A monochromatic source of light operating at 15 kW emits $2.5 imes 10^{22}$ photons/s. The region

Question

A monochromatic source of light operating at 15 kW emits $2.5 \times 10^{22}$ photons/s. The region of an electromagnetic spectrum to which the emitted electromagnetic radiation belongs to $\_\_\_\_$ .

(Take $h = 6.6 \times 10^{- 34}\text{ }J.s$ and $c = 3 \times 10^{8}\text{ }m/s$ ).

Accepted Answer

Sol. [Key Concept: Photon energy $\frac{hc}{\lambda} = \frac{power}{photons/s}$ gives $\lambda \approx 3.3 	imes 10^{- 7}$ m ($330$ nm), which lies in the ultraviolet.]$${\frac{hC}{\lambda} = \frac{15 	imes 10^{3}}{2.5 	imes 10^{22}} }{	herefore\lambda = \frac{6.6 	imes 10^{- 34} 	imes 3 	imes 10^{8} 	imes 2.5 	imes 10^{22}}{15 	imes 10^{3}} }{\lambda = 3.3 	imes 10^{- 7} }$$

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