Question

The graph shows the variation of temperature T of one kilogram of a material with the heat H supplied to it. At point O, the substance is in the solid state. From the graph, which of the following statement is correct?

• A. $T_{2}$ is the melting point of the solid.
• B. $A B$ represents the change of state from solid to liquid. $\left( H _{2}+ H _{1}\right)$ represents the latent heat of fusion of the substance.
• C. $\left(H_{2}+H_{1}\right)$ represents the latent heat of fusion of the substance.
• D. $\left(H_{3}-H_{1}\right)$ represents the total latent heat of vaporisation of the liquid.

Answer 1

Answer: (B)

Since in the region $A B$, temperature is constant, therefore at this temperature, phase of the material changes from solid to liquid and $\left(H_{2}-H_{1}\right)$ heat will be absorbed by the material. This heat is known as the heat of melting of the solid. Similarly in the region $C D$, temperature is constant therefore at this temperature, phase of the material changes from liquid to gas and $\left( H _{4}- H _{3}\right)$ heat will be absorbed by the material. This heat as known as the heat of vaporisation of the liquid.
Thus, the statement given in option is correct, rest are incorrect.