A surface at temperature `T_(0)K` receives power `P` by radiation from a small sphere at temperature `T ltT_(0)` and at a distance d. If both `T` and d are doubled the power received by the surface will become .

Options

A. `8P`
B. `4P`
C. `2P`
D. `P`

Answer

B

Explanation

`(Power)/(Area)` = Intensity
Power absorbed by the foil = Intensity at foil xx Area of foil
`implies P = (P_(a))/(4pid^(2)) xx A = ((sigmaA_(theta) T^(4))/(4pid^(2)))A`
Now `P'= (sigmaA_(theta)(2T)^(4) xx A)/(4pi(2d)^(2)) = 4P`