1. Name the major constituent of biogas. List three characteristics to prove it as an excellent fuel.

Solution

Methane Smokeless, leaves no residue, higher heat of combustion.

2. (a) What is solar cell panel? (b) Name any two elements that are used for making solar cell panels.

Solution

(a) Solar Cell Panel: A combined arrangement of a large number of solar cells that can deliver sufficient electricity for practical use. (b) Silicon, germanium

3. How were fossil fuels formed?

Solution

The dead plants and animals which were buried deep under the earth for millions of years got converted into fossil fuels like coal, petroleum and natural gas. This happens because of absence of oxygen, high pressure, heat and bacterial action.

4. State two limitations of solar energy.

Solution

 1) The solar energy reaches the earth’s surface in a diffused form. It has been estimated that the solar energy received in the upper atmosphere is 1.4 kW/m2. Thus, it is too small for doing useful work. 2) It is not available uniformly all the time and at all the places of the earth. It is more in the Equatorial Regions than in the Polar Regions.  

5. What are the disadvantages of using fossil fuels? Give two instances where solar cells are exclusively used as source of energy?

Solution

1. (i)Buring of coal or Petroleum Products lead to air pollution.    (ii)The oxides of C, N and S are released on buring fossil fuels as acidic oxides it leads to acidic rain         and affect water soil.    (iii)CO2, a green house gas, causes global warming. 2. Solar cells are used as (i) source of electricity in artificial satellites (ii) source of electricity in radio and wireless transmissions, at TV relay stations, traffic lights and    research centers.

6. List any three hazards of nuclear waste.

Solution

Most of the nuclear wastes are radioactive and emit radiations which are dangerous. (i) Human body can tolerate the absorption of radiations up to certain level only. Beyond the tolerance level, it can cause irrepairable damage to the cells and nuclei of the cells. (ii) It may cause cancer or death of human beings. (ii) Radiation may cause change in DNA or genes that may give deformation of organs in future generation.

7. (a) What is geothermal energy? (b) What are the advantages of wind energy?

Solution

(a) When underground water comes in contact with the hot spot, steam is generated. The steam trapped in rocks is routed through a pipe to a turbine and used to generate electricity. (b) (1) Environment friendly (2) Efficient source of renewable energy (3) Does not require recurring expenses for the production of electricity.

8. Mention the limitations in exploiting geothermal energy.

Solution

The limitations in exploiting geothermal energy are: (i) It is not available everywhere. (ii) Deep drilling in the earth to obtain geothermal energy is technically very difficult and expensive.

9. What are the two kinds of nuclear reactions? Define them.

Solution

Nuclear reactions are broadly classified as nuclear fission reaction and nuclear fusion reaction. Nuclear fission reaction: The process of splitting of a heavy nucleus into smaller nuclei when bombarded with a low energy neutron with the liberation of tremendous amount of energy is called nuclear fission. Nuclear fusion reaction: Nuclear fusion is a reaction in which two or more light nuclei combine to form a heavier nucleus releasing an enormous amount of energy. Nuclear fusion occurs at a very high temperature of the order of 107 kelvin.  

10. List any two disadvantages of using of biomass as a fuel.

Solution

(i) Produces smoke (ii) gives less heat energy

11. Differentiate between renewable and non-renewable sources of energy with one example for each.

Solution

Energy sources that can be regenerated are called renewable sources of energy. Eg : Solar energy. Energy sources that will get depleted some day are called non-renewable sources of energy. Eg : Fossil fuels

12. Write the principle of the windmill?

Solution

The blowing wind strikes across the blades of the windmill. The wind exerts a force on these blades and rotates it. This in turn rotates the turbine of the generator to generate electricity.

13. Why is it not possible to make use of solar cells to meet all our energy needs? State at least three reasons to support your answer.

Solution

(i) High cost of installation. (ii) Limited availability of special grade silicon to make solar cells. (iii) Unavailability of efficient system to store electrical energy generated by solar panels.

14. Give the composition of the slurry fed into the digester of a gobar gas plant.

Solution

Water and cow-dung.

15. Explain the principle underlying the working of a solar cell.

Solution

Solar cell is a device which directly converts solar energy into electrical energy. This principle is based on the phenomenon of photovoltaic effect. The Phenomenon due to which light energy directly changes into electrical energy, when light is incident on certain sensitive materials (semi conductors) is called photovoltaic effect.

16. Write the full form of CNG.

Solution

Compressed Natural Gas

17. Name the device that directly converts solar energy to electric energy.

Solution

Solar cell.

18. Explain what are fossil fuels?

Solution

Fossil fuels A natural fuel formed deep under the earth from the remains of living organisms is called fossil fuel. Fossil fuels are non-renewable sources of energy. Burning fossil fuels releases acidic oxides which are oxides of carbon, sulphur and nitrogen. This leads to acid rain which affects water and soil resources. The Sun is the source of fossil fuels. Sunlight makes plants live, and later, they are converted into fossil fuels.

19. What is a solar cell panel? Mention any three of its applications.

Solution

A solar cell panel is a combination (or array) of a large number of solar cells. Application – TV relay stations, artificial satellites, space probes, wireless transmission etc (any three correct)

20. You are given two solar cookers, one with a plane mirror as reflector and the other with concave   mirror as reflector. Which one is more efficient? Give reason for your answer. State one more use of concave mirror.

Solution

Solar cooker with concave mirror reflector is more efficient. Because concave mirror can focus the heat radiations to the material kept inside to increase the temperature. Concave mirror is used in headlight of vehicles or as shaving mirror.

21. Define: Ignition temperature.

Solution

The minimum temperature to which a fuel must be heated so that it may catch fire and start burning is called its ignition temperature.

22. List any two steps you would suggest to minimize environmental pollution caused by burning of fossil fuels?

Solution

(i) Use of smokeless appliances. (ii) Afforestation.

23. Suggest any two reasons which make the large scale usage of nuclear energy prohibitive.

Solution

High cost of installation High risk of environmental contamination  Limited availability of uranium

24. Name the various forms in which energy is available from the sea. For any two types give one limitation in harnessing.

Solution

The forms of energy that can be obtained from the ocean are tidal energy, wave energy, and ocean thermal energy. There are several limitations in order to harness these energies. (i) Tidal energy depends on the relative positioning of the Earth, Moon, and the Sun. (ii) High dams are required to be built to convert tidal energy into electricity. (iii) Very strong waves are required to obtain electricity from wave energy. (iv) To harness ocean thermal energy efficiently, the difference in the temperature of surface water (hot) and the water at depth (cold) must be 20o C or more. (Any two limitations)

25. List (i) any three advantages and (ii) any three limitations of using a solar cooker.

Solution

(i) (1) Pollution free (2) Economical (3) Nutrients of food are retained (ii) (1) Night/cloudy weather (2) Takes more time to cook food (3) Direction of solar cooker to be changed too often.

26. Write three limitations of harnessing three types of energy from Oceans.

Solution

(i) Wave energy be a viable proposition only when waves are very strong.  (ii) A tidal power station at the mouth of a river blocks the flow of polluted water into the sea. It creates health and pollution hazards. (iii) Efficient commercial exploitation is difficult or any other.

27. A group of farmers teamed together to set up a biogas plant close to their farms. List any six advantages that they would be able to derive from the plant.

Solution

(1) Waste disposal from farms (2) Efficient disposal of animal excreta (3) Biogas as fuel in chulhas (4) Manure for the farms (5) Biogas for lighting in the homes (6) Economical

28. Discuss the advantages and disadvantages of using solar cells.

Solution

Advantages of using Solar Cells:1) The source of energy for solar cell is present in abundance. 2) They have no moving parts, and hence reuire little maintenance and work uite satisfactorily without any focusing device. 3) They do not cause any environmental pollution like the fossil fuels and nuclear power. 4) Solar cells last a longer time and have low running costs. Disadvantages:1) The entire process of manufacture is very expensive 2) Also silver is used for interconnection of these cells in the panel, which is a very expensive metal. 3) A practical problem linked with the use of solar cell panels is regarding the storage of electricity general by them.

29. A student constructed a model of box type solar cooker. Instead of using glass sheet he used a transparent plastic sheet to cover the open face of the box. He found that this cooker does not function well. What could be the possible drawbacks in his model? Explain the advantage of painting black the inner and outer surfaces of the cooker and that of cooking vessels.

Solution

Glass sheet – prevents the escape of heat radiation from the box while plastic sheet does not possess this property. Black surfaces absorb heat radiation.

30. State two limitations of bio – gas plants.

Solution

1) The initial cost of installation is very high. 2) The number of cattle owned by an average family of farmers is inadequate to feed a biogas plant.

31. List any three limitations in harnessing wind energy.

Solution

(i) Wind energy farms can be set only at places where wind blows for a greater part of the year. (ii) Wind speed should be greater than 15 km/h. (iii) Require vast area of land to set up wind farm. (iv) Initial cost of establishment of wind farm is very high (any three)

32. Biogas is considered to be a boon to the farmers. Give reasons.

Solution

• Farmers can produce clean fuel from bio wastes • Spent slurry is used as a manure • Can be used to generate electricity • Can be used to run engines

33. (a) Charcoal is a better fuel than wood. Why? (b) How does biogas plant help to reduce the problem of pollution?

Solution

(a) Charcoal is a better fuel than wood because  (i) It has a higher heat generation efficiency than wood. (ii) It does not produce smoke when it is burnt, whereas wood produces a lot of smoke. (b) Biogas plant helps to reduce the problem of pollution because, large scale utilization of bio-waste and sewage materials provides safe and efficient method of waste disposal.

34. List any four qualities of an ideal source of energy.

Solution

(1) More heat per unit mass (2) Pollution/smoke free (3) Economical (4) Easily available (5) Easy to handle (6) Safe to transport (any four)

35. (a) Name any two exhaustible sources of energy. (b) Would you consider hydrogen to be a cleaner and more efficient fuel than CNG? If yes, why is it not used in everyday life?

Solution

(a) Coal and petroleum. (b) Yes, it is a cleaner fuel because on burning it, only water vapour is produced, which is non-polluting. But, due to explosive nature of hydrogen, its storage and transportation is difficult.

36. List any three ways in which construction of dams for production of electricity adversely affects the environment of that place.

Solution

The construction of dams for production of electricity adversely affects the environment of the place in the following ways: (i) Large areas of agricultural land and human habitation are to be sacrificed as they get submerged. (ii) Large eco-systems are destroyed when submerged under the water in dams. (iii) The vegetation which is submerged rots under anaerobic conditions and gives rise to large amounts of methane which is a green-house gas.

37. What are the factors that should be taken into consideration for selecting a source of energy? List any three.

Solution

(i) The ease and cost of extracting energy from the source. (ii) The efficiency of the technology available to extract energy from the source. (iii) The damages to the environment which will be caused by using that source.

38. Why is the box of a solar cooker covered with a glass plate?

Solution

The glass plate cover produces green house effect which helps to increase the temperature inside the box of the cooker.

39. Can any source of energy be pollution free? Why or why not?

Solution

No source of energy can be perfectly pollution free but biomass energy, hydro electric energy, wind energy, geothermal energy and solar energy are almost pollution free. If fossil fuel is allowed to burn in presence of excess of oxygen, the pollution produced can be reduced to a good extent.

40. How has the traditional use of wind and water energy been modified for our convenience?

Solution

(i) Wind energy has been modified by establishment of wind energy farm which generates electricity. (ii) Water energy has been modified by constructing high rise dams on the high altitude rivers to get electricity.