Question

A blue lamp mainly emits light of wavelength $4500\, \mathring{A}$The lamp is rated at $150 \,W$ and $8\%$ of the energy is emitted as visible light. The number of photons emitted by the lamp per second is

• A. $3\times10^{19}$
• B. $3\times10^{24}$
• C. $3\times10^{20}$
• D. $3\times10^{18}$

Answer 1

Answer: (A)

Number of photons emitted per second
$\frac{8\% of P}{E}=\frac{8P\lambda}{100 hc}=\frac{8\times150\times4500\times10^{-10}}{100\times6.63\times10^{-34}\times3\times10^{8}}$
$=3\times10^{19}$ photons per second