Question

A circular metallic disc of radius $R$ has a small circular cavity of radius $r$ as shown in the figure. On heating the disc

• A. $R$ increases and $r$ decreases
• B. $R$ decreases and $r$ increases
• C. Both $R$ and $r$ increases
• D. Both $R$ and $r$ decreases

Answer 1

The correct option is C Both $R$ and $r$ increases

For any material the areal expansion may be expressed in terms of the linear expansion coefficient $\alpha$.

In a thermal expansion of an object, superficial expansion always occur in radially outward direction.

So, the area of circular cavity increases when the disc expands on heating. Thus, we can say that both $R$ and $r$ increases.




Hence, option (c) is the correct answer.

Caution:- Always remember that cavity will also expand, since the material at the periphery of the cavity tends to expand radially outwards.