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JEE Main 2021 (17 Mar, Shift 2) · Photoelectric Effect: Einstein's Equation

Photoelectric Effect: Einstein's Equation question from JEE Main 2021 (17 Mar, Shift 2)

Q102JEE Main 2021 · 17 MAR · SHIFT 2Easy

Photoelectric Effect: Einstein's Equation

Two identical photocathodes receive the light of frequencies f1 and f2 respectively. If the velocities of the photo-electrons coming out are v1 and v2 respectively, then

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Answer: (d)

Same cathode, same $\phi$ : $\frac{1}{2}mv_1^2 = hf_1 - \phi$ and $\frac{1}{2}mv_2^2 = hf_2 - \phi$ .
Subtract: $\frac{1}{2}m(v_1^2 - v_2^2) = h(f_1 - f_2)$
$v_1^2 - v_2^2 = \frac{2h}{m}(f_1 - f_2)$
So the answer is (d).

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