A neutron, a proton, an electron and an `alpha-`particle enter a region of uniform magnetic field with equal velocities. The magnetic field is perpendicular to the paper and directed into it. The tracks of particles are labeled in Fig. 1.132. The neutron follows the track

Options

A. A
B. B
C. C
D. D

Answer

D

Explanation

A neutron is electrically neutral particle .It will pass undeflected ,therefore it follows track C.
Electron is a negatively charged particle.According to Fleming.s left hand rule,the magnetic force on the electron will be towards right.
Therefore ,it follow track D.
Proton and alpha particle are positively charged particles.In accordance with Fleming.s left hand rule magnetic force on these particles will be towards left.Among the tracks A and B,one is of proton and other of `alpha`-particle
As `r=(mv)/(Bq)`
`therefore (r_(alpha))/(r_(p))=(m_(alpha))/(m_(p))xx(q_(p))/(q_(alpha))=((4)/(1))((1)/(2))=2`
`r_(alpha)gtr_(p)`
Therefore,`alpha`-particle follows track B and proton follows track A.