECTS OF ELECTRIC CURRENT - I :MCQs AND SHORT ANSWERS

MULTIPLE-CHOICE QUESTIONS

*INDEX-TOPIC SEARCH

SELECT THE CORRECT ALTERNATIVE:

1. Who was the first person to notice the magnetic effect of electric current ?
   
   
   
   1. Faraday
   2. Ampere
   3. Oersted
   4. Volta
      
   
   
2. The magnetic field produced due to the current passing through a conductor is proportional to the _______.
   
   
   
   1. electric current
   2. conducting material
   3. length of conductor
   4. diameter of conductor
      
   
   
3. The magnetic field produced at the center of a circular wire is proportional to _______ and inversely proportional to _______.
   
   
   
   1. radius of loop, current
   2. current, radius of loop
   3. length of conductor, current
   4. weight of conductor, current
      
   
   
4. The magnetic field of a solenoid is quite similar to that of
   
   
   
   1. a straight conductor
   2. a horse-shoe magnet
   3. a bar magnet
   4. any magnet
      
   
   
5. The principle of magnetic induction was given by _______.
   
   
   
   1. Michael Faraday
   2. Galileo
   3. Oersted
   4. Ampere
      
   
   
6. The direction of a magnetic field is taken _______.
   
   
   
   1. north to south and back
   2. south to north and back
   3. north to south only
   4. south to north only
      
   
   
7. What is the frequency of the current used domestically in India ?
   
   
   
   1. 50 Hz
   2. 60 Hz
   3. 110 Hz
   4. 220 Hz
      
   
   
8. In our domestic electric supply we use following three colours of wire.
   
   
   
   1. red, blue, green
   2. red, yellow, blue
   3. red, black, green
   4. black, green, yellow
      
   
   
9. The insulation cover on the earth wire is _______.
   
   
   
   1. red
   2. black
   3. green
   4. white
      
   
   
10. The current passing through two separate lines (circuits) of our houses is _______ A and _______ A.
    
    
    
    1. 5, 10
    2. 5, 15
    3. 10, 15
    4. 2, 5
       
    
    
11. The direction of magnetic field lines is taken
    
    
    
    1. north to south
    2. south to north
    3. entering both poles
    4. leaving both poles
       
    
    
12. The magnetic field due to electric current in a conductor is _______.
    
    
    
    1. in the direction of electric current
    2. in the direction opposite to electric current
    3. circular around the conductor
    4. in the center of the conductor
       
    
    
13. Which device is used to convert electric energy into mechanical energy ?
    
    
    
    1. electric generator
    2. solenoid
    3. electric motor
    4. electric iron
       
    
    
14. The principle of electric generator is _______.
    
    
    
    1. conversion of electrical energy into mechanical energy
    2. conversion of electrical energy into thermal energy
    3. conversion of mechanical energy into electrical energy
    4. conversion of electrical energy into light energy
       
    
    
15. Magnetic lines of force inside a solenoid are...
    
    
    
    1. from N to S
    2. from S to N
    3. circular
    4. intersect one another
       
    
    

ANSWERS


(1) C (2) A (3) B (4) C (5) A (6) C (7) A (8) C (9) C (10) B (11) A (12) C (13) C (14) C (15) B

SHORT QUESTIONS

ANSWER IN SHORT:

1. Who provided the first evidence of connection between electricity and magnetism ? When ?
   
        ANS :Danish physicist H.C.Oersted in 1820 AD provided the first evidence of connection between electricity and magnetism.
   
2. Why is a magnetic needle placed near a current carrying conductor deflected ?
   
        ANS : A magnetic needle placed near a current carrying conductor is deflected because the current carrying conductor possesses a magnetic field.
   
3. State the Right-hand Thumb Rule.
   
        ANS : Hold the conducting wire in the right hand such that the thumb is stretched along the direction of the current, then the fingers will wrap around the conductor in the direction of the magnetic field.
   
4. What is a solenoid /
   
        ANS : A coil of many turns of wire wrapped in the shape of a cylinder is called a solenoid.
   
5. What is 'induced electric current'?
   
        ANS : The electric current produced in a loop of conductor due to the relative motion of a magnet within the loop(coil) is called induced electric current.
   
6. What is electromagnetic induction ?
   
        ANS : Electromagnetic induction is the production of electromotive force(voltage) in a conductor when there is relative motion of the conductor within a magnetic field.
   
7. What is an electric motor ?
   
        ANS : An electric motor is a device that converts electrical energy into mechanical energy.
   
8. Write the principle of electric motor.
   
        ANS : An electric motor converts electrical energy into mechanical energy by using the principle that in an electric field the current-carrying conductor experiences force.
   
9. What is an armature ?
   
        ANS : A loop(coil) wound on an axis along with the commutator is known as an armature.
   
10. Name some gadgets where an electric motor is used.
    
         ANS : Fan, mixer, washing machine, fridge, water pump, etc.are examples of gadgets where an electric motor is used.
    
11. What is an electric generator ?
    
         ANS : An electric generator is a device which converts mechanical energy into electrical energy.
    
12. On which principle does an electric generator work ?
    
         ANS : An electric generator works on the principle of electromagnetic induction.
    
13. Mention two types of current.
    
         ANS : The two types of current are :(i) Direct Current, DC (ii) Alternating Current, AC.
    
14. What is direct current ?
    
         ANS : If in a circuit, the current flows from the positive terminal to the negative terminal(i.e. only in one direction) of the battery, the current is called direct current(DC).
    
15. What is alternating current ?
    
         ANS : If in a circuit the voltage and current change their direction between positive and negative terminals periodically with the time, the current is called alternating current(AC).
    
16. Which type of current is supplied/used in domestic lines ?
    
         ANS : Alternating current(AC) is supplied in domestic lines.
    
17. What do we mean by frequency of current ?
    
         ANS : The number of times an alternating current in a circuit changes its direction per second is called the frequency of that current.
    
18. What is the unit of frequency of current ?
    
         ANS : 'Hertz' (Hz) is the unit of frequency of current.
    
19. What is the colour of insulation cover of a 'live wire' or 'phase wire'?
    
         ANS : Red is the colour of insulation cover of a 'live wire' or 'phase wire'.
    
20. Mention the colour of insulation cover of a 'neutral wire' or 'negative wire'.
    
         ANS : The colour of insulation cover of a 'neutral wire' is black.
    
21. To what is the earth wire connected ?
    
         ANS : The earth wire is connected to a metal plate deep in the earth near the house.
    
22. Which is the type of connection used for domestic wiring ?
    
         ANS : The type of connection used for domestic wiring is parallel connection.
    
23. How is an inductor shown in a circuit ?
    
         ANS : ΩΩΩ is the symbol to show an inductor in a circuit.
    
24. What does short-circuit mean ?
    
         ANS : Short-circuit means the positive and negative wires have come into contact with each other due to some fault.
    
25. What is overloading ?
    
         ANS : Overloading is the situation created when many appliances connected in a circuit draw much higher current than the electric line can hold.
    
26. What is a fuse ?
    
         ANS : A fuse is a device consisting of a wire made up of a low melting-point metal/alloy which melts during short-circuit or overloading and prevents accident as well as damage to costly appliances.
    
27. Which metal is generally used to make a fuse wire ?
    
         ANS : Fuse wires are generally made up of pure tin or an alloy of tin with other metals like copper.
    
28. What type of magnetic field arises when current passes through a linear wire ?
    
         ANS : A circular magnetic field( or a field comprising of concentric circles) arises around a linear wire when current passes through it.
    
29. In which part of solenoid do we find uniform magnetic field ?
    
         ANS : We find uniform magnetic field in the central(core) part of a solenoid.
    
30. What is an electromagnet ?
    
         ANS : An iron bar(core) with coils of wire wound around it,which acts as a temporary magnet when an electric current flows through the wire is called ELECTROMAGNET.
    
31. When will the current carrying wire experience maximum force in the magnetic field ?
    
         ANS :When it is placed perpendicularly to the magnetic field.
    
32. The frequency of alternating current is 50 Hz. What does it mean ?
    
         ANS :It means that the current changes its direction alternately 50 times between two terminals in one second.
    
33. 
    
         ANS :
    
34. 
    
         ANS :
    

ELECTRICITY - IV : NUMERICALS

SOLVED NUMERICALS OF TEXT BOOK (GSEB)

*INDEX-TOPIC SEARCH

1. If an electric lamp lights for 2 h drawing 0.4 A of current, calculate the amount of charge that has passed through the lamp.
   
   SOLUTION
   
   Here
   
   Current I = 0.4 A
   
   Time t = 2 h = 2 x 3600 = 7200 seconds
   
   Charge Q = ?
   
   Now, Q = I x t
   
   ∴ Q = 0.4 x 7200 = 2880 = 2.88 x 10³ C        (ANS)



2. How much current will an electric heater having resistance 45 ohm draw if it is connected to a 220 V line ?
   
   SOLUTION
   
   Here
   
   Resistance R = 45 Ω
   
   Voltage V = 220 V
   
   Current I = ?
   
   According to Ohm's law,
   
   I = V/R
   
   ∴ I = 220/45 = 4.89 A        (ANS)
   



3. A lamp of resistance 20 Ω is joined to a battery of 12 V. Find the value of the resistance to be connected in series with the lamp in order to get current of 0.5 A.
   
   SOLUTION
   
   
   
   Here
   
   Voltage V = 12 V
   
   Current I = 0.5 A
   
   Resistance of the lamp R₁ = 20 Ω
   
   Resistance to be connected R₂ = ?
   
