Question

A charged paricle goes undeflected in a region containing electric and magnetic field. It is possible that
A. `vecE||vecB,vecv||vecE`
B. `vecE` is not parallel to `vecB`
C. `vecv||vecB but vecE` is not parallel to `vecB`
D. `vecE||vecB but vecv` is not parallel to `vecE`

Answer 1

Correct Answer - (a,b)
If electric field is parallel to magnetic field,the charged particle
moving parallel to `vecE` experiences a forces in the direction of `vecE`.
due to `vecB` there will not be any force.
Hence, no deflection
The particle may go undeflected in the case when forces due to electric field and magnetic field balance each other.