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  4. Two circular discs A and B with equal radii are blackened. They are heated to same temperature and are cooled under identical conditions. What inference do you draw from their cooling curves?

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Q. Two circular discs $A$ and $B$ with equal radii are blackened. They are heated to same temperature and are cooled under identical conditions. What inference do you draw from their cooling curves?Physics Question Image

Bihar CECEBihar CECE 2008Thermal Properties of Matter

Solution:

According to Newton's law of cooling, rate of cooling is given by
$\left(\frac{-d T}{d t}\right)=\frac{e A \sigma}{m c}\left(T^{4}-T_{0}^{4}\right)$
where $c$ is specific heat of material.
or $\left(\frac{-d T}{d t}\right) \propto \frac{1}{c}$
ie, rate of cooling varies inversely as specific heat. From the graph, for $A$ rate of cooling is larger. Therefore, specific heat of $A$ is smaller.