An electron having charge 
and mass 
is accelerated from rest in a vacuum through a potential difference 
. The electron then enters a region of uniform magnetic field of magnetic flux density 
, as shown in the figure below.
The direction of the uniform magnetic field is into the plane of the paper. The velocity of the electron as it enters the magnetic field is normal to the magnetic field. The radius of the circular path of the electron in the magnetic field is 
.
Explain why the path of the electron in the magnetic field is the arc of a circle.
Show that the magnitude p of the momentum of the electron as it enters the magnetic field is given by
The potential difference is 
. The radius of the circular arc is 
. Determine the magnitude of the magnetic flux density.
of the momentum of the electron as it enters the magnetic field is shown to be given by
.
