The temperature of a radiating surface changes from 400 K to 1200 K. The ratio of total emissive powers at the higher and lower temperatures would be-

Question

Question

This question was previously asked in

NPCIL SA/ST ME GJ Held on 08/11/2019, Shift-1

Answer 1

Concept:

Stefan-Boltzmann Law

The thermal energy radiated by a black body per second per unit area is proportional to the fourth power of the absolute temperature and is given by:

E ∝ T4

E = σT4

σ = The Stefan – Boltzmann constant = 5.67 × 10-8 W m-2K-4

Calculation:

Given:

T₁ = 400 K, T₂ = 1200 K

\(\frac{{{E_2}}}{{{E_1}}} = {\left( {\frac{{{T_2}}}{{{T_1}}}} \right)^4} = {\left( {\frac{{1200}}{{400}}} \right)^4} =3^4 = 81\)