Question

A moving charge will gain kinetic energy due
to the application of :-
(1) Electric field
(2) Magnetic field
(3) Both of these
(4) None of these

Answer 1

Electric field.
Many people think that the magnetic field should also be able to change the energy of a charged particle, but that is not so. The kinetic energy of a charged particle does not change at non - relativistic speeds and since the mass won't either, the KE remains constant.

Another way to look at it is to say that the magnetic force on the particle is at right angles to the direction the particle is travelling. Therefore, the direction of speed changes but not the magnitude. 1/2 m v^2 remains the same in a magnetic field.

Magnetic field means no change in energy, because there is no change in speed.