A body which has a surface area`5.00 cm^(2)` and a temperature of `727^(@)C` radiated 300 j of energy each minute. What is the emissivity of body? Steafan's constant `=5.67xx10^(-8) Wm^(-2) K^(-4)`.

Answer

`[0.18]`

Explanation

Here, `A=5.00 cm^(2) =5.00xx10^(-4) m^(-2)`,
`T=727+273=1000 K`,
Energy radiated per second, `P=(300 j)/(60 s) =5 js^(-1)`
Ac counting to stefan's law, the energy radiatiated per second by the body is `P=EA= epsilon sigma T^(4)A`
Emissivity `epsilon=(P)/(sigma T^(4) A)`
`=(5)/((5.67xx10^(-8))xx(1000)^(4)xx(5xx10^(-4)))= 0.18`