Question 1: Name a non-renewable source of energy other than fossil fuels.
Solution : Nuclear fuels (like uranium)
Question 2: Define calorific value of a fuel.
Solution : The amount of heat produced by burning 1 gram of a fuel completely is known as its calorific value.
Question 3: “The calorific value of cooking gas (LPG) is 50 kj/g”. What does it mean ?
Solution : Calorific value of LPG is 50kJ/gm means that if 1 gram of LPG is burnt completely, then it will produce 50kJ of heat energy.
Question 4: Which of the following produces more heat (per unit mass) on burning ?
Coal or LPG
Solution : LPG, due to its higher calorific value.
Question 5: Define ignition temperature of a fuel.
Solution : Ignition temperature of fuel can be defined as the minimum temperature to which a fuel must be heated so that it may catch fire and start burning.
Question 6: “The ignition temperature of a fuel is 80°C”. What does this mean ?
Solution : If ignition temp of a fuel is 80oC, this means that minimum 80oC is required for the ignition of the fuel.
Question 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.
Solution : calorific.
Question 8: What is a source of energy ? What are the two main categories of the sources of energy ?
Solution : A source of energy is one which can provide adequate amount of energy in a convenient form over a long period of time.
Two main categories of the source of energy are:
i. Renewable source of energy
ii. Non- renewable source of energy
Question 9: State any four characteristics of a good source of energy.
Solution : A good source of energy is one:
(i) which would do a large amount of work per unit mass,
(ii) which is cheap and easily available,
(iii) which is easy to store and transport,
(iv) which is safe to handle and use.
Question 10: What is meant by a non-renewable source of energy ? Give two examples of non-renewable sources of energy.
Solution : A non-renewable source of energy is defined as the source of energy which has accumulated in nature over a very, very long time and cannot be quickly replaced when exhausted.
Ex. Coal, petroleum etc.
Question 11: What is meant by a renewable source of energy ? Give two examples of renewable sources of energy.
Solution : A renewable source of energy is the one which is being produced continuously in nature and is inexhaustible.
Ex. wind energy, ocean thermal energy etc.
Question 12: What is the difference between a renewable and a non-renewable source of energy ? Explain with examples.
Solution : Renewable source of energy can be used again and again endlessly, where as non-renewable source of energy cannot be renewed once used.
Ex. Renewable sources of energy are wind energy, ocean energy.
Non-renewable sources of energy are coal, fossil fuel.
Question 13: Why are fossil fuels classified as non-renewable sources of energy ?
Solution : Fossil fuels are known as non-renewable sources of energy because fossil fuels once used cannot renewed or regained.
Question 14: Name two sources of energy that you think are renewable. Give reason for your choice.
Solution : Air and water, because both air and water can be used again and again endlessly, they never get exhausted.
Question 15: Name two sources of energy which you consider to be non-renewable. Give reason for your choice.
Solution : Petroleum and coal are non-renewable sources of energy because they cannot be used again once exhausted.
Question 16: (a) Classify the following into renewable and non-renewable sources of energy :
Coal, Wind, Tides, Petroleum, Wood, Natural gas
(b) What is the basis of above classification ?
Solution : (a) Renewable source of energy – wind, tides, wood
Non- Renewable source of energy – coal, petroleum, natural gas
(b) The above classification is based on the fact that renewable sources are inexhaustible, whereas non-renewable sources are exhaustible.
Question 17: Coal is said to be formed from the wood of trees. Why then is coal considered to be a non-renewable source of energy whereas wood is a renewable source of energy ?
Solution : Coal is a non-renewable source of energy because it has accumulated in the earth over a very. very long time, and if all the coal gets exhausted, it cannot be produced quickly in nature.
Wood is considered as a renewable source of energy because if trees are cut to obtain wood, then more trees will grow in due course of time.
Question 18: (a) What is a fuel ? Give five examples of fuels.
(b) What are the characteristics of an ideal fuel (or good fuel) ?
(c) The calorific value and ignition temperature of fuel A are 55 kj/g and 80°C, respectively. These values for fuel B are 80 kj/g and 10°C, respectively. On burning, the fuel A produces C02 and H20 while the fuel B produces C02, CO and S02 . Give three points of relative advantages and disadvantages of these two fuels.
Solution : (a) The material which is burnt to produce heat energy is known as a fuel.
Ex. Wood, coal, LPG, kerosene, diesel etc.
(b) Characteristics of ideal fuel:
(i) It should have high calorific value.
(ii) It should burn without giving out any smoke or harmful gases.
(iii) It should have proper ignition temperature.
(iv) It should cheap and easily available.
(c) Fuel A:
i. Lower calorific value of 55 kJ/g (Disadvantage)
ii. Moderate ignition temperature of 80oC (Advantage)
iii. No harmful gases produced (Advantage)
i. High calorific value of 80 kJ/g (Advantage)
ii. Very low ignition temperature of 10oC (Disadvantage)
iii. Harmgul gases like CO and SO2 produced (Disadvantage)
Question 30: The calorific values of three fuels A, B and C are 33 kj/g, 48 kj/g and 150 kj/g, respectively. A is solid, B is liquid and C is a gas at room temperature. On combustion, both A and B produce 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 ?
Solution : Fuel B is the most ideal fuel because.
(i) it leaves no residue on burning.
(ii) it has high calorific value of 48 kJ/g.
(iii) it does not burn explosively.
Question 31: Calorific value and ignition temperature of fuel X are 75 kj/g and 20°C respectively. These values for fuel Y are 50 kj/g and 75°C respectively. On burning, the fuel Y produces only CO2 while fuel X produces CO2 and CO. Which of the two is a better fuel ?
Solution : Fuel Y is a better fuel because
(i) it has a moderate ignition temperature of 75oC.
(ii) it produces no harmful gases like CO on burning.
Question 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. 30 kj/g
Which of the fuels could be : (i) cooking gas (ii) alcohol (iii) wood (iv) hydrogen (v) kerosene ?
Solution : (i) cooking gas – D
(ii) alcohol – E
(iii) wood – B
(iv) hydrogen – C
(v) kerosene – A
Question 33: Arrange the following fuels in the order of decreasing calorific values (keeping the fuel with highest calorific value first) :
Biogas, Kerosene, Wood, Petrol, Hydrogen gas, Methane
Solution : Hydrogen gas>Methane>Petrol>Kerosene>Biogas>Wood
Question 34: Arrange the following fuels in the order of increasing calorific values (keeping the fuel with lowest calorific value first) :
LPG, Coal, Alcohol, Dung cakes, Diesel
Solution : Dung cakes<Coal<Alcohol<Diesel<LPG
Question 35: Most of the fuels contain carbon as one of the constituents. Name a fuel which has very high calorific value but does not contain carbon.
Solution : Hydrogen gas.