Energy Sources
Q1. Rewire the statement by selecting the correct option.
1. Energy obtained from ________________ is pollution free.
a. Petrol b. coal c. nuclear reactor d. solar cell.
2. The spots are sources of ________________ energy.
a. wind b. geothermal c. nuclear d. hydroelectric.
3. In sun ___________ hydrogen atoms combined together to form a helium nucleus.
a. 2 b. 3 c. 4 d. more than 4
4. Solar ______________ converts solar energy into electricity.
a. cooker b. dryer c. heater d. cell
5. Calorific value of _______________ is height amongst fuels.
a. hydrogen b. methane c. LPG d. biogas.
Q2. Fill in the blanks with proper term fro the bracket at the end of the statement.
1. Renewable energy source is __________________
(Firewood, cowdung, biomass)
2. A device which converts water energy into electrical energy is known as __________
(Solar cell, armature, solar drier)
3. Large inexhaustive source of energy is _______________________
(coal, wood, sun)
4. To remove moisture from the grapes, we use __________________
(solar dryer, solar cooker, solar cell)
5. LPG consists of _______________________
(butane and isobutene, methane and butane, methane and ethane)
Q3. State whether the following statement are true or false.
If the statement is false correct the statement by changing the under lined phrase.
1. Children use solar energy to fly kites.
2. Wind mill converts wind energy into electrical energy.
3. The biogas plant consists of a digester and a cover.
4. The efficiency of chulha is less than 150.
5. The inner surface of solar cooker box is red.
Q4. Give scientific reasons.
Textual Questions
1. Use of fossil fuels created energy crisis.
Answer.
1. Fossil fuels like coal, petroleum and natural gasses have been formed millions of years ago under special circumstance.
2. Since these conditions are not prevailing now, hence these fossils and fuels are rare.
3. These energy sources are extensively used to meet our ever growing demands.
4. If we continue to use these non-renewable energy sources at present rate, their known reserve would deplete at very fast.
5. Hence, use of fossil fuels creates energy crisis.
2. Mini hydroelectric poser stations are preferred.
Answer.
1. Hydroelectric power plants can be constructed only at a limited number of places. Whenever a dam is constructed, large land area gets submerged which causes long term problem of rehabilitation.
2. Besides being free from the problem of pollution, mini – hydroelectric power plants are also free from issues and controversies that are associated with bigger dams.
3. Mini – hydroelectric power stations can be constructed on rivers in the hilly regions.
4. Hence, mini hydroelectric power stations are preferred.
3. Wind mill requires a specific locations.
Answer.
1. Wind energy is used to generate electricity by using wind mill. Electricity generated by a single wind mill is quite small.
2. To generate electricity on a commercial scale a large number of wind mills are erected over a large area. This area is called as wind energy farm.
3. Hence, wind mill requires a specific locations.
4. Farmers winnow the grains.
Answer.
- Wheat harvest contains husk.
- Winnowing helps in separation of the husk from the grains by using wind energy.
- Hence, farmers winnow the grains.
5. We have to search for new renewable energy sources.
Answer.
- Due to excessive industrialisation energy sources such as oil, coal and natural gas are undergoing fast depletion.
- The growth in pollution, increase in energy demand and limited nature of conventional energy resources has resulted in the energy crisis.
- Renewable energy resources are practically inexhaustible, non – polluting and are available in distributed manner
- To overcome these energy crises we have to search for new renewable energy resources.
Non – Textual Questions
1. Wind is a renewable source of energy.
Answer.
- Renewable energy sources have a inherent capacity to regenerate and replenish themselves.
- Wind is the effect of atmospheric pressure difference due to alternate heating and cooling of the earth.
- Hence, wind is a renewable source of energy.
2. Sun is the large inexhaustive source of energy.
Answer.
- Solar energy is continuously produced in the interior of the sun due to the nuclear fusion of hydrogen nuclei at a very high temperature (2 x 107)0C.
- This energy which is produced is radiated in all direction and is received by the earth.
- The power received by the earth is 1.8 x 1011 mW which is many times more than the present consumption rate and future energy needs of the earth.
- Hence solar energy is a large inexhaustive source of energy.
