Question

The temperature of the filament of a lamp is 2100K and its surface area is 4 x ${10}^{-4}$.$m^2$ If the emissivitv of the filament is 0.453 then the power of the lamp is

• A. 100 watt
• B. 200 watt
• C. 400 watt
• D. 0 watt

Answer 1

The correct option is B 200 watt

Given,

$T=2100K$

$A=4\times {10}^{-4}{m}^2$

$e=0.453$

By use of stafan's law

$P=e\rho T^4\times A$

Here $\rho$ is stafan's constant value is $5.67\times {10}^{-8}W{m}^{-2}{K}^{-4}$

Put all the value in above equation

$P=e\rho T^4\times A$

$P=0.453\times 5.67\times {10}^{-8}\times {\left(2100\right)}^4\times 4\times {10}^{-4}=1998105.6\times {10}^{-4}=199.81\approx 200W$

correct option is B