Question

At what rate, photons are emitted from the lamp?

• A. $3\times {10}^{20}photons{s}^{-1}$
• B. $2\times {10}^{20}photons{s}^{-1}$
• C. $5\times {10}^{20}photons{s}^{-1}$
• D. $1\times {10}^{20}photons{s}^{-1}$

Answer 1

The correct option is A $3\times {10}^{20}photons{s}^{-1}$

Power of the beam $P=100W$
Wavelength $\lambda =5890A^o=5890\times {10}^{-10}m$
Energy of photon $E=\frac{hc}{\lambda }$
Number of photons absorbed per second $N=\frac{P}{E}=\frac{P\lambda }{hc}$
$\therefore$ $N=\frac{100\times 5890\times {10}^{-10}}{6.62\times {10}^{-34}\times 3\times {10}^8}=3\times {10}^{20}$ photons per second