3. It is necessary to store solar energy.
Answer.
1) Solar energy is not a concentrated source of energy.
2) Solar energy availability varies widely with time. The variation the availability of solar energy occurs daily because of day and night cycles.
3) Due to earth’s revolution round the sun, seasonal variations are introduced in the available amount of solar energy.
4) Variations are also caused by local weather conditions such as cloud cover, winds etc.
5) Hence, it becomes necessary to store energy when sun is shinning. This solar energy can be used during the period when solar energy is not directly available.
4. The inner surface of solar cooker box is painted black.
Answer.
1) The black surface absorbs 98% of the incident heat radiation. Solar energy from the glass cover is concentrated inside the box.
2) Inner surface of the cooker absorbs heat and it becomes hot due to which base of the cooking pot and sides get heated. Thus, food gets cooked.
3) Thus, the inner surface of solar cooker box is painted black.
5. Modern solar cells are made up of silicon.
Answer.
1) Silicon is easily available in abundance.
2) It is environmental friendly. Also silicon converts most of the incident solar energy into electrical energy.
3) Hence modern solar cells are made up of silicon.
6. Biomass is a renewable source of energy.
Answer.
1) The resources that have inherent capacity to reappear or replenish themselves by quick cycling, reproduction and replacement within a reasonable time are renewable energy sources.
2) Biomass is a material contained in the bodies of plants and animals.
3) Plants and animals being living beings can be reproduced again and again.
4) Hence, biomass is a renewable source of energy.
7. Biogas is used as a convenient fuel for domestic use.
Answer.
1) Methane is a major constituent of biogas (80%) which is an excellent fuel.
2) So biogas burns without smoke and produces a large quantity of heat.
3) Hence biogas is used as a convenient fuel for domestic use.
8. The storage tank in a solar water heater is kept at higher level.
Answer.
1) Water in the collector is heated by solar energy. It expands and becomes lighter, it flows to the top of the water tank.
2) Hot water is lighter and it remains in the upper part of the tank.
3) Its place is taken by the colder water from the bottom of the tank. Hot water from the top of the tank is available for use.
4) Hence, the storage tank in a solar water heater is kept at higher level.
9. The sludge obtained from the biogas plant is used as an excellent fertilizer.
Answer.
1) The sludge obtained from biogas plant is rich in nitrogenous, phosphatic and potassium compounds.
2) These compounds are important nutrients for plants.
3) Thus the sludge obtained from a biogas plant is used as an excellent fertilizer.
10. Biodiesel is considered as a clear fuel.
Answer.
1) Biodiesel has almost no sulphur, no aromatics.
2) It has 10% built in oxygen which helps it to burn fully.
3) Thus, Biodiesel is considered as a clean fuel.
11. Jatropha plantation has enormous employment generation potential in rural area.
Answer.
1) If waste land in India
2) It is estimated that equivalent amount of Biodiesel will be produced which will fulfil one tenth requirement of diesel in our country.
3) Thus, Jatropha plantation has enormous employment generation potential in rural area.
12. Coal is used as fuel as the source of heat energy in industries for generating electricity.
Answer.
1) The main constituent of coal is carbon.
2) When coal burns, the carbon present in it reacts with oxygen to produce CO2. During this process lot of heat energy is produced.
3) Therefore, coal is used as fuels as the source of heat energy in industries for generating electricity.
13. Coke produces more heat than coal.
Answer.
- The calorific value of a fuel is proportional to is carbon content.
- Coke contains about 90 – 95% carbon while coal contains 27 -98% carbon (depending upon its type)
- Thus, coke produces more heat on combustion than coal.
14. Coke is superior fuel than coal.
Answer.
- The calorific value of a fuel is proportional to is carbon content.
- Coke contains about 90 – 95% carbon while coal contains 27 -98% carbon (depending upon its type)
- Coke burns without producing smoke whereas coal burns with smoke causing pollution.
- Hence, coke is superior fuel than coal.
15. The calorific value of ethane is lower than methane.
Answer.
1. In methane (CH4) a carbon atom is bounded by four hydrogen atoms which upon combining with oxygen produce a large amount of energy.
