Question

Assertion :A sphere, a cube and thin circular plate of the same mass are made of the same material. If all of them are heated to the same high temperature the rate of cooling is maximum for the plate and minimum for the sphere. Reason: The rate of loss of heat by radiation is proportional to the surface area.

• A. Assertion is False and Reason is True
• B. Reason is False and assertion is True
• C. Both Assertion and Reason are True and reason correctly explains assertion
• D. Both Assertion and Reason are True but assertion does not correctly explain reason

Answer 1

The correct option is C Both Assertion and Reason are True and reason correctly explains assertion

Let the rate of cooling be $\frac{d\theta }{dt}$
$\frac{d\theta }{dt}$ $\propto$ $A$ where $A$ is the surface area.
For a given volume sphere has the least surface area and circular plate has the maximum surface area.
Hence, the rate of cooling will be fastest for the circular plate.