Question

A spherical body of area $A$ and emissivity $e=0.6$ is kept inside a perfectly black body. Total heat radiated by the body at temperature T is :

• A. $0.4eA{T}^4$
• B. $0.8eA{T}^4$
• C. $0.6eA{T}^4$
• D. $1.0eA{T}^4$

Answer 1

The correct option is D $1.0eA{T}^4$

When a non black body is placed inside a hollow enclosure, the total radiation from the body is the sum of what it would emit in the open ( with $ϵ<1$ ) and the part of the incident radiation from the walls reflected by it. The two add up to a black body radiation.

Hence the total radiation emitted by the body is $1.0ϵA{T}^4$.