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.)

Options

A. 2W
B. 5W
C. 7W
D. 10 W

Answer

C

Explanation

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