Physics : Heat And Thermodynamics

Q 4 / 11

UPSC CSE Prelims 2003

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?

EXPLANATION

Correct Option

Statement 3 is correct.

  • In an air-conditioner, the evaporator coils are positioned inside the room. These coils absorb heat from the room air, leading to its cooling.
  • The refrigerant, having absorbed this heat, then flows to the condenser coils, which are located outside the conditioned space.
  • At the condenser coils, the absorbed heat is released or rejected to the external environment, completing the refrigeration cycle.

Incorrect Options

Statement 1 is incorrect.

  • Steam at 100°C contains a greater amount of heat energy than boiling water at 100°C.
  • This additional energy is known as the latent heat of vaporization, which is absorbed during the phase transition from liquid water to steam at a constant temperature.
  • Consequently, steam at 100°C possesses a higher internal energy content compared to boiling water at the same temperature.

Statement 2 is incorrect.

  • The latent heat of fusion of ice is approximately 334 kJ/kg.
  • The latent heat of vaporization of water is approximately 2260 kJ/kg.
  • These values are not equal; the energy required for vaporization is significantly higher than that for fusion.

Options (a), (b), and (c) are incorrect as they include one or both of the factually inaccurate statements 1 and 2. Only statement 3 is correct.

SOURCENCERT Class 11 Physics Chapter 11: Thermal Properties of Matter, Chapter 12: Thermodynamics