Question

1. Which statement about the nature of electric and magnetic fields is the most accurate?

A)Fields can only ever be "electric" or "magnetic", regardless of reference frame.

B)Whether a field is seen as "electric" or "magnetic" depends on the motion of the reference frame relative to the sources of the field.

C)"Electric" and "magnetic" fields are entirely unrelated.

Answer 1

Option (B) is the correct answer.

Explanation:

When we apply the relativistic Fitzgerald-Lorentz contraction, even though the velocities involved are millimeters per second, the frame in which the wire is at rest, the positive and negative charge densities exactly balance, otherwise there will be extra electrostatic fields that the electrons will quickly move to neutralize. However, this necessarily means that the densities cannot balance exactly in the frame in which the drifting electrons are at rest.

The purely electrical force is identical in magnitude to the purely magnetic force in the other frame. So observers in the two frames will agree on the rate at which the particle accelerates away from the wire, but one will call the accelerating force magnetic, the other electric. We are forced to the conclusion that whether a particular force on an actual particle is magnetic or electric, or some mixture of both, depends on the frame of reference—so the distinction is rather artificial.