Thermodynamics Multiple Choice Questions on “Temperature-Entropy Plot”.
1. For a reversible heat transfer and process being adiabatic, which of the following is true?
a) dQ=0
b) dS=0
c) S=constant
d) all of the mentioned
Answer: d
Clarification: dQ=0 since process is reversible and adiabatic and dS=dQ/T.
2. A reversible adiabatic process is an isentropic process.
a) true
b) false
Answer: a
Clarification: dQ=0 and dS=0 and hence S=constant.
3. The area under the curve ∫TdS is equal to the
a) work done
b) heat transferred
c) internal energy change
d) none of the mentioned
Answer: b
Clarification: Q(reversible)=∫TdS.
4. Which of the following statement is true?
a) for reversible isothermal heat transfer, Q=t(Sf-Si)
b) for reversible adiabatic process, S=constant
c) both of the mentioned
d) none of the mentioned
Answer: c
Clarification: For reversible isothermal heat transfer, T=constant and for reversible adiabatic process, dS=0.
5. A Carnot cycle has following processes.
a) 4 reversible isotherms
b) 4 reversible adiabatics
c) 2 reversible isotherms and 2 reversible adiabatics
d) none of the mentioned
Answer: c
Clarification: Two reversible isotherms and two reversible adiabatics constitute a Carnot cycle.
6. Net work in a Carnot cycle is given by (T1=temperature of heat addition and T2=temperature of heat rejection)
a) (T2-T1)(S1-S4)
b) (T1-T2)(S1-S4)
c) (T1-T2)(S4-S1)
d) none of the mentioned
Answer: b
Clarification: Net work=Q1-Q2=(T1-T2)(S1-S4).
7. According to the principle of Caratheodory, the first law in differential form is written as dQ=Adx+Bdy+Cdz.
a) true
b) false
Answer: a
Clarification: Here, x,y,z are the three thermodynamic coordinates and A,B,C are the functions of x,y,z.
8. For adiabatic, reversible transition,
a) Adx+Bdy+Cdz=-1
b) Adx+Bdy+Cdz=1
c) Adx+Bdy+Cdz=0
d) none of the mentioned
Answer: c
Clarification: dQ=Adx+Bdy+Cdz=0 for adiabatic and reversible process.
9. For quasi-static, adiabatic path
a) Adx+Bdy+Cdz=TdS
b) Adx+Bdy+Cdz=1
c) Adx+Bdy+Cdz=0
d) none of the mentioned
Answer: a
Clarification: This comes from Caratheodory’s theorem.
10. The infinitesimal change in entropy dS due to reversible heat transfer dQ at temperature T is dS=dQ/T.
a) true
b) false
Answer: a
Clarification: For a reversible process, dS=dQ/T .