   If R is the equivalent resistance of the circuit, then
   
   R = V/I = 12/ 0.5 = 24 Ω
   
   But,       R = R₁ + R₂
   
          ∴ 24 = 20 + R₂
   
          ∴ R₂ = 4 Ω        (ANS)
   



4. Calculate the net(equivalent) resistance of the circuit if resistances of 10 Ω, 5 Ω and 15 Ω are connected in parallel.
   
   SOLUTION
   
   Let the three resistances connected in parallel be
   
   R₁ = 10 Ω, R₂ = 5 Ω, R₃ = 15 Ω
   
   If their net resistance is R, then
   
           1/R = 1/R₁ + 1/R₂ + 1/R₃
   
           ∴ 1/R = (1/10) + (1/5) + (1/15)
   
           ∴ 1/R = (3 + 6 + 2)/30 = 11/30
   
           ∴ R = 30/11 = 2.73 Ω        (ANS)
   



5. Three resistances of 5 Ω, 10 Ω and 30 Ω are connected in parallel with a battery of 12 V. Find out(a)the current passing through each resistance, (b)the total current of the circuit,(c) the equivalent resistance of the circuit.
   
   SOLUTION
   
   
   
   Here the three resistances are
   
   R₁ = 5 Ω, R₂ = 10 Ω, R₃ = 30 Ω
   
   Voltage V = 12 V
   
   Let the currents passing through the three resistances be I₁,I₂,I₃,respectively and the equivalent resistance be R.
   
   Using Ohm's law, we get
   
      I₁ = V/R₁
   
       ∴ I₁ = 12/5 = 2.4 A
   
      I₂ = V/R₂
   
       ∴ I₂ = 12/10 = 1.2 A
   
      I₃ = V/R₃
   
       ∴ I₃ = 12/30 = 0.4 A
   
   Thus, net current I = I₁ + I₂ + I₃
   
         ∴ I = 2.4 + 1.2 + 0.4 = 4.0 A
   
   Again, 1/R = 1/R₁ + 1/R₂ + 1/R₃
   
           ∴ 1/R = 1/5 + 1/10 + 1/30
   
           ∴ 1/R = 1/3
   
           ∴ R = 3 Ω       (ANS)



6. In the following figure if five resistors have been connected as shown,find the equivalent resistance and the net current of the circuit.Given R₁ = 10 Ω,R₂ = 40 Ω,R₃ = 30 Ω,R₄ = 20 Ω,R₅ = 60 Ω and voltage of the battery V = 12 V.
   
   
   
   SOLUTION
   
   Here voltage V = 12 V
   
   If the equivalent resistance of R₁ and R₂ is R' then
   
   1/R' = 1/R₁ + 1/R₂
   
   ∴ 1/R' = 1/10 + 1/40 = 0.1 + 0.025 = 0.125
   
   ∴ R' = 1/0.125 = 8 Ω
   
   If R" is the equivalent resistance of R₃, R₄ and R₅ then
   
   1/R" = 1/R₃ + 1/R₄ + 1/R₅
   
   ∴ 1/R" = 1/30 + 1/20 + 1/60 = 1/10
   
   ∴ R" = 10 Ω
   
   If R is the equivalent resistance of R' and R" then
   
   R = R' + R"        (R' and R" are in series)
   
   ∴ R = 8 + 10 = 18 Ω
   
   and current I = V/R = 12/18 = 0.67 A       (ANS)
   



7. If an electric lamp draws 500 mA with voltage of 2.5 V, calculate the power and the energy consumed in 1 minute.
   
   SOLUTION
   
   Here, voltage V = 2.5 V, current I = 500 mA = 0.5 A, time t = 1 min = 60 seconds
   
   Now, power P = V x I = 2.5 x 0.5 = 1.25 watt
   
   and energy consumed in 1 minute W = P x t
   
           ∴ W = 1.25 x 60 = 75 joule       (ANS)
   



8. A 100 W lamp glows for 2 hours per day calculate the energy consumed in 30 days.
   
   SOLUTION
   
   Here power of lamp P = 100 watt = 0.1 kW
   
   time t = 2 x 30 = 60 h       (2 h/day x 30 days)
   
   Now energy consumed in 30 days
   
   W = P x t = 0.1 x 60 = 6 kWh       (ANS)



9. 
   
