Question

A tungsten filament lamp of power $625$ watt is at 2227${}^o$C. The emissivity of the filament is $0.16$. If $\sigma =$ $6\times 10$${}^{-8}$ Wm${}^{-2}$K${}^{-4}$, the surface area of the filament is nearly :

• A. $16m^2$
• B. $16.67\times 10$${}^{-4}{m}^2$
• C. $625\times 10$${}^{-4}{m}^2$
• D. $1667m^2$

Answer 1

Answer: (B)

$16.67\times 10$${}^{-4}{m}^2$

$E=\sigma \epsilon A{T}^4$

$A=\frac{E}{\epsilon \sigma T^4}=\frac{625}{0.16\times 6\times {10}^{-8}\times {2500}^4}=16.67\times {10}^{-4}{m}^2$