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JEE Main 2024 (31 Jan, Shift 1) · Photoelectric Effect: Einstein's Equation

Photoelectric Effect: Einstein's Equation question from JEE Main 2024 (31 Jan, Shift 1)

Q65JEE Main 2024 · 31 JAN · SHIFT 1Medium

Photoelectric Effect: Einstein's Equation

When a metal surface is illuminated by light of wavelength $\lambda$ , the stopping potential is $8\text{ V}$ . When the same surface is illuminated by light of wavelength $3\lambda$ , stopping potential is $2\text{ V}$ . The threshold wavelength for this surface is:

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Answer: (b)

$A - \phi = 8\text{ eV}$ and $\frac{A}{3} - \phi = 2\text{ eV}$ , with $A = \frac{hc}{\lambda}$
Subtract: $\frac{2A}{3} = 6 \Rightarrow A = 9\text{ eV},\ \phi = 1\text{ eV}$
$\lambda_0 = \frac{hc}{\phi} = 9\lambda$
So the answer is (b) $9\lambda$ .

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