Question

The ratio of emissive power of a perfect black body at 927°C and 327°C is ______.

Options

• 2 : 1

• 4 : 1

• 8 : 1

• 16 : 1

Answer 1

The ratio of emissive power of a perfect black body at 927°C and 327°C is 16 : 1.

Explanation:

Convert the temperatures to Kelvin:

927°C = 927 + 273 = 1200K

327°C = 327 + 273 = 600K

Use Stefan-Boltzmann law which states that the emissive power of a black body is proportional to the fourth power of its absolute temperature:

E ∝ T⁴

Calculate the ratio of emissive powers:

`((E_1200K)/(E_600K))=(1200/600)^4`

= 2⁴ 

= 16