First slide

Photoelectric effect and study of photoelectric effect

Question

Silver has a work function of 4.7 eV. When ultraviolet light of wavelength 100 nm is incident upon it, a potential of 7.7 V is required to stop the photoelectrons from reaching the collector plate. How much potential will be required to stop the photoelectrons when light of wavelength 200 nm is incident upon silver?

Moderate

A

1.5 V
B

3.85 V
C

2.35 V
D

15.4 V

Solution

$\begin{array}{l} λ_{1} = \frac{12375}{E_{1} (eV)} Å = 1000 Å \\ ∴ E_{1} = 12.375 eV \\ Similarly, \frac{12375}{λ_{2} (Å)} eV = \frac{12375}{2000} = 6.1875 eV \\ Now, E_{1} - W_{0} = e V_{s} \\ and E_{2} - W_{0} = e V_{S} \\ Hence, 12.375 - W_{0} = 7.7 eV \\ and 6.1875 - W_{0} = e V_{s}^{'} \\ Solving, we get V_{s}^{'} = 1.5 V \end{array}$

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