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Home  >>  JEEMAIN and AIPMT  >>  Physics  >>  Class11  >>  Thermodynamics
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A blackbody of surface area $\;100 cm^{2}\;$ is placed inside an enclosure . The enclosure has a constant temperature at $\;127^{0}C\;$ & the blackbody is maintained at $\;227^{0}C\;$ by heating it electrically . If $\;\sigma=6 \times 10^{-8} Wm^{-2}K^{-4}\;$ , electric power needed to maintain the temperature

$(a)\;12W\qquad(b)\;22W\qquad(c)\;32 W\qquad(d)\;24 W$

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Answer : 22 W
Explanation :
Area , $\;A = 10^{-2} m^{2}$
$T_{1}=227^{0}C=500 K$
Radiation emitted at $\;A \sigma T_{1}^{4}\;$
Radiation absorbed at $\;A \sigma T_{2}^{4}$
Therefore , The power needed = $\; A \sigma(T_{1}^{4}-T_{2}^{4})$
$=10^{-2}\times 6 \times 10^{-8} ((500)^{4}-(400)^{4})W$
$=2.214 \times 10^{11-10}W$
$=22.14 W$
answered Mar 13, 2014 by yamini.v

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