The quantity of heat radiated per unit time by a perfectly black body at 300 K is `81kJ//s`. What is the power radiated by a body of emissivity 0.8 and having the same area as that of the black at 500 K ?

Options

A. `250 kJ/s`
B. `400 kJ/s`
C. `500 kJ/s`
D. `625 kJ/s`

Answer

C

Explanation

`((dQ)/(dt))_(2)/(((dQ)/(dt))_(1))=(sigmaAeT_(2)^(4))/(sigmaAT_(1)^(4))`
`therefore((dQ)/dt)_(2)/(81)=(0.8xx5^(4))/(3^(4))`
`therefore((dQ)/(dt))_(2)=0.8xx5^(4)=500kJ//s`