A beam of electrons passes undeflected through uniformly perpendicular electric and magnetic fields. If the electric field is switched off, and the same magnetic field is maintained then the electrons move:

Options

A. in an elliptical orbit
B. in a circular orbit
C. along a parabolic path
D. along a straight line

Answer

B

Explanation

If both electric and magnetic field are present and perpendicular to each other and the particle is moving perpendicular to both of them with `F_(e)=F_(m)`. In this situation `vec(E) ne 0` and `vec(B)ne0`
but if electric field becomes zero, then only force due to magnetic field exists. under this force, the charge moves along a circle.