In an experiment on photoelectric effect light of wavelength `400 nm` is incident on a metal plate at rate of `5W.` The potential of the collector plate is made sufficiently positive with respect to emitter so that the current reaches the saturation value. Assuming that on the average one out of every `10^6` photons is able to eject a photoelectron, find the photocurrent in the circuit.

Explanation

Given ` lambda = 400 nm `,
` P = 5W `
` E of 1 photon ` = hc / lambda = (1242 / 400)eV`
Number of leectrons ` = 5 / Energy of 1 photon `
` = 5 xx 400/ 1.6 xx 10^(19) xx 1242`
Numbers of electrons `= 1 Per 10^(6) photon `
No. of photoelectrons emitted
` = 5 xx 400 / 1.6 xx 1242 xx 10^(-19) xx 10^(6) `
Photo electric current ` = 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 muA `