Notes
Quantity of Heat — MCQs
Newton's law of cooling, water equivalent, latent heat and change of phase.
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1. Newton's law of cooling is valid when:
easyExplanation: The law holds only for small temperature differences between the body and its surroundings, when the rate of heat loss is proportional to the temperature difference. -
2. In the method of mixture, the heat capacity of the calorimeter is usually expressed as its:
easyExplanation: The water equivalent W = m_cal c_cal / c_w is the mass of water that absorbs the same heat as the calorimeter for the same temperature rise. -
3. While ice is melting at 0 °C, the heat supplied is used to:
easyExplanation: During a change of phase the temperature (and hence the average kinetic energy) stays constant; the latent heat increases the potential energy by working against intermolecular forces. -
4. The SI unit of specific latent heat is:
easyExplanation: Specific latent heat is heat per unit mass, L = Q/m, so its unit is J kg⁻¹. There is no temperature term because the temperature does not change. -
5. When steam condenses to water at 100 °C, it:
easyExplanation: Condensation is the reverse of vaporization, so the latent heat of vaporization is released. This is why a steam burn is more severe than a burn from water at 100 °C.