Structure of Atom Part 1

Power of the source =1‌mW=10−3W
Energy of one photon, E=hv=

hc

λ

where, h=6.6×10−34‌Js
c=3×108m∕s and
λ = 1000 nm
=1000×10−9m (1‌nm=10−9m)
=10−6m
E=

6.6×10−34×3×108

10−6

≅20×10−20J
Power = number of photons emitted in one second × energy of 1 photon.
10−3=n×20×10−20
⇒n=

10−3

20×10−20

=0.5×1016
Number of photons emitted in 1s=0.5×1016
Number of photons emitted in 0.1s=0.5×1016×0.1=50×1013
x×1013=50×1013
x = 50