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JEE Main 2003 (AIEEE) · Photoelectric Effect: Einstein's Equation

Photoelectric Effect: Einstein's Equation question from JEE Main 2003 (AIEEE)

Q166JEE Main 2003 · AIEEEEasy

Photoelectric Effect: Einstein's Equation

Two identical photo-cathodes receive light of frequencies $f_1$ and $f_2$ . If the velocities of the photo electrons (of mass $m$ ) coming out are respectively $v_1$ and $v_2,$ then

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Answer: (a)

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 (a).

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