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JEE Main 2020 (3 Sep, Shift 1) · Photoelectric Effect: Einstein's Equation

Photoelectric Effect: Einstein's Equation question from JEE Main 2020 (3 Sep, Shift 1)

Q124JEE Main 2020 · 3 SEP · SHIFT 1Medium

Photoelectric Effect: Einstein's Equation

When the wavelength of radiation falling on a metal is changed from 500 nm to 200 nm, the maximum kinetic energy of the photoelectrons becomes three times larger. The work function of the metal is close to:

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Answer: (c)

Photon energies ( $hc = 1240$ eV nm): $\frac{1240}{500} = 2.48$ eV, $\frac{1240}{200} = 6.2$ eV.
$3(2.48 - \phi) = 6.2 - \phi \Rightarrow 7.44 - 3\phi = 6.2 - \phi$
$2\phi = 1.24 \Rightarrow \phi \approx 0.62$ eV
So the answer is (c) 0.61 eV.

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