A matte-painted metal plate is assumed to behave like a grey body

PHYSICS · Subjective · CBSE · Physics · Thermal Properties of Matter · Thermal Properties of Matter

Problem

A matte-painted metal plate is assumed to behave like a grey body. Its radiant power per unit area RsR_{s} is measured at three different temperatures: TT (K): 700, 800, 900 RsR_{s} (kW\,m−2^{-2}): 12.0, 19.0, 28.0 (i) For each temperature, calculate the corresponding blackbody radiant power RbR_{b} using the accepted constant 5.67×10−8  W m−2 K−45.67\times10^{-8}\;\text{W\,m}^{-2}\,\text{K}^{-4}. (ii) Using the results of part (i), determine the emissivity ε=Rs/Rb\varepsilon=R_{s}/R_{b} of the surface at every temperature. (iii) Evaluate whether ε\varepsilon can be treated as temperature-independent for this surface, giving numerical justification. (iv) Suggest one physical reason why a matte surface might show a gradual change in emissivity with temperature.

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