# Thermodynamics Questions and Answers – Efficiencies in Steam Power Plant

This set of Thermodynamics Multiple Choice Questions & Answers (MCQs) focuses on “Efficiencies in Steam Power Plant “.

1. The maximum work output that can be obtained per unit mass of steam is
a) reversible and isobaric enthalpy drop in turbine
b) reversible and isochoric enthalpy drop in turbine
c) reversible and adiabatic enthalpy drop in turbine
d) all of the mentioned

Explanation: The maximum work can be obtained from a reversible and adiabatic enthalpy drop in turbine but no real process is reversible.

2. The work done in irreversible adiabatic expansion by the turbine is called
a) external work
b) internal work
c) zero work
d) useful work

Explanation: This is because only the irreversibilities within flow passages of turbine are affecting steam state at turbine exhaust.

3. The internal efficiency is given by
a) internal output / ideal output
b) ideal output / internal output
c) internal output / heat supplied
d) none of the mentioned

Explanation: Here internal output is the ideal output minus the friction losses and other losses within the turbine.

4. The generator efficiency is given by brake output / output at generator terminals.
a) true
b) false

Explanation: The generator ( alternator ) efficiency is given by output at generator terminals / brake output of turbine.

5. The brake efficiency is given by
a) brake output / internal output
b) internal output / brake output
c) brake output / heat supplied
d) brake output / ideal output

Explanation: The brake output is also called shaft output and is given by internal output minus external losses.

6. The mechanical efficiency is given by
a) brake output / ideal output
b) brake output / internal output
c) brake output / heat supplied
d) internal output / brake output

Explanation: The brake output (shaft output) and is given by internal output minus external losses.

7. The brake efficiency is given by
a) mechanical efficiency / internal efficiency
b) internal efficiency / mechanical efficiency
c) internal efficiency * mechanical efficiency
d) none of the mentioned

Explanation: This comes from the relations of internal efficiency and mechanical efficiency.

8. Which of the following efficiency is true?
a) internal efficiency takes internal losses into consideration
b) mechanical efficiency only considers the external losses
c) brake efficiency considers both internal and external losses
d) all of the mentioned

Explanation: This the differences in internal, mechanical and brake efficiency.

9. The efficiency of boiler is given by
a) energy supplied / energy utilized
b) energy utilized / energy supplied
c) heat supplied / energy utilized
d) none of the mentioned

Explanation: The efficiency of boiler is the energy utilized / energy supplied.

10. Compressing steam in vapour form requires less work than compressing it in liquid form for same pressure rise.
a) true
b) false