JEE Main 2025 Jan 23 Shift 2, Physics Q6: Introduction and Photoelectric Effect

JEE Main2025Jan 23, Shift 2Physics

In photoelectric effect an em-wave is incident on a metal surface and electrons are ejected from the surface. If the work function of the metal is $2.14$ eV and stopping potential is $2$ V, what is the wavelength of the em-wave?

(Given $h c = 1242$ eV $\cdot$ nm where $h$ is the Planck's constant and $c$ is the speed of light in vaccum.)

A
$400$ nm
B
$600$ nm
C
$200$ nm
D
$300$ nm

Solution

Einstein's photoelectric equation gives $e V_{s} = E_{p h o t o n} - ϕ$ .

$E_{p h o t o n} = e V_{s} + ϕ = 2.0 + 2.14 = 4.14$ eV.

$λ = \frac{h c}{E _{p h o t o n}} = \frac{1242 eV \cdot nm}{4.14 eV} = 300$ nm.

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JEE Main 2025 Jan 23 Shift 2, Physics Q6: Introduction and Photoelectric Effect

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