According to my text book:
The Lorentz Force F on a charged particle moving in an electromagnetic field is given by:
$$F= qE + q(v\times B)$$
then it states that "it is to be pointed out that only the electric force does work, while the no work is done by the magnetic force which is simply a deflecting force."
How can this by true won't the the magnetic force have a considerable magnitude, will it now impart kinetic energy to the charge? Any explanations will help a lot. Please keep the terminology simple, thanks.
Best Answer
Work is done at a rate of $\vec{F} \cdot \vec{v}$. So any force component perpendicular to the velocity at all times cannot do any work classically. The kinetic energy remains unchanged because for the kinetic energy, only the magnitude of the velocity and not its direction is important. All that magnetic force does is change the direction of the velocity while keeping the velocity magnitude constant and that does not need any work.