Q1. Which of the following statements is incorrect ?
(a) Entropy is a quantity introduced to give clear expression to the results of thermodynamics
(b) Change in entropy is defined as the ratio of the amount of heat taken up to the absolute temperature
(c) Change in entropy is directly proportional to the amount of heat taken up
(d) The entropy of a system is a measure of its degree of disorder
(UPSC Prelims 1986)
Answer: (c) Change in entropy is directly proportional to the amount of heat taken up
Explanation: Entropy change is defined as ΔS = Q/T, where Q is heat and T is temperature. It is not directly proportional to heat alone; temperature also plays a role. Hence, statement (c) is incorrect.
Q2. Which of the following is used in diesel engine ?
(1) Cylinder
(2) Spark Plug
(3) Piston
(a) 1, 2 and 3
(b) 1 and 2
(c) 2 and 3
(d) 1 and 3
(UPSC Prelims 1987)
Answer: (d) 1 and 3
Explanation: Diesel engines use cylinders and pistons for combustion, but they do not use spark plugs. Instead, they rely on compression ignition, where fuel ignites due to high pressure and temperature.