Question

A 100 W point source emits monochromatic light of wavelength $6000\stackrel{o}{A}$. 1.5 mW of $400\stackrel{o}{A}$ light is directed at a photoelectric cell. If 0.10 per cent of the incident photons produce photoelectrons, find current in the cell. [Given $h=6.6\times {10}^{-34}Js,c=3\times {10}^{8}m{s}^{-1}$ and $e=1.6\times {10}^{-19}C$]

• A. $0.59\mu A$
• B. $1.16\mu A$
• C. $0.48\mu A$
• D. $0.79\mu A$

Answer 1

The correct option is C $0.48\mu A$

Number of photons emitted per unit time is given by:

$n=\frac{P\lambda }{hc}$

Number of photoelectrons produced

$N=n\times \frac{0.1}{100}=n\times {10}^{-3}$

Current is charge per unit time i.e.
$I=N\times 1.6\times {10}^{-19}A$

$I=1.6\times {10}^{-19}\frac{1.5\times {10}^{-3}\times 400\times {10}^{-10}\times {10}^{-3}}{6.6\times {10}^{-34}\times 3\times {10}^8}A$ $=0.48\mu A$