Force on moving charges: An electron, moving toward the west, enters a uniform magnetic field. Because of this field the electron curves upward. The direction of the magnetic field is

Question

Quizplus · Accepted Answer

According to Fleming's left-hand rule, when a charge moves in a magnetic field, the magnetic force on the charge is perpendicular to both the direction of motion of the charge and the direction of the magnetic field. In this case, the electron is curving upward which means the magnetic force is perpendicular to the plane of motion of the electron and directed towards the north. Therefore, the direction of the magnetic field is towards the north (choice A).

Force on Moving Charges: an Electron, Moving Toward the West