Question

Heat is supplied to a solid material at a constant rate. The variation of temperature of the material with heat input is as shown in the figure.The slope of DE represents:

• A. Latent heat of liquid
• B. Latent heat of vaporization
• C. Heat capacity of vapour
• D. Inverse of heat capacity of vapour

Answer 1

The correct option is D Inverse of heat capacity of vapour

In the given graph, $AB$ and $CD$ represent the phase changes in solid material. At $AB$, the solid material converts into liquid and at $CD$, it converts into vapour.
i.e in part $DE$, the material is in vapour state.

Let us assume $c$ to be heat capacity of vapour.
We know from the definition of heat capacity that,
$dQ=cdT$
$\therefore \frac{dT}{dQ}=\frac{1}{c}$ = Slope of $T-Q$ graph.
where $Q$ is the heat input and $T$ is the temperature.

Hence, we can conclude that the slope of $T-Q$ graph at $DE$ represents the inverse of the heat capacity of vapour.
Thus, option (d) is the correct answer.