A pinhole is made in a hollow sphere of radius `5cm` whose inner wall is at temperature `727^(@)C`. Find the power radiated per unit area.
[Stefan's constant `sigma=5.7xx10^(-8)J//m^(2)sK^(4)`, emissivity `(e)=0.2`]

Explanation

Given:
Temperature of inner wall
`=727^(@)C=727+273K`
`=1000K`
Stefan's constant `sigma=5.7xx10^(-80J//m^(2)K^(4)`
Emissivity,`e=0.2`
By the Stefan's law, power radiated per unit area for not a perfectly black body is given by,
`(Q)/(AT)=e sigma T^(4)`
`=0.2xx5.7xx10^(-8)xx(1000)^(4)`
`=11.4xx10^(3)`
`=1.14xx10^(4)watt/m^(2)`