2. In ethane (C2H4), each carbon atom is bounded with three hydrogen atom.
3. Hence, the calorific value of ethane is lower than methane.
Q5. Distinguish between.
1. Renewable energy sources and Non – Renewable energy sources.
| Renewable energy sources | Non – Renewable energy sources |
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2. Fossil fuel energy and solar energy.
| Fossil Fuel Energy | Solar Energy |
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3. Biomass - biogas
| Biomass | Biogas |
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4. Solar cell – Solar dryer
| Solar cell | Solar dryer |
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Q6. Answer the following questions.
1. Why do we need energy? Explain with examples?
Answer. We need energy in every walk of life, example
- In house, energy is required to cook our food and to light our house, to operate radio and television.
- In industry, we need energy to run various machines,.
- In agriculture – we need energy for irrigation, tractors etc.
2. What are non – renewable energy resources? Give examples
Answer.
- Non – renewable energy resources are those which once used are lost forever and cannot be replenished.
- E.g. Fossil fuels like coal, petroleum and natural gas were formed millions of years ago due to burial of remains of plants and animals.
3. What are renewable energy resources? Give examples.
Answer.
- The resources that have inherent capacity to reappear or replenish themselves by quick cycling, reproduction and replacement within a reasonable time are called as renewable energy resources.
- Example : - wind energy, tidal energy, energy from flowing water, energy from sun, energy from biomass.
4. What are the applications of wind energy?
Answer.
- The wind energy is used by farmers for winnowing to remove husk from grass.
- Wind energy is used in sail boats and wind mills. Wind mills converts wind energy into electrical energy.
- Children use wind energy to play a whirling and to fly kits.
5. What is wind energy farm?
Answer.
- Wind mills converts wind energy into electrical energy.
- Electricity generated by a single wind mill is quite small.
- Therefore, numbers of wind mills are erected over a large area.
- This area is called wind energy farm.
- The energy generated by each windmill is coupled to generate electricity on a commercial scale.
6. Explain the working of wind mill.
Answer.
- Wind mills convert wind energy into electrical energy.
- Wind mill has a structure similar to a large electric fan, that is erected at some height on a rigid support.
- The number of blades, shape of blades and height of the wind mill from ground are decided on the basis of wind velocity
- The blades are designed in such a way that it creates a pressure difference. The pressure difference makes the blades to rotate.
- This rotatory motion of the wind mill is used to rotate the armature of electric generator which generates electricity.
7. How is geothermal energy produced?
Answer.
- The places where magma collected below the surface of the earth are called spot.
- The spots are sources of geothermal energy.
- When underground water comes in contact with spots, water gets converted into steam.
- The steam thus generated is trapped in rocks and gets compressed under high pressure.
- This steam is extracted by sinking pipes through holes drilled upto spot.
- The steam extracted in this way can be utilized to turn turbine of electric generator.
8. Explain the production of solar energy OR
Explain nuclear fusion in the interior of sun.
Answer.
- The interior of the sun mainly contains hydrogen nuclei.
- The temperature of this interior is about (2 x 107)0C. At this extremely high temperature the hydrogen nuclei undergoes nuclear fusion.
- In this process four hydrogen nuclei combine to form one helium nucleus.
- The mass of helium nucleus is slightly less than the total mass of hydrogen nuclei.
- This mass difference is converted into energy.
- As large number of helium nuclei are formed per second and extremely large quantity of energy is continuously liberated by the sun in the form of heat and light.
- This energy is in the form of electromagnetic radiation and is called solar energy.
9. What are the main advantages of solar energy?
Answer.
- Solar energy is an extremely large and inexhaustible source of energy.
- It is a clean source of energy and the use does not effect the environment, while other sources of energy like fossil fuels and nuclear power leads to pollution and other environmental hazards.
10. What are the disadvantages of solar energy?
Answer. The disadvantages of solar energy are
- Solar energy is a dilute source of energy. Even in the hottest regions on the earth, the solar radiations incident per second on one square metre of earth’s surface is less than 1000 joules.
- These values are low from point of technological utilization. In order to collect sufficient amount of energy, large surface areas are required, which are expensive. This increases cost of solar devices.
