Question

How many photons are emitted by a laser source
of 5 x 10-3 W operating at 632.2 nm in 2 s?
(h = 6.63 * 10-34 Js)
(1) 3.2 x 1016
(2) 1.6 x 1016
(3) 4 x 1016
(4) 0.4 x 1016​

Answer 1

Q) How many photons are emitted per second by a 5 mw laser operating at 620 nm?

given ,

wavelength = 620 nm

power = 5 mili watt

we know,

Energy of one photon = hc/lemda

where , h is plank' constant

c is velocity of light and lemda is wavelength .

after putting value of h and c

Energy of one photon = 12375/lemda( in A° )

Energy of one photon = 12375/( 6200 A°)

= 1.9959 ev

Energy of one photon = 1.9959 × 1.6× 10^-19 joule = 3.19 × 10^-19 Joule

now Let no of photon = n in one second

so, no of photon in one second = Power × one second/energy of one photon

= 5 × 10^-3/3.19 × 10^-19

= 1.56 × 10^(-3 +19 )

= 1.56 × 10^16

hence, no of photon per second = 1.56 × 10^16

u can refer this,,,,,,,,,,,,,,,,,,,,,,,buddy