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. 1235J
• B. 2215J
• C. 2115J
• D. 2325J

Answer 1

The correct option is D 2325J

T=2000K, A=5 x ${10}^{-5}{m}^2,\epsilon =0.85\sigma =5.7\times {10}^{-8}$ MKS unit.
Energy radiated/sec = $A\epsilon \sigma T^4$
=$5\times {10}^{-5}\times 0.85\times 5.7\times {10}^{-8}x(2000{)}^4$
=$5\times 0.85\times 537\times {10}^{-13}\times {10}^{12}\times 16$
$=387.6\times {10}^{-1}$
Energy radiated/minute =$38.76\times 60$
= 2325.6J