The fact that the magnetic field generates a force perpendicular to the instantaneous velocity of the particle has implications for the work that the field does on the particle. As a consequence, if only the magnetic field acts on the particle, its kinetic energy will .

kinetic energy remains constant.

Explanation: The force on the charged particle is always perpendicular to the direction of its movement. Also, magnetic forces cause charged particles to change their direction of motion, but they do not change the speed of the particle. If the force is perpendicular to the motion, then no work is done. Hence magnetic forces do no work on charged particles and cannot increase their kinetic energy. Kinetic energy is therefore remain constant.