First slide

Photoelectric effect and study of photoelectric effect

Question

The threshold frequency for certain metal is v₀. When light of frequency 2v₀ is incident on it, the maximum velocity of photoelectrons is 4 x 10⁶ ms^-1. If the frequency of
incident radiation is increased to 5v₀, then the maximum velocity of photoelectrons will be

Moderate

A

$4 / 5 \times 10^{6} {ms}^{- 1}$
B

$2 \times 10^{6} {ms}^{- 1}$
C

$8 \times 10^{6} {ms}^{- 1}$
D

$2 \times 10^{7} {ms}^{- 1}$

Solution

In the first case,
$\frac{1}{2} m v_{1 max}^{2} = 2 h v_{0} - h v_{0} = h v_{0}$
In the second case
$\frac{1}{2} m v_{2 max}^{2} = 5 h v_{0} - h v_{0} = 4 h v_{0}$
$Clearly, v_{2 max} is double of v_{1 max} \Rightarrow v_{2 max} = 2 v_{1 max} = 8 \times 10^{6} {ms}^{- 1}$

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