When a charged particle moves in a magnetic field, does its kinetic energy always remain constant? Explain.

Explanation

The force on moving charged particle in a magnetic field, `vecF=q(vecvxxvecB)` is always perpendicular to `vecv` and `vecB`. Thus
work done `=FS cos 90^@=0`.
This means that a uniform magnetic field can do no work on charged particle although it can change its direction of motion. Hence the kinetic energy of charged particle in a magnetic field remains unchanged.