UPSC Prelims PYQ 2003: Which thermodynamics statements about steam, latent heat, and...

Consider the following statements:

1. Steam at 100° C and boiling water at 100° C contain same amount of heat.
2. Latent heat of fusion of ice is equal to the latent heat of vaporization of water.
3. In an air‑conditioner, heat is extracted from the room air at the evaporator coils and is rejected out at the condenser coils.

Which of these statements is/are correct?

1. 1 and 2
2. 2 and 3
3. Only 2
4. Only 3

Explanation

Option (d) is correct

• Statement 1 is incorrect because steam at 100°C contains more heat than boiling water at 100°C due to the presence of the latent heat of vaporisation. Statement 2 is incorrect because the latent heat of vaporisation of water is much greater than the latent heat of fusion of ice. Statement 3 is correct because an air conditioner absorbs heat from the room air through the evaporator coils and releases it outside through the condenser coils.

Answer: (d) Only 3