JEE Main 2026 Apr 8 Shift 2, Physics Q18: Introduction and Photoelectric Effect

JEE Main2026Apr 8, Shift 2Physics

$K_{1}$ and $K_{2}$ be the maximum kinetic energies of photoelectrons emitted from a surface of a given material for the light of wavelength $λ_{1}$ and $λ_{2}$ , respectively. If $λ_{1} = 2 λ_{2}$ then the work function of material is given by :

A
$K_{2} + 2 K_{1}$
B
$2 K_{2} - K_{1}$
C
$K_{1} - 2 K_{2}$
D
$K_{2} - 2 K_{1}$

Solution

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

For $λ_{1} = 2 λ_{2}$ : $K_{1} = \frac{h c}{2 λ _{2}} - ϕ$ .

For $λ_{2}$ : $K_{2} = \frac{h c}{λ _{2}} - ϕ$ .

Multiplying the first equation by $2$ : $2 K_{1} = \frac{h c}{λ _{2}} - 2 ϕ$ .

Subtracting from the second: $K_{2} - 2 K_{1} = - ϕ + 2 ϕ = ϕ$ .

$∴$ $ϕ = K_{2} - 2 K_{1}$ .

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JEE Main 2026 Apr 8 Shift 2, Physics Q18: Introduction and Photoelectric Effect

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