Thermodynamics Multiple Choice Questions on “Quality of Energy”.
1. A hot gas flowing through a pipeline can be considered as a
a) reversible process
b) irreversible process
c) both of the mentioned
d) none of the mentioned
Answer: b
Clarification: The process given here is irreversible.
2. For an infinitesimal reversible process at constant pressure,
a) dS=m*dT/T
b) dS=Cp*dT/T
c) dS=m*dT/T
d) dS=m*Cp*dT/T
Answer: d
Clarification: Here m is the mass of gas flowing, Cp is its specific heat, and T is the gas temperature.
3. Adequate insulation must be provided for high temperature fluids.
a) true
b) false
Answer: a
Clarification: This is done to prevent heat loss which would be high at high temperatures.
4. The loss of exergy is more when,
a) the heat loss occurs at a higher temperature
b) the heat loss occurs at a lower temperature
c) depends on the process
d) none of the mentioned
Answer: a
Clarification: Higher the temperature, more will be the exergy loss.
5. The exergy of a fluid at a higher temperature is ___ than that at a lower temperature and ___ as the
temperature decreases.
a) less, increases
b) more, increases
c) more, decreases
d) less, decreases
Answer: c
Clarification: Higher is the temperature, higher will be the exergy and it decreases as the temperature decreases.
6. The second law affixes a quality to energy of a system at any state.
a) true
b) false
Answer: a
Clarification: For example we can say that the quality of energy of a gas at say 1000K is superior to that
at say 300K.
7. The available energy of a system ___ as its temperature or pressure decreases and approaches that of
the surroundings.
a) increases
b) decreases
c) remains constant
d) none of the mentioned
Answer: b
Clarification: As temperature decreases, exergy decreases.
8. At ambient temperature, exergy of the fluid is
a) neagtive
b) positive
c) infinity
d) zero
Answer: d
Clarification: As the temperature of fluid decreases, its exergy decreases adn when the temperature reaches ambient temperature, its exergy becomes zero.
9. Which of the following is true?
a) the first law states that the energy is always conserved quantity-wise
b) the second law states that the energy always degrades quality-wise
c) both of the mentioned
d) none of the mentioned
Answer: c
Clarification: Energy is always conserved according to first law but its quality is degraded.
10. If the first law is the conservation of energy, then the second law is called the law of degradation of
energy.
a) true
b) false
Answer: a
Clarification: Though energy is always conserved but its quality is always degraded.
11. When a gas is throttled adiabatically from a high to a low pressure,
a) the enthalpy remains same
b) there is degradation of energy
c) both of the mentioned
d) none of the mentioned
Answer: c
Clarification: This is because of the fact that energy always degrades quality-wise.
12. The ___ in entropy in an irreversible change is a measure of the extent to which energy ___ in that
change.
a) decrease, degrades
b) increase, degrades
c) increase, increases
d) decrease, increases
Answer: b
Clarification: Also, to get maximum work from a system, changes must be performed in a reversible manner.
13. If two bodies were allowed to reach thermal equilibrium, one by heat conduction and other by operating a Carnot engine between them and extracting work, the final equilibrium temperatures would
be different.
a) this is because of the lower value of the total internal energy
b) this is because of the higher value of the total internal energy
c) both of the mentioned
d) none of the mentioned
Answer: a
Clarification: Work is done at the expense of internal energy.
14. Adequate insulation is not that important for low temperature fluids.
a) true
b) false
Answer: a
Clarification: This is because the loss of available energy from such fluids would be low.