Question

A sphere, a cube and a thin circular plate have the same mass and are made of the same material. All of them are heated to the same temperature. The rate of cooling is

• A. the maximum for the sphere and minimum for the plate
• B. the maximum for the sphere and minimum for the cube
• C. the maximum for the plate and minimum for the sphere
• D. the same for all the three.

Answer 1

The correct option is C

the maximum for the plate and minimum for the sphere

Since the sphere, the cube and the circular plate are made up of the same material, their density will be the same and hence the volume. For the same volume, the surface area of the plate is the largest and that of the sphere is the smallest. The rate of loss of heat by radiation is proportional to the surface area. Hence, the plate will cool the fastest while the sphere the slowest and the correct choice is (c).