Solutions of Sources of Energy (Page No- 123) - Physics By Lakhmir Singh, Class 10 | Extra Documents, Videos & Tests for Class 10 PDF Download

Lakhmir Singh Physics Class 10 Solutions Page No:123

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 75^oC.
(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.