The temperature at which a black body of unit area loses its energy at the rate of $1$ joule/second is
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(c) $E = \sigma {T^4}$ ==>$5.6 \times {10^{ - 8}} \times {T^4} = 1$
==>$T = {\left[ {\frac{1}{{5.6 \times {{10}^{ - 8}}}}} \right]^{1/4}}$ $=65 K$
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