Which of the following statements are true? 1) Heat and work are completely interchangeable forms of energy 2) Heat and work are not completely interchangeable forms of energy 3) Work can be converted completely into heat 4) Heat can be converted completely into work

Which of the following statements are true? 1) Heat and work are completely interchangeable forms of energy 2) Heat and work are not completely interchangeable forms of energy 3) Work can be converted completely into heat 4) Heat can be converted completely into work Correct Answer 2 & 3

Explanation:

Path functions:

• Path functions are defined as the thermodynamical variables which depend on the way/path in which the thermodynamical system achieved the initial and final states.
• The differential of path functions is inexact.
• Heat, work and entropy generation are path functions.

Point functions:

• Point functions are defined as the thermodynamic variable which depends on end states only i.e. initial and final states. They do not depend upon the path followed.
• The differential of point functions is exact.
• Pressure, temperature, volume, entropy, enthalpy, energy etc are point functions.

High grade and low-grade energy :

Based on the thermodynamic concepts, an energy source can be called as high-grade or low-grade, depending on the ease with which it can be converted into other forms.

• Electrical energy (or work) is called high-grade energy, as it is very easy to convert almost all of it into other energy forms such as thermal energy (say by using an electrical heater).
• Whereas, it is not possible to convert thermal energy (or heat) completely into electrical energy (typical efficiencies of thermal power plants are around 30 percent), hence thermal energy is called a low-grade energy.