Question

The average number of photons emitted per second by a laser of power \(6.6\times10^{-3}\ \text{W}\) producing a light of wavelength \(600\ \text{nm}\) is
\[ \text{(Planck's constant, } h=6.6\times10^{-34}\ \text{J s)} \]

• A. \(2\times10^{16}\)
• B. \(3\times10^{16}\)
• C. \(4\times10^{16}\)
• D. \(6\times10^{16}\)

Hint:

For photon emission problems, first calculate the energy of a single photon using \[ E=\frac{hc}{\lambda}. \] Then use \[ P=NE \] to determine the number of photons emitted per second.

Answer 1

The Correct Option is A

Step 1: Find energy of one photon.
\[ E_{photon} = \frac{hc}{\lambda} = \frac{6.6\times10^{-34}\times3\times10^8}{600\times10^{-9}} = 3.3\times10^{-19}\,\text{J} \]

Step 2: Divide power by photon energy.
\[ N = \frac{P}{E_{photon}} = \frac{6.6\times10^{-3}}{3.3\times10^{-19}} = 2\times10^{16}\,\text{photons s}^{-1} \] \[ \boxed{2\times10^{16}} \]