Question

Energy is emitted from a hole in an electric furnace at the rate of 20 W, when the temperature of the furnace is 727 ºC. What is the area of the hole? (Take Stefan’s constant σ to be 5.7 ×10^-8 J s^-1 m^-2 K^-4)

Answer 1

Given: Q/t = 20W, T=273+727=1000 K, σ = 5.7×10^-8 Js^-1/m².K^-4

Q/t = σAT⁴

∴ The area of the hole,

A = (Q/t)/(σT⁴ ) = 20(5.7×10^-8 ×1000⁴ )  = 20×10^-4/5.7 m²

= 3.509×10^-4 m²