Test: Motion in Combined Electric & Magnetic Fields - JEE MCQ

if the particle is undeflected, then the magnetic force equals the electric force:
q x v x B=q x E
B is the magnitude of the magnetic field
E is the magnitude of the electric field
v is the magnitude of the velocity of the particle.
If the forces are equal then:
v=E/B
For undeflected v=1
E/B=1

We also know for a circular motion time period = 2πm/qb as the charge in question has. Constant q, mass is also constant, b is also constant thus time period for semicircular path is constant.

If a charged particle goes unaccelerated in a region containing
electric and magnetic fields,

Dipole moment of a current loop 
M=N ×I × A
So, it is dependent on current in the loop, number of turns and area of the loop.
It is independent of the magnetic field in which it is situated.
 

The magnetic force acts perpendicular to the velocity of the particle. This  causes circular motion. In the magnetic field the speed and kinetic energy of the particle remain constant, but the direction is altered at each instant by the perpendicular magnetic force.