The emissive power of a black body at `T=300K` is `100Watt//m^(2)` consider a body B of area `A=10m^(2)` coefficient of reflectivity `r=0.3` and coefficient of transmission `t=0.5` its temperature is 300 K. then which of the followin is correct:

Options

A. The emissive power of `B` is `20W//m^(2)`
B. The emissive power of `B` is `200W//m^(2)`
C. The power emitted by `B` is `200"Watt"`
D. The emissivity of `B` is =` 0.2`

Answer

B

Explanation

For body `AP = sigmaAT^(4)`
`(P)/(A) = 100 = sigma xx 300^(4)`
For body `B`
`(P)/(A) = (sigmaT^(4)) in = (1-0.5-0.3) xx [sigmaxx300^(4)]`
` = 0.2 xx 100 = 20W//m^(2)`