﻿ A 5-W point-source emits monochromatic light of wavelength 5000 Å. How many photons per second strike a unit area placed 5 m away from the source and illuminated by it? What should be the work function of the metal from whose surface this light can liberate photoelectrons?     : Kaysons Education

# A 5-W Point-source Emits Monochromatic Light Of Wavelength 5000 Å. How Many Photons Per Second Strike A Unit Area Placed 5 m away From The Source And Illuminated By It? What Should Be The Work Function Of The Metal From Whose Surface This Light Can Liberate Photoelectrons?

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## Question

### Solution

Correct option is

The energy of an emitted photon is

.

The power of the source is 5 W, that is, the rate of emission of light is 5 Js–1. Since the energy of one light-photon is , the number of photons emitted per second from the source is

The number of photons striking per second per unit area placed 5 m (= R, say) away from the source is

Now,

Work function of the metal = energy of incident photon

= 2.475 eV.

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