JEE Main 2025 Jan 22 Shift 2, Physics Q10: Introduction and Photoelectric Effect

JEE Main2025Jan 22, Shift 2Physics

A light source of wavelength $λ$ illuminates a metal surface and electrons are ejected with maximum kinetic energy of 2 eV. If the same surface is illuminated by a light source of wavelength $\frac{λ}{2}$ , then the maximum kinetic energy of ejected electrons will be (The work function of metal is 1 eV)

A
2 eV
B
6 eV
C
5 eV
D
3 eV

Solution

Einstein's photoelectric equation: $\frac{h c}{λ} = ϕ + K_{m a x}$ .

With wavelength $λ$ : $\frac{h c}{λ} = 1 + 2 = 3 eV$ .

With wavelength $λ /2$ , the photon energy doubles:

$\frac{h c}{λ /2} = 2 \cdot \frac{h c}{λ} = 6 eV$ .

Applying the photoelectric equation again:

$6 = 1 + K_{m a x}^{'} \Rightarrow K_{m a x}^{'} = 5 eV$ .

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JEE Main 2025 Jan 22 Shift 2, Physics Q10: Introduction and Photoelectric Effect

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