Question

A beam of light of wavelength 400 nm and power 1.55 mW is directed at the cathode of a photoelectric cell. If only $10\%$ of the incident photons effectively produce photoelectron, then find current due to these electrons.
(given, $hc=1240eV-nm,e=1.6\times {10}^{-19}C$)

• A. $5\mu A$
• B. $40\mu A$
• C. $50\mu A$
• D. $11.4\mu A$

Answer 1

Answer: (C)

$50\mu A$

Energy of incident photons $=\frac{hc}{\lambda }$

$=\frac{1240}{400}eV$

$=3.1eV$

$=4.96\times {10}^{-19}J$

Hence the frequency of incident photons is $\frac{1.55\times {10}^{-3}}{4.96\times {10}^{-19}}$ $=3.125\times {10}^{15}Hz$

Hence the photocurrent $=e\times \nu$

$=50\times {10}^{-6}A$

$=50\mu A$