Question

A charge particle enters a uniform
magnetic field with its initial velocity
directed (in parallel to the field (ii)
Perpendicular to the field show that
no Change in the kinetic
energy of the particle in both cases
​

Answer 1

The work done by magnetic field on a charged particle is always zero. This is because the force due to the field is always acting in a direction perpendicular to the motion of the particle.

So,

W = FScos90 = 0

now, as the work done is given as the change in kinetic energy

W = dKE = 0

so, there will be no change in kinetic energy of the particle irrespective of where it enters the magnetic field.

Also this would mean that the particle would follow a circular trajectory inside a magnetic field.