A square metal plate of area is maintained at a uniform temperature of

PHYSICS · Subjective · A Level · Physics · Further mechanics and thermal physics · Further mechanics and thermal physics

Problem

A square metal plate of area

0.20\,\text{m}^2

is maintained at a uniform temperature of

800\,\text{K}

. The Stefan constant may be taken as

5.67\times10^{-8}\,\text{W m}^{-2}\text{K}^{-4}

. (i) If the surface emissivity is

0.70

, calculate the radiant power emitted by the plate when it faces outer space assumed at

0\,\text{K}

. (ii) The plate is now polished so that its emissivity becomes

0.40

. Determine the percentage reduction in the radiant power emitted compared with part (i). (iii) Returning to the original emissivity of

0.70

, find the net radiant power lost by the plate if it is placed inside a large room whose walls are at

300\,\text{K}

. Ignore any mode of heat transfer other than radiation.