CBSE Class 10 Science 2020 · Paper 31/C/1 · Question 4
Answer question numbers 4(a) – 4(d) on the basis of your understanding of the following paragraph and the related studied concepts :
There are different forms of energy and one form of energy can be converted into another. When we light a wax candle, the process is highly exothermic and on burning, the chemical energy of the wax gets converted into heat and light. A good source of energy is to be selected for the choice of work to be done. In ancient times, wood was the most common source of heat energy. We, in our daily lives, use various energy sources for doing the work. Nowadays we use diesel and electricity to run trains. We also use fossil fuels in vehicles which has some serious disadvantages, mainly air pollution. The recent example of air pollution was ‘Smog’ in the National Capital Region of Delhi. This pollution was a result of burning ‘Parali’ in northern states of the country, which affected the eyes and also caused serious respiratory problems.
- (a)State the energy conversion that takes place when we light a wax candle.[1]
- (b)List two criteria of selecting a source of energy for a specific work.[1]
- (c)Write the names of two fossil fuels.[1]
- (d)Why are we looking at alternate sources of energy ?[1]
Answer
Chemical energy becomes heat and light; coal and petroleum are fossil fuels; fossil fuels run out and pollute, so renewable, cleaner sources are needed.
(a) The chemical energy stored in the wax is converted into heat energy and light energy.
(b) Any two of: it should do a large amount of work (give a large amount of heat) per unit mass or volume; it should be easily accessible; it should be easy to store and transport; it should be economical (and cause little pollution).
(c) Coal and petroleum (natural gas is another).
(d) Fossil fuels are non-renewable, and their limited reserves will be exhausted; burning them also causes air pollution (acid rain and greenhouse gases). So we look for alternate sources that are renewable and cleaner.
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