When a photosensitive metal surface is illuminated with radiation of… | MHT CET 2025 (22 Apr, Shift 1)

Q40MHT CET 2025 · 22 APR · SHIFT 1Medium

Photoelectric Effect: Einstein's Equation

When a photosensitive metal surface is illuminated with radiation of wavelength ' $\lambda_1$ ', the stopping potential is ' $V_1$ '. If the same surface is illuminated with radiation of wavelength ' $3\lambda_1$ ', the stopping potential is $\frac{V_1}{6}$ . The threshold wavelength for the photosensitive metal surface is

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Answer: (c)

$\frac{hc}{\lambda_1} - \phi = eV_1$ and $\frac{hc}{3\lambda_1} - \phi = \frac{eV_1}{6}$
Multiply the second by 6 and equate: $\frac{2hc}{\lambda_1} - 6\phi = \frac{hc}{\lambda_1} - \phi$
$5\phi = \frac{hc}{\lambda_1}$
$\lambda_0 = \frac{hc}{\phi} = 5\lambda_1$ . So the answer is (c).

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