JEE Main | 2018Work, Power and EnergyHard

Question

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:-

Options

A.

re < rp = rα

B.

re < rp < rα

C.

re < rα< rp

D.

re > rp = rα

Solution

Radius of circular path in magnetic field is given
by R = 3 KmqB
where K = kinetic energy of particle
m = mass of particle
q = charge on particle
B = magnetic field intensity
R = radius of path
For electron
re=2 K meeB  ...(i)
For proton
rp=2 K mpeB  ...(ii)
For α particle
rα=2KmαqαB=2K 4mp2eB=2KmpeB ...(iii)
as me < mp so re < rp = rα

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