First slide

Photoelectric effect and study of photoelectric effect

Question

The KE of the photoelectrons is E when the incident wavelength is $λ$ /2. The KE becomes 2E when the incident wavelength is $λ$ /3. The work function of the metal is

Moderate

A

hc/ $λ$
B

2hc/ $λ$
C

3hc/ $λ$
D

hc/3 $λ$

Solution

$\begin{array}{l} C a s e 1 : E = \frac{h c}{λ / 2} - ϕ_{0} \\ C a s e 2 : 2 E = \frac{h c}{λ / 3} - ϕ_{0} \\ ⇒ 2 (\frac{2 h c}{λ} - ϕ_{0}) = \frac{3 h c}{λ} - ϕ_{0} \\ ⇒ \frac{4 h c}{λ} - 2 ϕ_{0} = \frac{3 h c}{λ} - ϕ_{0} \\ \Rightarrow ϕ_{0} = \frac{h c}{λ} \end{array}$

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