Question 1 The use of dry wood as domestic fuel is not considered as good. State two reasons for it. Solution
(a) It leads to deforestation which causes problems like floods, erosion of fertile land and environmental imbalance
(b) It causes a lot of smoke and pollution.
Question 2 What are the three disadvantages of burning fossil fuels? Solution
(i)Fossil fuels are formed under the earth’s surface by a long process which takes million years to form fossil fuel and there are only limited reserves.
(ii) Fossil fuels are non – renewable sources of energy.
(iii) Burning of fossil fuels causes air pollution. The oxides of carbon, nitrogen and sulphur that are released on burning fossil fuels cause acid rain and other respiratory problems for human beings.
Question 3 Name four sources of energy which are pollution free.
Question 4 Why is the solar cooker box covered with a plane glass plate? Solution
When sunlight falls over the solar cooker top, the sun rays pass through the glass sheet cover and get absorbed inside the cooker box.
This glass sheet covers does not allow the solar energy to flow out in the form of radiant heat.Thus it traps more and more heat rays of the sun thereby producing green house effect.That is why glass lid is used in the solar cooker.
any solar cells combined in an arrangement is called Solar cell panels. The solar cells in the solar panel are connected in such a that total potential difference and total capacity to provide electric current becomes large
Question 6 Construction of dams submerges large areas of forests. How does this contribute to the greenhouse effect?
Question 7 Write three different ways of harnessing energy from ocean. Solution
Question 8 Name the main constituent of biogas. and Name two combustible components of biogas. Solution
The two combustible components of biogas are methane (CH4) and hydrogen (H2).
Question 9 What steps can help minimize environment pollution caused by burning of fossil fuels?
Acid rains happens because burning of fossil fuels release oxides of carbon, nitrogen and sulphur in the atmosphere
Question 11 How has the traditional use of wind and water energy been modified for our convenience? Question 12 Write the characteristic features of the micro-organisms which help in the production of biogas in a biogas plant. Solution
These micro-organisms do anaerobic decomposition of slurry to form methane and other components of bio gas.
Question 13 Name four conventional sources of energy. Solution
Question 14 State the reason for calling fossil fuels as non-renewable source of energy. Solution
Fossils fuels are formed by degradation of natural substances which is extremely slow and takes millions of years for a natural substance to convert into fossil fuel.
The rate of consumption of the fossil fuels is far greater than that of its rate of formation which results into their fast depletion.
Hence they are called non-renewable resources.
Question 15 Name the major constituent in natural gas. Solution
Natural gas is primarily composed of methane, but also contains ethane, propane and heavier hydrocarbons.
Question 16 Name the kind of energy possessed by wind and the device used to harness of biogas.
Question 17 Blowing wind carries kinetic energy. Mention the two factors that causes winds to blow.
(a) Name any two devices used to harness solar energy.
(b) Name any one material used to make a solar cell and also mention the range of voltage produced by a typical cell. Solution
Solar cell and Solar cooker
Solar cell mainly made of the semiconductor material Silicon and gallium which absorb the sun light efficiently. On an average, They produce voltage range of 0.4-0.5V.
Question 19 Compare the energy produced during fission of a uranium atom with the energy produced with due to combustion of a carbon atom from coal. Solution
The fission of an atom of uranium produces 10 million times the energy produced by the combustion of an atom of carbon from coal
(a)Write any two advantages of using solar cells.
(b) Write the special technique used for mounting solar cell panels. Mention its advantages. Solution
(a)(i) These can be used anywhere as a self – generating source of electricity.
(ii) One constructed, there is no further cost of production or maintenance in such devices.
(b)The solar cell panels are mounted on specially designed inclined roof tops so that more solar energy is incident over it
Question 21 Name the process that takes place in a nuclear reactor designed for electric power generation. Solution
In Nuclear fission, A heavy nucleus is bombarded with a low energy neutron. In this process, it splits into two lighter nuclei with a tremendous release of energy which can be utilized to boil water to run turbines
Question 22 What are hot spots inside earth’s crust? Question 23 Explain the term ‘Hot Spots’ in the context of geothermal energy production. Question 24 Name any two nuclear fuels used for the process of nuclear fission. Solution
Uranium and plutonium
Question 25 Differentiate between renewable and non – renewable sources of energy with one example for each. Solution
Question 26 Explain why:
(i) Solar cooker are covered with glass plate.
(ii) The solar cooker is painted black from inside.
(iii) Out of two solar cookers one was covered by a plane glass slab and other was left open. Which of two solar cookers will be more efficient an Question 27 Write the general principle involved in generating nuclear energy? Name one fuel used in a nuclear reactor. Solution
Nuclear energy is generated through the process of Nuclear Fission. In Nuclear fission, A heavy nucleus is bombarded with a low energy neutron. In this process, it splits into two lighter nuclei with a tremendous release of energy which can be utilized to boil water to run turbines.Uranium is used as the fuel
Question 28 What kind of mirror concave, convex or plain would be best suited for use in a solar cooker? Why? Solution
A concave mirror would be best suited for use in a solar cooker because it reflect and focus the sunlight at a point. The temperature at that point increases which heats and cooks the food placed at that point.
Question 29 Write two advantages of classifying energy sources as renewable and non – renewable. Question 30 State any four characteristics of a good source of energy. Solution
A good source of energy has following characteristics:
(i)It could do a large amount of work per unit volume or mass.
(ii) It would be easily accessible.
(iii) it would be easy to store and transport.
(iv) It would be economical.