Question

Imagine a source emitting 100W of green light at a wavelength of 500nm .How many photons per second are emerging from the source?​

Answer 1

Answer:

2.5 × 10²⁰ photons per second

Explanation:

Given :

A source is emitting 100W of green light at a wavelength of 500 nm

To find :

the number of photons emerging from the source per second

Solution :

Energy of a photon is given by,

$\longrightarrow \tt E = \dfrac{hc}{\lambda}$

where

h denotes the Plank's constant (6.626 × 10⁻³⁴ J-s)

c denotes the speed of the light

λ denotes the wavelength of the photon

Substituting the values,

$\sf E = \dfrac{6.626 \times 10^{-34} \times 3 \times 10^8}{500 \times 10^{-9}} \\ \sf E = \dfrac{6.626 \times 3}{5} \times 10^{-19} \\ \sf E \simeq 3.975 \times 10^{-19} J$

The number of photons emerging per second = Power of the source/Energy of a photon

$\sf n = \dfrac{100}{3.975 \times 10^{-19}} \\\sf n \simeq 0.25 \times 10^{21} \\ \sf n = 2.5 \times 10^{20} \ photons/sec$