Question

A magnetic field exerts no force on

• A. an electric charge moving perpendicular to its direction
• B. an unmagnetized iron bar
• C. a stationary electric charge
• D. a magnet

Answer 1

The correct option is C

a stationary electric charge

Explanation of correct answer:

The correct answer is option (C).

1. Magnetic Force is given by the Lorentz equation as:
2. $F=q(V\times B)$, where $q$ is the amount of electric charge
3. Where, $V$ being the velocity of the charge and,
4. $B$ the magnetic flux.
5. So, for the stationary electric charge, the velocity of the charge will be zero which will eventually make the force zero.

Explanation of incorrect answer(s):

In the case of option (A),

1. the force will be $F=qVB\sin \left(90°\right)=qVB$ which is definitely not zero.

In the case of (B) and (D),

1. The force will not be zero as an unmagnetized iron bar and a magnet will possess some magnetic field around them which will in the end produce a force.

Thus, the correct answer is option (C).