If a charged particle of charge to mass ratio $\alpha$ enters in a magnetic field of strength B at a speed $\mathrm{v}=\left(2\mathrm{\alpha d}\right)\left(\mathrm{B}\right),$ then

the time for which particle will be in the magnetic field is $\frac{2\mathrm{\pi }}{\mathrm{\alpha B}}$

the charge will move on a circular path and then will come out from magnetic field at some distance from the point of insertion

angle subtended by the path of charge particle in magnetic field at the centre of circular path is $\pi /2$

angle subtended by the path of charge particle in magnetic field at the centre of circular path is $2\pi$.