Question

Availability is:

• A. Work lost due to friction
• B. Maximum useful work
• C. Heat available from system
• D. Energy in environment

Hint:

Availability = maximum useful work obtainable as a system reaches equilibrium with the surroundings. It quantifies usable energy.

Answer 1

The Correct Option is B

Availability (also called exergy) is defined as the maximum useful work that can be obtained from a system as it comes to equilibrium with a reference environment.
It is a measure of the useful energy in a system that can be converted into work.
Key points:
- Availability represents the potential to do work.
- It decreases in real processes due to irreversibilities like friction, mixing, heat transfer through a finite temperature difference, etc.
- It is not the same as the total energy — only the usable part.
Incorrect options:
- (1) Work lost due to friction is irreversibility, not availability.
- (3) Heat alone does not define work potential.
- (4) Energy in the environment isn't what's meant by system availability.