Question

A charged particles enters along the axis of a current carrying a long solenoid, How is its velocity affected? Will the particle be accelerated or decelerated?

Answer 1

The magnetic field due to a current in solenoid is along the axis,

so when a charged particle enters along the axis

$(\theta =0)$, the magnetic force on particle is

$qvB\sin 0^o=0$; so the particle's velocity remains unchanged

i.e., the particle remains unaccelerated.