Wrong Answer
Initially I chose d. since the magnetic force is perpendicular to the velocity of the beam. But it was the wrong answer so I took it off from the choices.
A magnetic field deflects an electron beam, but it can not do any work on the beam. Why?
a. since the magnetic force on the beam is zero
b. since the acceleration of the beam is zero
c. since the magnetic force is perpendicular to the trace of the beam
d. none of them