A spherical tungsten pices of radius `1.0cm` is suspended in an evacuated chamber maintained at `300K. The pices is maintained at 1000K by heating it electrically. Find the rate at which the electrical energy must be supplied. The emissivity of tungsten is `0.30` and the Stefan constant sigma is `6.0xx10^(-s)Wm^(-2)K^(-4)` .

A spherical tungsten pices of radius `1.0cm` is suspended in an evacua

1.	A spherical tungsten pices of radius `1.0cm` is suspended in an evacuated chamber maintained at `300K. The pices is maintained at 1000K by heating it electrically. Find the rate at which the electrical energy must be supplied. The emissivity of tungsten is `0.30` and the Stefan constant sigma is `6.0xx10^(-s)Wm^(-2)K^(-4)` .
Answer» Correct Answer - B `r=1cm =1xx10^(-2)m,` `A =4 pi (10^(-2))^(2)` `=4 pi xx10^(-4)m^(2)` `e=0.3, sigma =6xx10^(-8)` `(E/t)e sigma A (T_(2)^(4)-T_(1)^(4))` `=0.3xx6xx10^(-8)xx4 pixx10^(-4)` `xx[(1000)^4-(300)^4]` `=0.3xx6xx4 pi xx10^(-12)` `xx[1-0.0081]xx1012` `=0.3xx64xx3.14xx9919xx10^(-5)` `=22.4=22W`.

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