JEE PHYSICS MCQ: THERMAL PROPERTIES OF MATTER

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A copper sphere is suspended in an evacuated chamber maintained at

300 \mathrm{~K}

. The sphere is maintained at a constant temperature of

500 \mathrm{~K}

by heating it electrically. A total of

300 \mathrm{~W}

of electric power is needed to do it. When half of the surface of the copper sphere is completely blackened

600 \mathrm{~W}

is needed to maintain the same temperature of the sphere. Calculate the emissivity of copper.

View answer and explanation

Correct option: A

\mathrm{e}=\frac{1}{3}

Option A (

\mathrm{e}=\frac{1}{3}

) is correct because it is calculated by setting up a ratio of the power needed in both cases using Stefan-Boltzmann law.

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