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

According to the NCERT text, 'The specific heat capacity is the property of the substance which determines the change in the temperature of the substance (undergoing no phase change) when a given quantity of heat is absorbed (or given off) by it. It is defined as the amount of heat per unit mass absorbed or given off by the substance to change its temperature by one unit.' Mathematically, it is expressed as $s = \frac{1}{m} \frac{\Delta Q}{\Delta T}$.

The NCERT text states, 'The SI unit of molar specific heat capacity is J mol$^{-1}$ K$^{-1}$'. J kg$^{-1}$ K$^{-1}$ is the unit for specific heat capacity (per unit mass).

From the NCERT text: 'For a mole of a solid, the total energy is $U = 3 k_B T \times N_A = 3 RT$. Now, at constant pressure, $\Delta Q = \Delta U + P \Delta V \cong \Delta U$, since for a solid $\Delta V$ is negligible. Therefore, $C = \frac{\Delta Q}{\Delta T} = \frac{\Delta U}{\Delta T} = 3R$'. This value generally agrees with experimental values at ordinary temperatures.

The NCERT text states, 'The specific heat capacity is the property of the substance... It depends on the nature of the substance and its temperature.' It does not depend on the amount of substance.

The NCERT text explains: 'However, in connection with specific heat capacity of gases, additional conditions may be needed to define C. In this case, heat transfer can be achieved by keeping either pressure or volume constant. If the gas is held under constant pressure during the heat transfer, then it is called the molar specific heat capacity at constant pressure and is denoted by $C_p$. On the other hand, if the volume of the gas is held constant, it is denoted by $C_v$.'

Specific heat capacity is defined as the amount of heat per unit mass required to change its temperature by one unit. Therefore, 4186 J kg$^{-1}$ K$^{-1}$ means that 4186 Joules of heat energy are needed to raise the temperature of 1 kg of water by 1 Kelvin (or 1 degree Celsius).

From the NCERT text: 'The old unit of heat was calorie. One calorie was earlier defined to be the amount of heat required to raise the temperature of 1g of water by 1°C.' It further refines this to '1g of water from 14.5 °C to 15.5 °C' for a precise definition.

The NCERT text explicitly states: 'For an ideal gas, the molar specific heat capacities at constant pressure and volume satisfy the relation $C_p - C_v = R$' where R is the universal gas constant.

Given $\Delta Q = ms \Delta T$. If $\Delta Q$ and $m$ are constant for both substances, then $s \propto 1/\Delta T$. A smaller temperature change ($\Delta T$) implies a larger specific heat capacity ($s$). Therefore, $s_A > s_B$.

The NCERT text states: 'Since in SI units, we use the unit joule for heat, work or any other form of energy, the term mechanical equivalent is now superfluous and need not be used.' It was essentially a conversion factor between calories and joules.