Question

A copper ball of diameter d = 1.2 cm was placed in an evacuated vessel whose walls are kept at the absolute zero temperature. The initial temperature of the ball is T₀ = 300 K. Assuming the surface of the ball to be absolutely black, find how soon its temperature decreases η = 2.0 times.

Answer 1

In time dt after the instant t when the temperature of the ball is T, it loses

Joules of energy. As & result its temperature falls by - dT and