A laser pointer consumes 15 mW of electrical power and is 20 % efficient in converting this power into a monochromatic light beam. If the energy of a single photon in this beam is 3.0 10⁻¹⁹ J , what is the number of photons emitted by the laser per second?

Step-by-step solution

Electrical power consumed, P_ in = 15 mW = 15 10⁻³ W Efficiency, = 20 % = 0.20 Power of the emitted light beam, P_ out = P_ in = 0.20 15 10⁻³ W = 3 10⁻³ W Energy of a single photon, E = 3.0 10⁻¹⁹ J Number of photons emitted per second, n = P_ out E n = 3 10⁻³ 3.0 10⁻¹⁹ = 1.0 10¹⁶ Answer: 1.0 10¹⁶