## Solutions of Sources of Energy- Lakhmir Singh Manjit Kaur VSAQ, SAQ, LAQ and MCQ Pg No. 121 Class 10 Physics

1. Name a non-renewable source of energy other than fossil fuels.

→ The nuclear fuels like nuclear fuels are the non renewable sources of energy other than fossil fuels.

2. Define calorific value of a fuel.

→ Calorific value of a fuel can be defined as the amount of heat produced by the combustion of 1 gram of that fuel completely.

3. “The calorific value of cooking gas (LPG) is 50 kj/g”. What does it mean?

→ Since Calorific value is the amount of heat produced by burning a unit of the fuel completely, hence, calorific value of LPG is 50kJ/gm means that if 1 gram of LPG is burnt completely, then 50kJ of heat energy will be produced.

4. Which of the following produces more heat (per unit mass) on burning? Coal or LPG

→ Since LPG has a higher calorific value than coal, hence, LPG produces more heat on burning.

5. Define ignition temperature of a fuel.

→ The lowest temperature at which a combustible substance when heated catches fire in air and continues to burn is called ignition temperature.

6. “The ignition temperature of a fuel is 800 C”. What does this mean?

→ The ignition temperature of a fuel is 800 C means that 800C is the minimum temperature at which the particular fuel will catch fire or will ignite.

7. Fill in the following blank with a suitable word:
The amount of heat produced by burning a unit mass of a fuel completely is known as its---value.

→ Calorific value

8. What is a source of energy? What are the two main categories of the sources of energy?

→ A source of energy is one which can provide appropriate amount of energy in expedient form over a long period of time.
Two main categories of the source of energy are:
a) Renewable source of energy-source of energy that is not depleted when used. Such as wind or solar power.

b) Non- renewable source of energy-sources of energy that will run out or will not be replenished in our lifetimes or even in many, many lifetimes.

9. State any four characteristic of good sources of energy.

→ A good source of energy should have the following characteristics:
a) It should do a large amount of work per unit mass or volume that means it should have high calorific value.
b) It should be easily accessible and provide energy over a long period of time. Example: coal and petroleum.
c) Should be easy to store and transport.
d) Safe and convenient to use - energy sources should be safe as it is used by a large number of people and should be convenient.

10. What is meant by a non-renewable source of energy? Give two examples of non-renewable sources energy.

→ Non-renewable source of energy is one that will run out or will not be replenished in our lifetimes or even in many, many lifetimes. Most non-renewable energy sources are fossil fuels: coal, petroleum, and natural gas.

11. What is meant by a renewable source of energy? Give two examples of renewable sources of energy.

→ Renewable source of energy are those sources that generate energy from natural resources – such as sunlight, wind, rain, tides and geothermal heat – which are renewable (naturally replenished). Hence, they do not deplete with time.

12. What is the difference between a renewable and non-renewable source of energy? Explain with examples.

→ Renewable energy resources: The energy resources which cannot be exhausted and can be used again and again are called renewable energy resources. For example solar energy, wind energy, tidal energy and hydroelectric etc.
Non-renewable energy resources: The energy resources which can be exhausted one day and cannot be used repeatedly are called non-renewable energy resources. The example of non-renewable energy resources are coal, petroleum, natural gases etc.

13. Why are fossil fuels classified as non-renewable sources of energy?

→ Fossil fuels are non-renewable because they take millions of years to form. Fossil fuels make up most sources of non-renewable energy, and they were created millions of years ago as a result of marine creatures decaying under immense pressure and heat.

14. Name two sources of energy that you think are renewable. Give reason for your choice.

→ Solar energy, wind energy, ocean energy etc., are renewable sources of energy due to the following reasons:
a) These forms of energy are available in plenty in our natural environment in the form of continuous currents of energy.
b) These energy sources will not be depleted because their supply is large and extraction of usable energy from these sources is negligible.

15. Name two sources of energy which you consider to be non-renewable. Give reason for your choice.

→ Two examples of non renewable sources are-
a) Coal: It is produced from dead remains of plants and animals that remain buried under the earth's crust for millions of years. It takes millions of years to produce coal. Industrialization has increased the demand of coal. However, coal cannot replenish within a short period of time. Hence, it is a non-renewable or exhaustible source of energy.
b) Wood: It is obtained from forests. Deforestation at a faster rate has caused a reduction in the number of forests on the Earth. It takes hundreds of years to grow a forest. If deforestation is continued at this rate, then there would be no wood left on the Earth. Hence, wood is an exhaustible source of energy.

16A. Classify the following into renewable and non-renewable sources of energy:
Coal, Wind, Tides, Petroleum, Wood, Natural gas.

→ Renewable source of energy - wind, tides, wood.

16B. Non- Renewable source of energy - coal, petroleum, natural gas.

→ The above classification is based on the fact that renewable sources are inexhaustible, whereas non-renewable sources are exhaustible.

17. Coal is said to be formed from the wood of trees. Why then is coal considered to be a non-renewable sources of energy whereas wood is a renewable sources of energy?

→ Coal is considered to be a non-renewable source of energy whereas wood is a renewable source of energy because coal is formed when dead plants got buried under the earth for a long period of time. It took millions of years to be replenished. So coal is considered to be non renewable source of energy.

18A. What is a fuel? Give five examples of fuels.

→ A fuel is a substance which is burn to produce heat energy. Wood, Coal, LPG, Diesel are some common examples of fuel.

18B. What are the characteristics of an ideal fuel (or good fuel)?

