(a) Write the expression for the magnetic force acting on a k charged particle moving with velocity v in the presence of magnetic field B .
(b) A neutron an electron and an alpha particel moving with equal velocities enter a uniform magnetic field going into the plane of the paper as shown. Trace their paths in the field and justify your answer .

Explanation

(a) `vec(F ) =q (vec(v) xx vec(B))rArr f = qv B " sin " theta " where " theta` is angle between velocity and magnetic field .

(b) Force on `prop` particle will be
`F=2 e . ,v B (theta =90^(@)) =2 e v B`
This force will make the `prop` particle move on a circular path
As neutron does not have any charge so it will go undeviated .
Electron has negative charge so force will be opposite to that of `prop` particel and given by F = ev b