Question

Calculate the energy radiated per minute from the filament of an incandescent lamp at $2000\, K$. If the surface area is $5 \times 10^{-5} m ^{2}$ and its relative emittance is $0.85, \sigma=5.7 \times 10^{-8}$ MKS units

• A. 1230 J
• B. 2325 J
• C. 2115 J
• D. 2315 J

Answer 1

Answer: (B)

From Stefan's law of radiation, the energy radiated $(E)$ is given by
$E=e \sigma T^{4} A t$
Given, $e=0.85,\, \sigma=5.7 \times 10^{-8}$,
$T=2000\, K ,$
$A=5 \times 10^{-5} m ^{2},\, t=60\, s$
$E=0.85 \times 5.7 \times 10^{-8} \times(2000)^{4} \times 5 \times 10^{-5} \times 60$
$E=2325\, J$