An electron is moving in a circular orbit in a uniform magnetic field. is the kinetic energy of the electron changing? select the correct answer and explanation. a: no because the force is always perpendicular to the velocity. b: no because the force is always parallel to the velocity. c: yes because the force is always parallel to the velocity. d: yes because the force is always perpendicular to the velocity.

A: No because the force is always perpendicular to the velocity

Explanation:

The magnetic force does not do any work on the electron. In fact, the work done by the magnetic force is given by:

where

F is the magnetic force

d is the displacement of the electron

is the angle between the direction of the force and the direction of motion of the electron

The magnetic force, however, is always perpendicular to the velocity (and so the direction) of the charged particle: this means that , so and the work done is zero.

According to the work-energy theorem, the change in kinetic energy of the electron is equal to the work done on it:

and so, since the work done is zero, the kinetic energy does not change.