1.

How many watts of energy is required to keep a black body in the form of a cube of side 1 cm at 2000 K ? (Temperature of surrounding is 27^(@)C and sigma=5.67xx10^(-8)"W m"^(-2)K^(-4) ) :

Answer»

444 W
544 W
844 W
None of the above

SOLUTION :Area `A=6l^(2)=6cm^(2)=6xx10^(-4)m^(2)`.
`E=sigma(T^(4)-T_(0)^(4))A=5*67xx10^(-8)[(2000)^(4)-(300)^(4)]xx6xx10^(-4)`.
`E=544` warr.
THUS correct choice is (B).


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