Q. A beam of electron passes undeflected through mutually perpendicular electric and magnetic fields. If the electric field is switched off, and the same magnetic field is maintained, the electrons move
A) in a circular orbit
B) along a parabolic path
C) along a straight line
D) in an elliptical orbit
Explanation
[Solution from source] With only the magnetic field, the force qv × B is always perpendicular to the velocity, which is itself perpendicular to B, so the electrons move in a circle. A parabolic path needs a constant force such as an electric field, which has been switched off. Answer (1).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.