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 `20W`
D. The power emitted by `B` is `180W`

Answer

A

Explanation

For body `A` emissivity =absorptivity `= 0.2`
So from Kirchhoft,s law `(E)/(a)|._("black body")=(E)/(a)|_(B)`
`rArr (100)/(1) = (E)/(0.2) rArr E = 20W//m^(2)`
Emitted power by `B` is `p = EA = 200W` .