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: