Question

Calculate the number of photons emitted in 10 hour by a 60 W sodium lamp.[ ${\lambda }_{p}hoton$ = 5893 $\lambda$]

Answer 1

Given,

Power$=60W,Time=10h=10\times 3600=3.6\times {10}^{4}sec$

$Energy=Power\times Time$

$=60\times 3.6\times {10}^4=21.6\times {10}^{5}J$

Energy of one photon$=\frac{hc}{\lambda }$ Given $\lambda =5.893\times {10}^{-7}m$

$=\frac{6.63\times {10}^{-34}\times 3\times {10}^8}{5.893\times {10}^{-7}}$

$=\frac{19.89\times {10}^{-19}}{5.893}J$

$\therefore$ Number of photons$=\frac{Energy}{Energyofonephoton}$

$=\frac{2.16\times {10}^6\times 5.893}{19.89\times {10}^{-19}}$

$=0.64\times {10}^{25}$