A black body at a temperature of `227^(@)C` radius head at a rate of `20 cal m^(-2)s^(-1)`. When its temperature is raised to `727^(@)C` the radiated by it in cal `m^(-2)s^(-1)` will be closet

Options

A. `40`
B. `160`
C. `320`
D. `640`

Answer

c

Explanation

From stefarfs law the rate at which an object radiance energy € per unit is propertional is the fourth power of abscilute tempetature of the body (T)
` P = sigma T^(4)`
where `sigma` is stefarfs 's constant
Given `P_(1) = 20 cal m^(-2)s^(-1)`
`:. T_(1) = 227+ 273 = 300 K`
`:. 2theta = sigma (500)^(4)`...(1)
Also `T_(1) = 722^(@)C = 727 + 273 = 1000K`
`:. P_(2) = sigma (1000)^(4)` ...(2)
`:. (20)/(P_(2)) = ((500)^(4))/((1000)^(4))`
`P_(2) = ((1000)^(4) xx 20)/(500)^(4) = 320 cal m^(-2)s^(-1)`