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Bức xạ nhiệt (radiation)

Bức xạ nhiệt (radiation)

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Example:  How much does the human body

radiate?

----------------------------------------------------------------------Body temperature = 37 C = 37 +273 = 310 K,

Estimate surface area A = 1.5 m2        e = 0.70

H = e σ A T4

        = (0.70)(5.67 x 10-8)(1.5 m2 )(310)4

        = 550 watts (5 light bulbs)

----------------------------------------------------------------------The sun provides about 1000 watts per square

meter at the Earth's surface.  30 % is reflected by

human skin.  700 watts is absorbed per square

meter.  



sun & solar radiation

Temperature of surface (effective) 6000K

3.846×1026 W

energy is produced by nucle fusion, that converts

hydrogen into helium



Solar cooker



Pipes in Solar Panels are Painted Black



Hấp thụ và tỏa nhiệt bằng bức xạ

• Absorption and Emission of  Radiation

 



• Energy out = Energy in

 Emitted energy/Incident energy = Emissivity = e.  



Black Bodies







Black Bodies  

Summer clothing:  white

reflects

 radiant energy better than

black.







 Until equilibrium is reached,

white

 stripes on roads are at a lower

 temperature than unpainted

asphalt.

 Wrap an ice-cube in black cloth

 and another in aluminum foil

and

 place both in the sunshine.

 What

 will happen?



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