Physics Multiple Choice Questions on “Thermodynamics – Carnot Engine”.
1. Find work done by one mole of a gas in one cycle. V1 = 1m3, V2 = 4m3, V3 = 6m3, V4 =3m3. Temperature is given in °C.
a) 303Rln(4) J
b) 303Rln(2) J
c) 30Rln(2) J
d) 30Rln(4) J
Answer: b
Clarification: The given T-S diagram represents a carnot cycle.
Work done is given by:
nRT1ln(V2/ V1) – nRT4ln(V3/ V4)
= 293Rln(4) – 283Rln(2)
= 303Rln(2).
2. What is the correct order of steps for a carnot cycle?
a) Isothermal expansion, adiabatic expansion, isothermal compression, adiabatic compression
b) Isothermal compression, adiabatic expansion, isothermal expansion, adiabatic compression
c) Adiabatic compression, adiabatic expansion, isothermal expansion, isothermal compression
d) Adiabatic compression, isothermal expansion, adiabatic expansion, isothermal compression
Answer: a
Clarification: A carnot cycle is a reversible cyclic process having the maximum possible efficiency. The steps of the cycle are: isothermal expansion of gas, adiabatic expansion, isothermal compression and then adiabatic compression. This is evident from its PV diagram: