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

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Q. In the photoelectric experiment, if we use a monochromatic light, the $I-V$ curve is as shown. If work function of the metal is $2\, eV$, estimate the power of light used (in $W$). (Assume efficiency of photoemission $=10^{-3} \%$, i.e. number of photoelectrons emitted are $10^{-3} \%$ of number of photons incident on metal.)Physics Question Image

Dual Nature of Radiation and Matter

Solution:

The energy of incident photons is given by
$h v=e V_{s}+\phi_{0}=2+5=7\, eV$
( $V_{S}$ is stopping potential and $\phi_{0}$ is work function)
$\Rightarrow$ Saturation current $=10^{-5} A$
$=\frac{\eta P}{h v} e=\frac{10^{-5} P}{7 \times e} e$
Thus $P=7\, W$