Question

Consider an electron entering a region between two charged metal plates where, aside from the electric field E, there is also a constant magnetic field B directed into the paper. V is the velocity of the electron (from left to right direction).

a)Write an expression for the electric and magnetic force.

b) It is observed that if B= 1.5 T and E=5.5 x 10^3 V/m, the electron keeps moving in a straight line. Find the speed of the electron (Assume there is no effect of gravity)

Answer 1

a) The electric force is e E, in the drection of the positive plate. The magnetic force is e V B, perpendicular to V and B

b) If the electron is moving parallel to the plates, the B force and E force can be in opposite directions, cancelling each other out when V*B = E

V = E/B = 3670 m/s