When a certain metal surface is illuminated with a light of… | MHT CET 2026 (15 May, Shift 2)

Q12MHT CET 2026 · 15 MAY · SHIFT 2Medium

Photoelectric Effect: Einstein's Equation

When a certain metal surface is illuminated with a light of wavelength $\lambda$ , the stopping potential is $V$ . When the same surface is illuminated by light of wavelength $2\lambda$ , the stopping potential is $\left(\frac{V}{3}\right)$ . The threshold wavelength for the surface is

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Answer: (c)

$\frac{hc}{\lambda} - \phi = eV$ and $\frac{hc}{2\lambda} - \phi = \frac{eV}{3}$
Multiply the second by 3 and equate: $\frac{3hc}{2\lambda} - 3\phi = \frac{hc}{\lambda} - \phi$
$\frac{hc}{2\lambda} = 2\phi \Rightarrow \phi = \frac{hc}{4\lambda}$
$\lambda_0 = \frac{hc}{\phi} = 4\lambda$ . So the answer is (c) $4\lambda$ .

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