# A monochromatic source of light operating at 200 W emits 4×10^20 photons per second. Find the wavelength of the light.

Q: A monochromatic source of light operating at 200 W emits 4×1020 photons per second. Find the wavelength of the light.

Sol: Energy of photon , $\large E = \frac{P}{N/t}$

$\large E = \frac{200}{4 \times 10^{20}}$

E = 5 × 10-19 J