→ The characteristics of an ideal fuel are:
It must have high calorific value.
It must burn without releasing any smoke or toxic gases.
It need to have proper ignition temperature.
It should be inexpensive and easily accessible.

18C. The calorific value and ignition temperature of fuel A are 55 kJ/g and 80oC, respectively. These values for fuel B are 80 kJ/g and 10°C, respectively. On burning, the fuel A produces CO2 and H2O while the fuel B produces CO2, CO and SO2. Give three points of relative advantages and disadvantages of these two fuels.

→ Fuel A:
No toxic gases are released.
Proper ignition temperature of around 80°C.
It has a lower calorific value of 55kJ/g.
Fuel B:
It has a high calorific value of 80kJ/g.
It releases toxic gases like CO and SO2.
It has a very low ignition temperature of 10°C.

Multiple Choice Questions (MCQs)-Pg-122

19. An example of a renewable sources of energy is :
A. Petrol
B. natural gas
C. Bio-gas
D. kerosene

→ As it is prepared from the animal dung, vegetable waste, etc.

20. A non-renewable sources of energy is:
A. Wood
B. alcohol
C. hydrogen gas
D. natural gas

→ As it is a fossil fuel.

21. Which of the following is not a renewable sources of energy?
A. wind
B. flowing water
C. fossil fuels
D. fuel wood

→ As they take millions of years to be replenished again hence, considered non-renewable source of energy.

22. A good fuel is one which process :
A. high calorific value and low ignition temperature
B. high calorific value and high ignition temperature
C. high calorific value and moderate ignition temperature
D. low calorific value and moderate ignition temperature

→ As it is the quality of an idle fuel.

23. The fuel having a calorific value of 55 kJ/g is likely to be :
A. bio gas
B. methane gas
C. hydrogen gas
D. natural gas

→ It is present as a major component in biogas.

24. A newly planted sapling usually grows and matures into a tree in more than:
A. 50 years
B. 25 years
C. 45 years
D. 15 years

→ A sapling is a tree seedling that has grown sufficiently to be planted in a Tree Patch.

25. Which of the following fuels has the high calorific value ?
A. natural gas
B. methane gas
C. hydrogen gas
D. bio gas

→ Hydrogen has a calorific value of 15000Kj/kg.

26. The fuel having the lowest calorific value is?
A. coal
B. wood
C. charcoal
D. kerosene

→ Calorific value of wood in dry state 3500kj/Kg and natural state 1500kj/Kg.

27. There are four fuels which all contain only carbon and hydrogen. The fuel having highest calorific value will be one which has:
A. more of carbon but less of hydrogen
B. less of carbon but more of hydrogen
C. equal proportions of carbon and hydrogen
D. less of carbon as well as less of hydrogen

→ As carbon has a low calorific value so it would decrease the calorific value of the fuel if present in more amount, whereas Hydrogen has high calorific value so it would increase the calorific value of the fuel if present in excess.

28. One of the following is not a characteristic of a good fuel. This is:
A. high calorific
B. no emission of smoke
C. smooth burning
D. high ignition temperature

→ A Good fuel require low or at least moderate ignition temperature.

29. Which of the following is not a fossil fuel?
A. coal
B. petroleum gas
C. biogas
D. Natural gas

→ This is because Biogas isn't prepared from the remains of plants and animals whereas fossils fuels are prepared from the remains of plants and animals.

Questions Based on High Order Thinking Skills (HOTS)-Pg-123

30. The calorific values of three fuels A, B and C are 33 KJ/g, 150 KJ/g, respectively. A is solid, B is liquid and C is a gas at room temperature. On combustion, both A and B produces carbon dioxide while C explodes forming steam. B and C leave no residue after combustion while A leaves behind some solid residue. Which one of the three fuels is the most ideal? Give two reasons to support your answer.

→ Fuel B is the most ideal fuel due to the following main reasons:
(i) As it leaves no reside on burning like the other two.
(ii) As an idle fuel it has a high calorific value of 48 KJ/g.

(iii) Moreover it does not burn explosively.

31. Calorific value and ignition temperature of fuel X are 75 kJ/g and 200C respectively. These values for fuel Y are 50 kJ/g and 750C respectively. On burning, the fuel Y produces only CO2 while fuel X produces CO2 and CO. Which of the two is a better fuel? Give two reasons to support your answer.

→ Fuel Y is a better fuel due to the following main reasons:
(i) Y has a moderate ignition temperature of 75°C
(ii) As it do not produce any harmful gas (like CO) while burning.

32. The calorific values of five fuels A, B, C, D and E are given below:
(A) 48 kJ/g
(B) 17 kJ/g
(C) 150 kJ/g
(D) 50 kJ/g
(E) 30kJ/g
Which of the fuels could be: (i) cooking gas (ii) alcohol (iii) wood (iv) hydrogen (v) kerosene ?

→ (i) D (calorific value of cooking gas)
(ii) E (calorific value of alcohol)
(iii) B (calorific value of wood)
(iv) C (calorific value of Hydrogen)
(v) A (calorific value of kerosene)

33. Arrange the following fuels in the order of decreasing calorific values (keeping the fuels with highest calorific value first):
Biogas, Kerosene, Wood, Petrol, Hydrogen gas, Methane.

→ Hydrogen gas>Methane> Petrol > Kerosene > Biogas > Wood
Hydrogen has the highest calorific value where as wood has the lowest calorific value.

34. Arrange the following fuels in order of increasing calorific values (keeping the fuels with lowest calorific value first):
LPG, Coal, Alcohol, Dung cakes, Diesel.