Question

a proton and an alpha particle enter at right angles into a uniform magnetic field . if the radius of circular orbits are equal

Answer 1

Alpha particle will be helium nucleus of charge 2e and mass 4u

Proton will be hydrogen of charge 1e and mass 1u

Radius of circle of charged particle in magnetic field will be r=mv/qb

By lorentz force,

Radius=momemtum /charge *magnetic field

WE know that radius is inversly proportional to charge 

SO Radius of alpha particle will be half of radius of proton

Hence Radii =1:2.