IB Physics D3. Ex. 3. Circular motion of the electron in the magnetic field.

Motion of the electron in a magnetic field.
An electron, that has been accelerated from rest by a potential difference of 250 V, enters a region of magnetic field of strength 0.12 T that is directed into the plane of the page.
The electron’s path while in the region of magnetic field is a quarter circle. Show that the
(i) speed of the electron after acceleration is 9.4×10 m/s.
(ii) radius of the path is 4.5×10 m.
The diagram below shows the momentum of the electron as it enters and leaves the region of magnetic field.
The magnitude of the initial momentum and of the final momentum is 8.6×10 Ns.
(i) On the diagram above, draw an arrow to indicate the vector representing the change in the momentum of the electron.
(ii) Show that the magnitude of the change in the momentum of the electron is 1.2×10 Ns.
(iii) The time the electron spends in the region of magnetic field is 7.5 ×10 s. Estimate the magnitude of the average force on the electron.