JEE Main 2021PhysicsDual Nature of MatterHardNumerical

JEE Main 2021 — Dual Nature of Matter Question with Solution

JEE Main 2021 (25 Jul Shift 2)

Question

A light beam of wavelength 500 nm is incident on a metal having work function of 1.25 eV, placed in a magnetic field of intensity B. The electrons emitted perpendicular to the magnetic field B, with maximum kinetic energy are bent into a circular arc of radius 30 cm. The value of B is ________×10-7 T.
Given hc=20×10-26 J m, the mass of the electron=9×10-31 kg.

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Show full solutionCorrect answer: 125
Correct answer
125

Step-by-step explanation

By photoelectric equation

hcλ-ϕ=kmax

kmax=1240500-1.25≈1.25

r=2mkeB

B=2mker

=125×10-7 T

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About this question

This is a previous-year question from JEE Main 2021, covering the Dual Nature of Matter chapter of Physics. PrepSharp catalogues every PYQ from JEE Main with a verified answer key and step-by-step solution prepared by IIT alumni — so you can search by chapter, topic or year and revise efficiently.