   SOLUTION

UNSOLVED NUMERICALS OF TEXT BOOK (GSEB)

1. If 300 mA current passes through a lamp, how many electrons will pass through it in 1 minute ?
   
   SOLUTION:
   
   Here, current I = 300 mA = 0.3 A
   
      time t = 1 minute = 60 seconds
   
   Now, charge Q = I x t = 0.3 x 60 = 18 coulomb
   
   and no. of electrons = (total charge)/(charge on 1 electron)
   
       ∴ no. of electrons = (18)/(1.6 x 10^-19)
   
                       = 1.125 x 10²⁰ electrons        (ANS)
   


2. If a current of 5 mA passes through a resistance of 2200 Ω, find out the voltage drop on it.
   
   SOLUTION:
   
   Here, current I = 5 mA = 0.005 A and resistance R = 2200 Ω
   
   Now, voltage drop V = IR = 0.005 x 2200 = 11 V     (ANS)
   


3. Three resistors R₁ = 5 Ω, R₂ = 8 Ω and R₃ = 12 Ω are connected in series with a battery of 4 V. Find the value of current in the circuit and the voltage drop across each resistor.
   
   SOLUTION:
   
   
   Here,
   
   Equivalent resistance R = R₁ + R₂ + R₃
   
          ∴ R = 5 + 8 + 12 = 25 Ω
   
   Now, current I = V/R =4/25 = 0.16 A
   
   If V₁, V₂ and V₃ are voltage drops across R₁, R₂, and R₃,respectively, then
   
   V₁ = I x R₁ = 0.16 x 5 = 0.8 V
   
   V₂ = I x R₂ = 0.16 x 8 = 1.28 V
   
   V₃ = I x R₃ = 0.16 x 12 = 1.92 V        (ANS)
   


4. This numerical has been included in the previous one.
   
   SOLUTION:
   Requires no solution.
   


5. Three resistors are joined in parallel. A current of 7.5 A flows due to 30 V battery. If two resistors have resistances of 10 Ω and 12 Ω. Find out the third. Also find the current passing through each resistor.
   
   SOLUTION:
   
   
   
   Let the three resistances in parallel be : R₁ = 10 Ω, R₂ = 12 Ω and R₃.
   
   Here voltage V = 30 V and current I = 7.5 A
   
   ∴ Net resistance of the circuit R = V/I = 30/7.5 = 4 Ω
   
   Also, 1/R₁ + 1/R₂ + 1/R₃ = 1/R
   
   ∴ 1/10 + 1/12 + 1/R₃ = 1/4
   
   ∴ 1/R₃ = 1/4 - 1/10 - 1/12 = 1/15
   
   ∴ R₃ = 15 Ω
   
   If I₁, I₂ and I₃ are the currents passing through R₁, R₂ and R₃ respectively, then
   
   I₁ = V/R₁ = 30/10 = 3.0 A
   
   I₂ = V/R₂ = 30/12 = 2.5 A
   
   I₃ = V/R₃ = 30/15 = 2.0 A ___________[ANS]
   


6. Calculate the current flowing through the circuit shown below.
   
   
   
   SOLUTION:
   
   We can draw the circuit as shown below:
   
   
   
   Here R₁ and R₂ are connected in series , therefore, their equivalent resistance R' is given by
   
   R' = R₁ + R₂ = 30 + 30 = 60 Ω
   
   Again, R' and R₃ are in parallel,so their equivalent resistance R can be calculated by
   
   1/R = 1/R' + 1/R₃
   
   ∴ 1/R = 1/60 + 1/30 = 3/60 =1/20
   
   ∴ R = 20 Ω
   
   Thus the equivalent resistance of the circuit R = 20 Ω.
   
   Now, current I = V/R =2/20
   
           ∴ I = 0.1 A _________(ANS)
   


7. Two lamps of 100 W and 60 W are joined in parallel with a line voltage of 220 V. Calculate the current flowing through the circuit.
   
   SOLUTION:
   Here, the total power of the lamps P = 100 + 60 = 160 W
   
   Now, current I = P/V = 160/220 = 0.73 A ________(ANS)
   


8. An electric iron draws a current of 5.0 A. If its resistance is 44 Ω, calculate the energy consumed in 5 minutes.
   
   SOLUTION:
   
   Here, current I = 5 A, resistance r = 44 Ω,
   
   time t = 5 minutes = 5 x 60 = 300 seconds.
   
   Now, W = I² R t = (5)²(44)(300) = 330000 J_____(ANS)
   


9. Two lamps of 100 W and 500 W are joined in parallel with a main line. Which lamp will glow brighter ? Why ?
   
   SOLUTION:
   
   The lamp with 500 W will glow brighter because it is using five times the energy used by the 100 W lamp per second.(ANS)
   


10. In a house three lamps of 100 W, 60 W and 40 W are kept on for 25 hours. How many units of energy will be consumed ?
    
    SOLUTION:
    
    The total power of three lamps = 100 + 60 + 40 = 200 W
    
    ∴ Energy consumed in 25 hours = 200 x 25 = 5000 Wh
    
                    = 5 kWh = 5 unit______(ANS)
    


11. 
    
    SOLUTION: