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Q 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.
Q 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
Q 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.
Q 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.
Q 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.
Q 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.
Q 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.
Q 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.
Q 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.
Q 10. List any two disadvantages of using of
biomass as a fuel.
Solution
(i) Produces smoke (ii) gives less heat energy
Q 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
Q 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.
Q 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.
Q 14. Give the composition of the slurry fed
into the digester of a gobar gas plant.
Solution
Water and cow-dung.
Q 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.
Q 16. Write the full form of CNG.
Solution
Compressed Natural Gas
Q 17. Name the device that directly converts
solar energy to electric energy.
Solution
Solar cell.
Q 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.
Q 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)
Q 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.
Q 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.
Q 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.
Q 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
Q 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)
Q 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.
Q 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.
Q 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
Q 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 reQ uire little maintenance and work Q 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.
Q 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.
Q 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.
Q 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)
Q 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
Q 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.
Q 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)
Q 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.
Q 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.
Q 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.
Q 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.
Q 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.
Q 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.
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