Question

Imagine 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}⟶E=

λ

hc

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,

\begin{gathered} \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 \end{gathered}

E=

500×10

−9

6.626×10

−34

×3×10

8

E=

5

6.626×3

×10

−19

E≃3.975×10

−19

J

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

\begin{gathered} \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\end{gathered}

n=

3.975×10

−19

100

n≃0.25×10

21

n=2.5×10

20

photons/sec

Hope it Helps.