- Solar energy availability varies widely with time. The variation in the availability occurs daily because of day and night cycle.
- Variation in the available solar energy is also caused by local weather conditions such as cloud cover, wind etc.
- Hence, it becomes necessary to store solar energy when sun is shinning. The storage equipments increase the cost of the system to be used.
11. What are the main components of solar water heater?
Answer. The two main components of solar water heater are flat plate collector and insulated storage tank.
1. What is solar panel?
Answer. A large number of solar cells combined together to produce enough electricity is called a solar panel.
2. Name some solar energy devices and write its uses? OR
What are the applications of solar energy?
Answer. The various applications of solar energy are listed as follows.
- Solar cooker: - It is used to cook food that requires slow cooking. E.g. rice, dal etc.
- Solar water heater: - It is used for heating water.
- Solar cells: - They are used in artificial satellites. They are also used as a source of energy for radio and wireless transmission at TV relay stations.
- Solar dryer: - It is used to remove moisture from the grapes.
3. Name the isotopes of uranium
Answer. The natural uranium has three isotopes 234U, 235U and 238U.
4. What is burner reactor?
Answer. Uranium – 235 undergoes spontaneous fission when bombarded by slow neutrons. These neutrons which are formed as a result of this fission are slowed down by a moderator and made to bombard new nucleus of 235U, there by setting of a controlled chain reaction. The working of the reactor in which this reaction takes place is called burner reactor.
5. What is breeder reactor?
Answer.
- The reactions in which the fertile material gets converted into fissible material are known as breeder reactions.
- 238U is a fertile material and can be converted into fissible material plutonium (239Pu) by neutron bombardment.
- The reactor in which such breeder reactions take place is known as breeder reactor.
6. What is biomass? Write two disadvantages in direct use of biomass resources as fuels.
Answer. The material contained in the bodies of plants and animals is called as biomass. The disadvantages in the direct use of biomass resources as fuels are as follows: -
1. If the biomass wood is burnt in a traditional manner in chulhas, it does not burn completely. This result in the wastage of precious fuel.
2. Incomplete combustion of wood creates pollution which is hazardous to health.
3. Animal cowdung is rich in nitrogenous and phosphatic compounds which can also serve as best fertilizers. Combustion of dung cakes causes a loss of vital nutrients of the soil and also lead to pollution.
7. Explain the indirect use of biomass.
Answer.
- Biomass can be used indirectly by converting it into convenient fuel in solid, liquid and gaseous form.
- There are two conversion processes. These are biological conversion and thermochemical conversion.
- Biological conversion includes processes like fermentation.
- Foe thermochemical conversion, a gasifier is needed, of which end product is a mixture of producer gases like N2, CO, H2, CO2 and CH4.
8. What is biogas? State its components.
Answer.
- Biogas is a fuel produced by microbial decomposition of organic matter in absence of oxygen.
- Biogas is a mixture of methane, carbon dioxide (CO2), Hydrogen (H2) and hydrogen sulphide (H2S).
9. State any two uses of biogas.
Answer.
- Biogas is used to produce mechanical power in agricultural machinery, water – pumping and to generate electricity.
- Biogas is a clean combustion fuel that can be used for cooking, space and water heating and lighting also.
- Thus it is used as fuel in industries and at home.
10. What is bio fuel? What does it include?
Answer.
- Biofuels are renewable energy resources obtained from biomass.
- Biofuels includes ethanol, Biodiesel, biohydrogen and biogas.
11. What are fuels? How are they classified?
Answer. Fuels are the substances, which on combustion produce energy in the form of heat that can be used for various purposes. There are three main types of fuels such as solid fuels, liquid fuels and gaseous fuels.
- Solid fuels:- The main solid fuels are wood, coal and coke.
- Liquid fuels: - The main liquid fuels are petroleum and petro – products namely gasoline. Kerosene, diesel, fuel – oil etc.
- Gaseous fuels: - Gaseous fuels are classified into two main types (i) Natural gases (ii) Artificial gases.
i. Natural gaseous fuels include in methane, ethane, butane etc.
ii. Artificial gaseous fuels include coal gas, oil gas, petrol gas, water gas and producer gas.
12. How are gaseous fuels classified? Give examples.
Answer.
- Gaseous fuels are classified as natural gaseous fuels and artificial gaseous fuels.
- Artificial gaseous fuel includes coal gas, oil gas, petrol gas, water gas and producer gas.
- Natural gaseous fuels include Methane, ethane, butane etc.
13. What is calorific value? State the calorific value of coal, LPG, Kerosene and wood.
Answer. The heat liberated in joule on complete burning of one unit of duel is expressed as it’s calorific value.
| Name of Fuel | Calorific Value KT/g |
| Coal | 25-33 |
| LPG | 55 |
| Kerosene | 48 |
| Wood | 17 |
Q7. Write short notes on
1. Tidal energy
Answer.
- Everyday movement of water level along the shore is known as tides. Tides are generated by the gravitational attraction between the earth and the moon. Tides raise the water level by few meters. The energy possessed by rising and falling water in tides are known as tidal energy.
- Tidal energy is used to produce electricity.
- To generate electricity from a tidal energy, a dam is constructed across narrow opening to the sea.
- The water moves in and out from these openings during tides.
- This water flows over the turbines fixed in the dam. The turbine rotates and generates electricity.
Limitations: -
- Rise and fall of water during tide is insufficient to generate electricity on large scale.
- There are few sites which are suitable to build dams along the coast line.
2. Geothermal energy.
Answer.
- The heat from the interior part of the earth can be used as a source of energy under certain conditions and this energy is called as geothermal energy.
- Rocks melt due to heat from the interior part of the earth. These molten rocks are known as magma.
- Whenever there are some geological changes in some region, the magma is pushed upwards which gets collected at some depth below the surface of the earth.
- These places are called as spots which are the sources of geothermal energy.
- When underground water comes in contact with spots, water gets converted into steam. This steam is extracted by sinking pipes through the holes drilled upto spot.
- This extracted steam can be utilised to turn the turbines of electric generator.
- Geothermal energy can be obtained from natural Geysers also.
3. Solar cells/ Photo voltaic cells
Answer. The devices which convert solar energy directly into electrical energy are known as solar cells (or photo voltaic cells)
- Solar cell consists of number of thin layers of silicon. Silicon is available in abundance and is environmental friendly.
- Silicon converts most of the incident solar energy into electrical energy.
- A typical solar cell is a 2 cm square piece of pure silicon which produces about 0.7 watt electricity when exposed to sunlight.
- Hence, large number of solar cells is combined together. An assembly of such solar cells used to produce electricity is called a solar panel.
Uses: -
- Solar cells are used as source of energy for radio or wireless transmission at TV relay stations, traffic lights and stations in the remote areas.
- They are widely used in calculator and toys.
- They are also used to pump water for irrigation, for lighting in the rural area and remote villages.
4. Biodiesel
Answer. Biodiesel is a renewable energy source. It is extracted from seeds of soyabin and corn.
- Biodiesel is a renewable source of energy. It is produced from Jatropha plants.
- Biodiesel is considered as clean fuel as it has almost o sulphur, no aromatics and has 10% built in oxygen which helps it to burn completely.
- If waste land in
Advantages: -
- It is used as a substitute fuel in place of diesel in diesel engine.
- It is a non – poisonous and it is biodegradable.
5. Breeder Reactions.
Answer.
- The reactions in which fertile material is converted into fissible material are known as breeder reactions. The reactor in which such reactions takes place is known as ‘breeder reactor’.
- E.g. Uranium – 238 is not a fissible material but it is a fertile material. It can be converted into fissible material plutonium (239Pu) by neutron bombardment.
- The neutrons generated in this reaction serve two purposes. First they convert fertile material into fissible material and secondly they sustain fission reaction.
6. Nuclear fusion
Answer.
- In nuclear fusion energy is released by joining very light atoms. Now a days fusion reactions are controlled and fusion reactors are built. These are also ultimate source of energy.
- Deuteron occurs naturally in the sea water and it is estimated that fusion of all deuteron in just one cubic meter of sea water would yield 12 x 109 kj (Kilo – joules)
- Fusion of deuteron is also another ultimate source of energy.
7. Petroleum.
Answer.
- Petroleum is a complex mixture of hydrocarbons.
- Petroleum is extracted from reservoir well in form of a thick – black liquid which is called as crude oil.
- Crude oil cannot be used in a natural form as fuel. Therefore it is refined by fractional distillations.
- After refining petroleum we get various fuels like petrol, diesel, kerosene, paraffin wax and lubricant oil. Petrol, diesel, kerosene heat after combustion leaving no residue.
8. Natural gas.
Answer.
- Natural gas is found in petroleum reservoir well.
- It mainly contains methane.
- It burns easily to produce heat and is supplied through pipes for various domestic as well as industrial purposes.
- Natural gas is subjected to high pressure to obtain compressed natural gas (CNG) which is in a liquid form and can be transported at a long distance through tankers.
9. L.P.G. (Liquidified Petroleum Gas)
Answer.
- L.P.G mainly consists of Liquidified butane and isobutane (C4H10) and is used as a common fuel.
- It is obtained from petroleum.
- It is filled under pressure in metal cylinders and supplied for cooking and industrial use.
10. Solid fuels.
Answer. Wood, coal and coke are solid fuels.
- Wood: - Wood is a common fuel, having cellulose (C6H10O5) as then chief constituent. It burns in the presence of oxygen producing CO2, water vapour and heat energy.
- Coal: - (i) Coal occurs in many forms containing amorphous carbon and carbon compounds.
(ii) The main varieties of coal with increasing percentage of carbon are peat, lignite, bituminous and anthracite.
(iii) When coal is burnt in absence of air the residue left behind is coke.
- Coke: - (i) Coke is obtained when coal is heated in absence of air.
(ii) Coke contains 90 – 95 % carbon and burns without producing smile.
Therefore it produces more heat than coal.
11. Coal.
Answer.
- Coal deposits are formed on the surface of earth as well as below the surface of earth. Main constituent of coal is carbon.
- When coal burns, the carbon present in it reacts with oxygen to produce CO2.
- During this process lot of heat energy is produced.
- Therefore, coal is used as fuel as the source of heat energy in industries for generating electricity.
- Coal is also used as domestic fuel.
12. Gaseous fuels.
Answer. Gaseous fuels are classified into two main types.
i. Natural gases: - It includes methane, butane etc.
ii. Artificial gases: - It includes Coal gas, Oil gas, Petrol gas, Producer gas etc.
a. Coal gas: - It is obtained by fractional distillation of coke.
b. Oil gas: - It is obtained by cracking of kerosene.
c. Petrol gas: - It is obtained by cracking of petrol.
d. Producer gas:- Producer gas is a mixture of carbon monoxide (30%), nitrogen (60%) and other gases (10%). It is mainly used in the glass furnace and in the preparation of ammonia in ammonia plants.
Q8. Answer Briefly.
1. How energy can be obtained from flowing water? Discuss the problems associated with it.
Answer.
- Energy of flowing water is utilized to produce electricity at hydroelectric power station. Dams are constructed to store the water by obstructing flow of water of a river.
- In this process, kinetic energy is converted into potential energy. The water from the top of the dam is allowed to fall through pipes over the turbine blades at the bottom of dam.
- When water falls on the turbine, potential energy is converted into kinetic energy and turbines rotate with greater speed.
- Moving turbines rotate the armature of the electric generator to produce electricity. Energy obtained from flowing water is known as hydroelectric energy.
Problems associated with energy production from flowing water.
- Hydroelectric power plants can be constructed only at a limited number of places.
- When dams are constructed a large land area gets submerged which may cause long term pollution of rehabilitation.
2. Explain the working of solar cooker with the help of a neat and labelled diagram.
Answer. A solar cooker is a device that uses solar power to cook food. The first known solar cooker was built by Horace de Saussure in 1767.
- Solar cooker are available in many designs of different shapes and sizes.
- A box type solar cooker is as shown in figure. The box is made up of a non – conducting material like plastic or fibreglass.
- The walls of the box are made thick with a linking of non – conducting material to prevent the loss of heat.
- The inner surface of the cooker is painted black which absorbs 98% of the incident solar radiation.
- It has a glass cover on the top which facilitates retention of heat inside the box.
- Food to be cooked is kept in shallow vessel which is placed in the inner box. The outer surfaces of the shallow vessel are also painted black.
- A plane mirror is hinged on the top of the box which is adjusted in such a way that maximum radiation is reflected into the enclosure.
- The temperature inside the solar cooker is about 1000C – 1400C when kept in the sun for two hours.
3. Explain the working of solar water heater with the help of a neat and labelled diagram.
Answer.
- A simple type of solar water heater used for domestic purpose mainly consists of two parts
i. An insulated storage tank
ii. A flat plate collector.
- In flat plate collector, copper pipes with it’s outer surface painted black are fixed in the form of a coil in a box. Bending of pipes helps to increase the surface area for heating.
- The insulated storage tank is connected to the flat plate collector by copper pipe. One end of the pipe is connected to the bottom of the tank while other end is connected to the bottom of the tank while other end is connected to the middle of the tank.
- A reservoir or storage tank is kept at a higher level. It is used to store cold water and is connected to the insulated storage water tank.
Working
1. The water in the flat plate collector continuously circulates through copper pipe absorbing solar radiation and gets heated up.
2. Once the water gets heated up it expands and it becomes lighter and rises to the top of the storage tank. Hot water is lighter and remains in the upper part of the tank. The hot water can be drawn through a tap.
3. Its place is taken by the cold water from the bottom of the reservoir tank.
4. Explain with diagram the working of a biogas plant.
Answer. Construction
- Biogas plant consists of a well like structure called as ‘Digester’ which contains slurry of animal waster and water.
- The digester is usually constructed well below the ground level.
- There are two pipes joined to the bottom. One is for feeding animal waste, slurry and other for taking out the used slurry called as sludge which comes out after fermentation.
- A dome shaped structure called ‘Dome’ with a valve floats over the slurry in the digester and serves as an outlet for biogas.
Working:
- In a digester the action of an anaerobic micro organism breaks down or decomposes the complex compound of biomass in the slurry, in the presence of water.
- This process takes place within few days and gases like methane, carbon dioxide, hydrogen and hydrogen sulphide are produced.
- This mixture of gases is supplied to consumer.
- As biogas contains 80% of methane it is excellent fuel and burns without producing smoke.
- The slurry which has lost biogas is called sludge. It is rich in nitrogenous and phosphatic compounds and can be used as an excellent fertilizer.
5. Explain the calorific value of fuels? Why hydrogen and alcohol could be best source of energy in future?
Answer. The heat liberated in joule on complete burning of one gram of fuel is expressed as it’s calorific value.
- Calorific value of hydrogen is the highest among the fuels (150kj/kg). Still it is not commonly used as a fuel due to its highly explosive nature.
- Safer and cheaper methods to use hydrogen as a fuel are being developed by the scientists.
- Ethanol (alcohol) is a biofuel produced from baggase and other starch material by fermentation. Its calorific value is 30J/kg. At present ethanol is mixed with petrol and used as auto fuel. Technology is being developed to use ethanol as a main fuel.
- Hence, hydrogen and alcohol could be the best conventional sources of energy in future to cope up with the energy crisis.
6. Explain calorific value of fuels? How is calorific value determined?
Answer. The heat liberated in joule on complete burning of one gram of fuel is expressed as it’s calorific value.
- The calorific value is determined by burning a known mass (m) of fuel.
- All the heat produced is utilised to heat known mass of liquid in a container.
- Loss of heat is kept to a minimum value.
- The quantity of heat produced by fuel is calculated by measuring the rise in temperature of liquid in a container.
- Let the heat produced by burning fuel of mass m, is completely used to heat water of mass m1 and copper calorimeter of mass m2.
If rise in temperature of water in the container is t, then the heat lost by the fuel is given by;
Q = m1 c1 t + m2 c2 t
Where c1 = Specific heat of water
c2 = specific heat of calorimeter.
Calorific value is expressed in Joule per gram (S.I. unit) and (C.G.S. unit)
Q8. Draw neat and labelled diagrams.
- Solar cooker
- Windmill
3. Solar water heater
4. Biogas plant.
