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JEE Main 2020 (5 Sep, Shift 2) · Photoelectric Effect: Einstein's Equation

Photoelectric Effect: Einstein's Equation question from JEE Main 2020 (5 Sep, Shift 2)

Q122JEE Main 2020 · 5 SEP · SHIFT 2Easy

Photoelectric Effect: Einstein's Equation

The surface of a metal is illuminated alternately with photons of energies E1 = 4 eV and E2 = 2.5 eV respectively. The ratio of maximum speeds of the photoelectrons emitted in the two cases is 2. The work function of the metal in (eV) is _____.

Numerical answer type. Work it out, then open the answer.

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Answer: 2

$v_{max} \propto \sqrt{E - \phi}$ , so $\frac{v_1^2}{v_2^2} = \frac{4 - \phi}{2.5 - \phi} = 2^2 = 4$ .
$4 - \phi = 10 - 4\phi \Rightarrow 3\phi = 6$
Work function $\phi = 2$ eV.

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