First slide

Photoelectric effect and study of photoelectric effect

Question

Photons with energy 5eV are incident on a cathode C, on a photoelectric cell. The maximum energy of the emitted photoelectrons is 2eV. When photons of energy 6eV are incident on C, no photoelectrons will reach the anode A if the potential of A relative to C is

Moderate

A

3V
B

-3V
C

-1V
D

4V

Solution

Given Photon energy= 5eV
The maximum energy= 2eV
From the Einstein’s photo electric equation, we get
$ϕ = k_{\max} - E_{ϕ}$
$∴ ϕ = 5 - 2 = 3 eV$
Now, when photons of energy 6eV are incident, no photoelectrons are emitted. This is because a stopping potential is applied.
$\begin{array}{l} ∴ e V_{0} = E_{ϕ} - ϕ = 6 - 3 = 3 eV \\ V_{0} = 3 V \end{array}$
Hence, a stopping potential of 3V has to be applied.
Now, stopping potential is defined as the negative potential applied to the anode with respective to the cathode. Hence, stopping potential of A with respective C is -3V
So, the correct option is (B)

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