A monochromatic source emitting light of wavelength 600 nm has a power output of 66 W. The number of photons emitted by the source in 2 minutes is: (Given: $h = 6.6 × 10^{-34} Js$)

$2.4 × 10^{22}$

The correct answer is Option (2) → $2.4 × 10^{22}$

Wavelength of light: $\lambda = 600 \times 10^{-9}\, \text{m}$

Power of source: $P = 66 \, \text{W}$

Time: $t = 2 \times 60 = 120 \, \text{s}$

Total energy emitted: $E_\text{total} = P \cdot t = 66 \times 120 = 7920 \, \text{J}$

Energy of one photon: $E_\text{photon} = \frac{hc}{\lambda}$

$h = 6.63 \times 10^{-34} \, \text{Js}, \; c = 3 \times 10^8 \, \text{m/s}$

$E_\text{photon} = \frac{6.63 \times 10^{-34} \cdot 3 \times 10^8}{600 \times 10^{-9}}$

$E_\text{photon} = \frac{1.989 \times 10^{-25}}{6 \times 10^{-7}} = 3.315 \times 10^{-19} \, \text{J}$

Number of photons: $N = \frac{E_\text{total}}{E_\text{photon}} = \frac{7920}{3.315 \times 10^{-19}}$

$N \approx 2.39 \times 10^{22}$

Answer: $2.39 \times 10^{22}$ photons