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  4. 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

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Q. 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

NTA AbhyasNTA Abhyas 2022

Solution:

$E=W_{0}+eV_{0}$
For hydrogen atom, $E=+13.6\,eV$
$\therefore +13.6=4.2+eV_{0}$
$\Rightarrow V_{0}=\frac{\left(\right. 13 . 6 - 4 . 2 \left.\right) eV}{e}=9.4\,V$
Potential at anode $=-9.4\,V$