Question

A source of laser is emitting a laser beam of wavelength 6328 A° with an average power of 4.5 mW. Find the number of photons emitted per second by the laser. *​

Answer 1

Given,

A source of laser is emitting a laser beam of wavelength 6328 A° with an average power of 4.5 mW.

To find,

The number of photons emitted per second by the laser.

we know, energy of each photon is given by E = hc/λ

let n is the number of photons.

so, energy of n photons = nE = nhc/λ

power = energy/time

⇒Power = nhc/λt

⇒power = (n/t) hc/λ

⇒power = number of photons per second × hc/λ

⇒4.5 mW = number of photons per second × (6.63 × 10¯³⁴ × 3 × 10^8)/(6328 × 10^-10)

⇒number of photons per second = 4.5 × 10¯³/(3.143 × 10^-19)

⇒number of photons per second = 1.43 × 10^16