Question
If a charged particle kept at rest experiences an electromagnetic force:
  1. The electric field must not be zero.
  2. The magnetic field must not be zero.
  3. The electric field may or may not be zero.
  4. The magnetic field may or may not be zero.

Answer

  1. The electric field must not be zero.
  1. The magnetic field may or may not be zero.

Explanation:

Since particle is at rest, i.e. v=0, hence Fm=0

For electric force, E≠0

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