Intext Questions Solved

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Question 1 : What is a good source of energy?

Answer : A good source of energy would be one
i) which could do a large amount of work per unit volume or mass.
ii) which would be easily accessible.
iii) be easily be transported and stored.
iv) be economical.

Question 2 : What is a good fuel?
i) has a very high calorific value.
ii) does not produce a lot of smoke on burning.
iii) has easy availability.
iv) is cheap
v) has ignition temperature will above normal temperature.

Question 3 : If you could use any source of energy for heating your food, which one would you use and why?

Answer : We would not use any source of energy for heating your food, we would use that source of energy which would heat our food uniformly keeping its nutritional value intact.

Page 248

Question 1 : What are the disadvantages of fossil fuels?

Answer : i) Fossil fuels cause air pollution.
ii) The oxides of nitrogen and sulphur are acidic which leads to acid rain.
iii) Carbon dioxide gas produces green house effect.
iv) Fossil fuels are non-renewable source of energy.

Question 2 : Why are we looking at alternate sources of energy?

Answer : Because todays most common sources of energy ‘fossil fuels’ are fast depleting. It we keep using these sources of energy at this rate there will be no fossil fuel, left for future generation. That is why we have to conserve fossil fuels and look for alternate source of energy.

Question 3 : How has the traditional use of wind and water energy been modified for our convenience?

Answer : The traditional use of wind energy is modified to wind mills and wind farms. Also the traditional use of water has been modified to power generation by hydroelectric power plant.

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Question 1 : What kind of mirror – concave, convex or plain – would be best suited for use in the solar cooker? Why?

Answer : A concave mirror is best suited for use in a solar cooker, as a concave mirror concentrate sun-ray form a large area to a small area.

Question 2 : What are the limitations of the energy that can be obtained from the oceans?

Answer : Limitation of energy obtained form oceans are
i) there are limited locations where dams can be constructed to harness tidal energy.
ii) energy from wave can be harnessed only if waves are very strong also equipment to trap wave energy are expensive.
iii) Efficiency of ocean thermal energy power plants is very low.

Question 3 : What is geothermal energy?

Answer : The energy obtained from hot molten rocks beneath the earth’s surface is called geothermal energy.

Question 4 : What are the advantages of nuclear energy?

Answer : Advantages of nuclear energy are
i) small amount of fuel produces tremendous amount of energy.
ii) in nuclear power plant once critical stage is reached than it can operate for long time without the need for refuelling.

Question 5 : Can you source of energy be pollution-free? Why or why not?

Answer : No source of energy can be pollution free but the degree of pollution may vary.

Question 6 : Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not?

Answer : Yes, hydrogen is a cleaner fuel than CNG because hydrogen produces water on burning whereas CNG produces CO2 on burning.

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Question 1 : Name two energy sources that you would consider to be renewable. Give reasons for your choices.

Answer : i) Energy from water and (ii) Solar energy.

Water can be used again and again as we have in water cycle. Similarly energy from the Sun is in abundance which would last millions of years that is why water and solar energy are renewable sources of energy.

Question 2 : Give the names of two energy sources that you would consider to be exhaustible. Give reasons for your choices.

Answer : i) Petrol and ii) Coal
Petrol and coal are available in limited amount, if we keep using these at present rate then sooner future generations will not have any petrol or coal for their use.

Text Book Questions Solved

Question 1 : A solar water heater cannot be used to get hot water on

a) a sunny day
b) a cloudy day
c) a hot day
d) a windy day

Answer : (b) a cloudy day.

Question 2 : Which of the following is not an example of a biomass energy source?

a) Wood
b) Gobar gas
c) Nuclear energy
d) Coal

Answer : (c) Nuclear energy.

Question 3 : Most of the sources of energy we use represent stored solar energy. Which of the following is not ultimately derived from the Sun’s energy?

a) Geothermal energy
b) Wind energy
c) Nuclear energy
d) Bio-mass

Answer : Nuclear energy.

Question 4 : Compare and contrast fossil fuels and the Sun as direct sources of energy.

Answer :

Fossil Fuels Sun
Fossil fuels are non-renewable sources of energy. Fossil fuels will last only few decades. The sun has been radiating enormous amount of energy for nearly 5 billion years and will continue radiating for another five billion years.
Fossil fuels were formed over million years ago indirectly from the energy of the sun. The sun is renewable source of energy.
Burning of fossil fuel causes pollution in the form of harmful gases and ashes. The energy from the sun is clean and almost free of cost.

Question 5 : Compare and contrast bio-mass and hydroelectricity as sources of energy.

Answer :

Biomass Hydroelectricity
Energy from biomass is produced from plant and animal products. It is produced by transforming kinetic energy of flowing water of river into electricity.
These do not produce much heat on burning and lot of smoke is produced along with heat. It does not cause any pollution.
But biogas is an excellent fuel containing 75% methane. For production of hydroelectricity construction of big dams are required due to which large areas of agricultural land and human habitation are submerged.

Question 6 : What are the limitations of extracting energy from

a) the wind?
b waves?
c) tides?

Answer :

(a) Limitations of extracting energy from wind
i) It is not available all the time.
ii) It is not available at all the places.
iii) Establishment of wind energy farms require large area of land and it also has high cost of construction.

b) Limitations of extraction energy from waves:
i) There are only few places where sea wave energy can be harnessed economically.

c) Limitations of extracting energy from tides:
i) Rise and fall of water is not enough to produce electricity on a commercial scale.
ii) There are only few sites suitable to build dams and harness kinetic energy.

Question 7 : On what basis would you classify energy sources as
a) renewable and non-renewable?
b) exhaustible and inexhaustible?

Are both the options given (a) and (b) the same?

Answer : Both (a) and (b) options are same.

Renewable/Inexhaustible Non-renweable/Exhaustible
1. They are also called inexhaustible. They are called as exhaustible.
2. The energy source that will not finish and can be renewed or made again is called renewable source of energy e.g. sun, water, water. The energy source that will finish and will get exhausted and cannot be made very soon or takes millions of years for its formation e.g., fossil fuels-petrol, coal.

 Question 8 : What are the qualities of an ideal source of energy?

Answer : 

  1. It should provide adequate amount of net energy?
  2. It should provide desired amount of energy at a constant rate over a long period of time.
  3. It should be convenient to use.
  4. It should easily be transported and stored.

Question 9 : What are the advantages and disadvantages of using a solar cooker? Are the places where solar cookers would have limited utility?

Answer :

Advantages of a Solar Cooker

  1. It saves fuel.
  2. It does not cause pollution.
  3. Nutrients of foods are not destroyed as temperature is not very high.
  4. Three or four items can be cooked at the same time.

Limitations of a Solar Cooker

  1. It cannot be used during night.
  2. On a cloudy day, it cannot be used.
  3. The direction of the reflector has to be adjusted according to the position of the sun.
  4. It cannot be used for making ‘chappatis’.
  5. It cannot be used for frying.

Question 10 : What are the environmental consequences of the increasing demand for energy ? What steps would you suggest to reduce energy consumption?

Answer : 

i) Contamination of air and water.
ii) Due to the production of greenhouse gases global warming taking place.
iii) Depletion of ozone layer.

Steps to reduce energy consumption:
i) Use of car-pools instead of using individual vehicles.
ii) Switching of lights when not in use.
iii) Using solar-cookers, solar-water heaters, etc.
iv) Using cycle for commuting nearby places.