What is the radiant energy absorbed per second by his head when it is covered with hair?

by pdxjmorris

Question by EmilyStone: What is the radiant energy absorbed per second by his head when it is covered with hair?
A person is standing outdoors in the shade where the temperature is 28 degrees C. What is the radiant energy absorbed per second by his head when it is covered with hair? The surface area of the hair (assumed to be flat), is 160 cm^2 and its emissivity is 0.85.

Best answer:

Answer by anilbakshi
Head temperature T = (37+273) = 310 K
heat radiates thermal energy owing to its surroundings (hair) at To (273+28) or 301 K
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Hair in turn keeps (15% – its absoptivity) of this energy and emits (85% – its emmisivity) to air.
emmisivity + absortivity = 1=0.85+ 0.15
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E-dot (emited)= watt = 0.85 * sigma * A * [T^4 - T0^4]
E-dot (absorbed) = 0.15 * sigma * A * [T^4 - T0^4]
= 0.15*(160*10^-4)* 5.67*10^-8 [310^4 - 301^4]
= 0.14 Joule/sec

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