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Photoelectron moving in a magnetic field: work function from the radius of its path

This type of question, asked 3 times: 2021 Paper 11, 26 Jun 2022, 2 Apr 2025. All 3 questions below, oldest first.

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  1. Question 1

    2021 Paper 11

    9
    Light emitted by hydrogen gas corresponding to transition from n=3n = 3 to n=2n = 2 incident on a metal plate. The electron emitted from metal plate with maximum kinetic energy enters a magnetic field 5×10−4 T5 \times10^{- 4}\text{ }T perpendicularly. If the radius of path of electron is 7 mmmm then find the work function of metal.

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  2. Question 2

    26 Jun 2022

    107
    A metal surface is illuminated by a radiation of wavelength 4500Å4500\text{Å}. The ejected photo-electron enters a constant magnetic field of 2mT2mT making an angle of 90∘90^{\circ} with the magnetic field. If it starts revolving in a circular path of radius 2 mm2\text{ }mm, the work function of the metal is approximately:

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  3. Question 3

    2 Apr 2025

    20
    A monochromatic light is incident on a metallic plate having work function ϕ\phi. An electron, emitted normally to the plate from a point AA with maximum kinetic energy, enters a constant magnetic field, perpendicular to the initial velocity of electron. The electron passes through a curve and hits back the plate at a point B . The distance between A and B is : (Given : The magnitude of charge of an electron is e and mass is m,hm,h is Planck's constant and c is velocity of light. Take the magnetic field exists throughout the path of electron)

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