A charged particle moving along the +x-axis enters a uniform magnetic field pointing along the +z-axis.A uniform electric field is also present.Due to the combined effect of both fields,the particle does not change its velocity.What is the direction of the electric field?
A)along the -y-axis
B)along the +y-axis
C)along the -x-axis
D)along the +x-axis
E)along the -z-axis

Question

Quizplus · Accepted Answer

In a uniform magnetic field, the charged particle moves in a circular path perpendicular to both the magnetic field and the velocity of the particle. Therefore, the magnetic force acting on the particle is perpendicular to its velocity. 
Since the velocity of the particle remains unchanged, the electric field must be acting in the opposite direction to cancel out the magnetic force.
Thus, the electric field must be pointing along the +y-axis, perpendicular to both the magnetic field (+z-axis) and the velocity of the particle (+x-axis).

A Charged Particle Moving Along the +X-Axis Enters a Uniform