First slide

Photoelectric effect and study of photoelectric effect

Question

Light from a hydrogen discharge tube is incident on the cathode of a photoelectric cell. The work function of the cathode surface is 4.2 eV. In order to reduce the photocurrent to zero the voltage of the anode relative to the cathode must be made

Moderate

A

-4.2 V
B

-9.4 V
C

-17.8 V
D

+9.4 V

Solution

$E = W_{0} + e V_{0}$
For hydrogen atom, $E = + 13.6 eV$
$\begin{array}{l} ∴ + 13.6 = 4.2 + e V_{0} \\ \Rightarrow V_{0} = \frac{(13.6 - 4.2) e V}{e} = 9.4 V \\ Potential at anode = - 9.4 V \end{array}$

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