# Thermodynamics Questions and Answers – Available Energy Referred to a Cycle

This set of Thermodynamics Multiple Choice Questions & Answers (MCQs) focuses on “Available Energy Referred to a Cycle”.

1. Which of the following is a type of energy?
c) both of the mentioned
d) none of the mentioned

Explanation: These are two types in which the sources of energy can be divided into.

2. Which of the following is an example of high grade energy?
a) mechanical work
b) electrical energy
c) water power and wind power
d) all of the mentioned

Explanation: These are some examples of the high grade energy.

3. The complete conversion of heat into shaft-work is impossible.
a) true
b) false

Explanation: This statement can be proved by the second law of thermodynamics.

4. Which of the following is an example of low grade energy?
a) heat or thermal energy
b) heat from nuclear fission or fusion
c) heat from combustion of fossil fuel
d) all of the mentioned

Explanation: These are few examples of low grade energy.

5. The part of ____ available for conversion is referred to ____
a) high grade energy, available energy
b) low grade energy, available energy
c) low grade energy, unavailable energy
d) high grade energy, unavailable energy

Explanation: Only some part of low grade energy is available for conversion.

6. The ____ obtainable from a certain heat input in a cyclic heat engine is called ____
a) minimum work output, available energy
b) maximum work output, available energy
c) minimum work input, unavailable energy
d) none of the mentioned

Explanation: Q1=AE+UE and the minimum energy that has to be rejected is called the unavailable energy.

7. The unavailable energy is the product of the lowest temperature of heat rejection and the change of entropy of system during the process of supplying heat.
a) true
b) false

Explanation: U.E.=T0*(change in entropy).

8. The lowest practicable temperature of heat rejected is the
a) given temperature
b) 0K
c) temperature of surroundings
d) 273K

Explanation: Work done and hence efficiency will be maximum when heat is rejected at the temperature of surroundings.

9. The available energy is known as ____ and the unavailable energy is known as ____
a) anergy, exergy
b) exergy, anergy
c) both are called exergy
d) both are called anergy

Explanation: Rant was the one who coined these terms.

10. Whenever heat is transferred through a finite temperature difference, there is always a decrease in the availability of energy so transferred.
a) true
b) false

Explanation: This is because of exergy lost due to irreversible heat transfer.

11. Exergy is lost due to
a) irreversible heat transfer
b) through finite temperature difference
c) during the process of heat addition
d) all of the mentioned

Explanation: The decrease in exergy is given by the product of lowest feasible temperature of heat rejection and the additional entropy change in the system.

12. Energy is said to be degraded each time it flows through a finite temperature difference.
a) true
b) false

Explanation: The exergy is mainly lost due to irreversible heat transfer through a finite temperature difference.

13. When considering a finite energy source, its working fluid expands,
a) reversibly
d) none of the mentioned

Explanation: For a finite energy source, expansion of working fluid is reversibly and adiabatically.

Sanfoundry Global Education & Learning Series – Thermodynamics.
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