1.

Two spheres of same material have radius 1 m and 4 m and temperature 4000 K and 2000 K respectively. The energy radiated per second by the first sphere isA. greater than that by the secondB. less than that by the secondC. equal in both casesD. the information is incomplete to draw any conclusion

Answer» Correct Answer - C
The energy radiated per second E, by a body of surface area A, at temperature T K, is given by
`E = esigma AT^(4)`
Hence, `E_(1) = esigma4pi(1)^(2) xx (4000)^(4) = esigmapi xx 1024 xx 10^(12) J s^(-1)`
and `E_(2) = esigma4pi(4)^(2)(2000)^(4) = esigmapi xx 1024 xx 10^(12) J s^(-1)`
So, `E_(1) = E_(2)`


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