Question

In the photoelectric experiment, if we use a monochromatic light, the I-V curve is as shown. If work function of the metal is 2eV, estimate the power of light used. (Assume efficiency of photo emission `=10^(-3)%`, i.e. number of photoelectrones emitted are `10^(-3)%` of number of photons incident on metal.)

Answer 1

Correct Answer - 7
The energy of incident photons is given by
`hc =eV_(s)+phi_(0)=2+5=7eV`
(`V_(s)` is stopping potential and `phi_(0)` is work function)
Saturation current `= 10_(-5) A=(etaP)/(hv)e=(10^(-5)P)/(7 xx e)e`
(`eta` is photo emission efficiency) `:. P = 7 W`.