Thermal Properties of Matter MCQs for NEET — Physics Questions with Answers

The NCERT text states, 'For water, the latent heat of fusion and vaporisation are $L_f = 3.33 imes 10^5 ext{ J kg}^{-1}$ and $L_v = 22.6 imes 10^5 ext{ J kg}^{-1}$, respectively. ... $22.6 imes 10^5 ext{ J}$ of heat is needed to convert 1 kg water into steam at 100 °C.' This refers to the latent heat of vaporization.

The NCERT text mentions, 'During the sublimation process both the solid and vapour states of a substance coexist in thermal equilibrium.'

The NCERT text states, 'Its SI unit is J kg–1. The value of L also depends on the pressure. Its value is usually quoted at standard atmospheric pressure.' Also, $Q = mL$, so it depends on the mass. Thus, it depends on the mass of the substance and the characteristic of the substance, which implies inherent properties and conditions like pressure.

The NCERT reference clearly defines this relationship as '$Q = m L$ or $L = Q/m$ (10.13)', indicating that $Q = mL$ is the correct formula.

The NCERT text states, 'Note that when heat is added (or removed) during a change of state, the temperature remains constant.' A horizontal segment on a temperature-heat plot signifies that heat is being added without a change in temperature, which is characteristic of a phase transition.

The context states: 'Here $\alpha_V$ is also a characteristic of the substance but is not strictly a constant. It depends in general on temperature (Fig 10.6). It is seen that $\alpha_V$ becomes constant only at a high temperature.' Therefore, option 3 is incorrect.

The context states: 'If the substance is in the form of a long rod, then for small change in temperature, $\Delta T$, the fractional change in length, $\Delta l/l$, is directly proportional to $\Delta T$. where $\alpha_l$ is known as the coefficient of linear expansion (or linear expansivity)...'

The context explicitly states: 'The relation between them is : $\alpha_V = 3\alpha_l$'.

From Table 10.1, $\alpha_l$ for Glass (pyrex) is $0.32 \times 10^{-5} K^{-1}$ and for Copper is $1.7 \times 10^{-5} K^{-1}$. Comparing these, $1.7 / 0.32 \approx 5.3$, so copper expands about five times more than glass.

The context defines this phenomenon: 'What happens by preventing the thermal expansion of a rod by fixing its ends rigidly? Clearly, the rod acquires a compressive strain due to the external forces provided by the rigid support at the ends. The corresponding stress set up in the rod is called thermal stress.'