Question

What is the unit of latent heat of the body?
$\begin{align}
  & \text{A}\text{. }\dfrac{\text{Joule}}{\text{kg}} \\
 & \text{B}\text{. }\dfrac{\text{Calorie}}{\text{ }\!\!{}^\circ\!\!\text{ C}} \\
 & \text{C}\text{. }\dfrac{\text{Joules}}{\text{ }\!\!{}^\circ\!\!\text{ C}} \\
 & \text{D}\text{. }\dfrac{\text{kg}}{\text{Joules}} \\
\end{align}$

Answer 1

Hint: When change of states happen (i.e. when a solid changes to liquid or liquid changes to gas), the substance absorbs heat but does not change or increase its temperature. This heat used to change the state is hidden or latent (lies hidden). Latent heat is defined as the amount of heat required to change the state of unit mass of a substance at a constant temperature and pressure.

Formula used:
$Q=mL$ where, $Q=\text{ Heat required}$, $m=\text{mass of substance}$, $L=\ \text{Latent heat}$

Complete step-by-step answer:
Consider a substance of mass m undergoes a change in state at constant temperature. The amount of heat required for this process is $Q=mL$ where, $Q=\text{ Heat required}$, $ L=\ \text{Latent heat}$, $m=\text{mass of substance}$.
So, $L=\dfrac{Q}{m}$
The S.I unit of $Q$ is Joule and of mass is $kg$
So the unit of latent heat is $\dfrac{Joule}{kg}\text{ or }Joule\times k{{g}^{-1}}$

So, the correct answer is “Option A”.

Additional Information: Latent heat of fusion: The amount of heat required to change the state of unit mass of a substance from solid state to liquid state at melting point is called latent heat of fusion or latent heat of melting. It is usually denoted by ${{L}_{f}}$.
Latent heat of evaporation: The amount of heat required to change the state of unit mass of a substance from liquid state to vapour at boiling point is called latent heat of evaporation or latent heat of boiling. It is usually denoted by ${{L}_{v}}$.

Note: Don’t get confused between Latent heat and specific heat. Latent heat is defined as the amount of heat required to change the state of a substance at constant temperature whereas specific heat is defined as the amount of heat required to increase the temperature of a substance by one degree. So
$c=\dfrac{\Delta Q}{M\times \Delta T}$
Where $c=\text{specific heat of substance}$
$\Delta Q=\text{Heat required to change the temperature by }\Delta T$
$M=\text{mass of the substance}$
S.I units of specific heat is $Joule\times k{{g}^{-1}}\times Kelvi{{n}^{-1}}$