Question

The plane of a flat, circular loop of wire is horizontal. An external magnetic field is directed perpendicular to the plane of the loop. The magnitude of the external magnetic field is increasing with time. