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 $- x$-axis
B) along the $+ y$-axis
C) along the $+ x$-axis
D) along the $- z$-axis
E) along the $- y$-axis

Question

Quizplus · Accepted Answer

The electric field must be along the $+ y$-axis to balance the magnetic force which acts perpendicular to both the velocity (along $+ x$-axis) and the magnetic field (along $+ z$-axis), ensuring the particle does not change its velocity.

A Charged Particle Moving Along The +x+ x+x -Axis Enters a Uniform Magnetic Field Pointing Along The

A Charged Particle Moving Along The $+ x$ -Axis Enters a Uniform Magnetic Field Pointing Along The