Question

An electron enters a magnetic field at right angles to it as shown in fig. The direction of the force acting on the electron will be:

(a) to the right,

(b) to the left,

(c) out of the page,

(d) into the page.

Answer 1

When a force conductor carrying current is placed perpendicular to the direction of magnetic field, the magnetic field acting on it is given by Flemings's left hand rule. Since the direction of current is the same as that of the motion of a positive charge, the direction of force acting on it when moving perpendicular to the direction of magnetic field is the same as that acting on a current-carrying conductor placed perpendicular to the direction of magnetic field. Obviously, the force acting on an electron is opposite to that. Therefore in this case it is into the page.