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Question
In an experiment on photoelectric effect, light of wavelength 400 nm is incident on a cesium plate at the rate of 5.0 W. The potential of the collector plate is made sufficiently positive with respect to the emitter, so that the current reaches its saturation value. Assuming that on average, one out of every 106 photons is able to eject a photoelectron, find the photocurrent in the circuit.
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Solution
Given:-
Wavelength of light, λ = 400 nm
Power, P = 5 W
Energy of photon,
`E = (hc)/λ = (1242/400) "eV"`
Number of photons, n = `P/E`
`n = (5 xx 400)/(1.6 xx 10^-19 xx 1242)`
Number of electrons = 1 electron per 106 photons
Number of photoelectrons emitted,
`n' = (5 xx 400)/(1.6 xx 1242 xx 10^-19 xx 10^6)`
Photo electric current,
I = Number of electron `xx` Charge on electron
`I = (5 xx 400)/(1.6 xx 1242 xx 10^-19 xx 10^6) xx 1.6 xx 10^-19`
`= 1.6 xx 10^-6 "A" = 1.6 "uA"`
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