Heat and Mass Transfer
Depending on the radiating properties, a body will be black when (Where a = absorptivity, p = reflectivity, X = transmissivity.)

X = 0, a + p = 0
P = 0, x = 0 and a = 1
P= 1, T = 0 and a = 0
P = 0, x = 1 and a = 0

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Heat and Mass Transfer
According to Prevost theory of heat exchange

It is impossible to transfer heat from low temperature source to t high temperature source
Heat transfer in most of the cases takes place by combination of conduction, convection and radiation
All bodies above absolute zero emit radiation
Heat transfer by radiation requires no medium

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