Magnetism

An electron, a proton and an alpha particle having the same kinetic energy are moving in circular orbits of radii re, rp, rα respectively in a uniform magnetic field B. The relation between re, rp, rα is :

  1. re < rp = rα
  2. re < rp < rα
  3. re < rα < rp
  4. re > rp = rα

Answer

Radius of circular path in magnetic field is given by

R = √(2Km)/qB

where

  • K = kinetic energy of particle
  • m = mass of particle
  • q = charge on particle
  • B = magnetic field intensity
  • R = radius of path

R ∝ √m/q

As me < mp

re < rp

rα ∝ √(4mp)/ 2qp

rα ∝ √(mp) / qp

rα = rp

The correct option is A.