The temperature of a body is increased from `–73°C` to 327°C. Then the ratio of emissive power is –

Options

A. `27:1`
B. `81:1`
C. `1:27`
D. `1:81`

Answer

D

Explanation

According to Stefan.s law, the radiant energy emitted by a perfectly black body per unit area per second (i.e, emissive power or radiancy) is directly proportional to the fourth power of its absolute temperature. i.e. `E prop T^(4) or E= sigma T^(4)`
where `sigma` is Stefan.s constant whose value is `5.67 xx 10^(-8) W//m^(2) K^(4)`
As `TK = t^(@) C + 273`
`:. T_(1) = -73^(@)C + 273 = 200K, T_(2) = 327^(@)C + 273 = 600K`
`:. (E_(1))/(E_(2)) = ((T_(1))/(T_(2)))^(4) = ((200K)/(600K))^(2) = ((1)/(3))^(4) = (1)/(81)`