Question

A black body with surface area 0.001 `m^(2)` is heated upto a temperature 400 K and is suspended in a room temperature 300K. The intitial rate of loss of heat from the body to room is
A. 10 W
B. 1W
C. 0.1W
D. 0.5 W

Answer 1

Correct Answer - B
b) The rate of heat emission, u = `sigmaAT^(4)`.
At room temperatures to the rate of absorption is
`u_(0)=sigmaAT_(0)^(4)`
The net rate of heat loss.
`u-u_(0)=sigmaA(T^(4)-T_(0)^(4))`
Given that A=0.001`m^(2)`
T=400K and `T_(0)`=300K
Thus, `u-u_(0)` = `5.67 xx 10^(-8) xx 0.001 xx [(400)^(4)-(300)^(4)]`=0.99 W