Question

why is work done on moving charge particle in a magnetic field zero?​

Answer 1

The answer follows from the expression for the force F on a particle with charge q moving with velocity v in a magnetic field B

F = q ( v x B )

Since the force F due to the magnetic field is perpendicular to v the force will alter the path of the particle, but the work done by this force on the particle will be zero.

Answer 2

Answer:

For a moving charge the magnetic force is always perpendicular to the motion(velocity) of the charged particle. Since forces perpendicular to the velocity does zero work because the force velocity dot product will become zero.