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JEE Main 2017 (8 Apr, Shift 1) · Photoelectric Effect: Einstein's Equation

Photoelectric Effect: Einstein's Equation question from JEE Main 2017 (8 Apr, Shift 1)

Q139JEE Main 2017 · 8 APR · SHIFT 1Difficult

Photoelectric Effect: Einstein's Equation

The maximum velocity of the photoelectrons emitted from the surface is v when light of frequency n falls on a metal surface. If the incident frequency is increased to 3n, the maximum velocity of the ejected photoelectrons will be:

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Answer: (c)

$\frac{1}{2}mv^2 = hn - \phi$
$\frac{1}{2}mv'^2 = 3hn - \phi = 3(hn - \phi) + 2\phi = \frac{3}{2}mv^2 + 2\phi$
So $v'^2 > 3v^2$ , i.e. $v' > \sqrt{3}\,v$ .
So the answer is (c).

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