Question

What does the magnetic field not interact with?
A.)Stationary permanent magnets
B.)Moving charges
C.)Stationary charges
D.)Moving permanent magnets

Answer 1

Hint: Recall the properties of a magnetic field. Also recall the Lorentz force law $(\overrightarrow{F}=q\overrightarrow{v}\times \overrightarrow{B})$

Complete step by step answer:

A magnetic field in general, interacts with other magnets, be it stationary or moving. The magnetic field applies a force on the magnets such that they tend to line up along the magnetic lines of force in the magnetic field.
A magnetic field also interacts with moving electric charges which have some non-zero velocity.

 This is described in the Lorentz force law, according to which, a moving electric charge in a magnetic field experiences a force that is perpendicular to the plane containing the velocity of the electric charge and the magnetic field. The magnitude of this force is dependent on the magnitudes of the velocity of the electric charge and the magnetic field by the relation:

$\overrightarrow{F}=q\overrightarrow{v}\times \overrightarrow{B}$
$\therefore F=qvB\sin \theta$

Where F is the Lorentz force vector on the charge, v is the velocity vector of the charge and B is the magnetic field vector, q is the magnitude of charge on the particle and θ is the angle between v and B. Thus, we can see that if the charge is stationary then v will be zero and hence, the force on the particle will automatically become zero.
Thus, a magnetic field does not interact with a stationary electric charge.
So the correct answer is C) stationary charges.

Note: A student might not have his basics clear and think that a magnetic field interacts with all kinds of charged bodies, irrespective of motion. This may lead to a mistake.
Also, he may not be familiar with moving permanent magnets, since they are not too mainstream and may not be completely aware of their behavior in other magnetic fields.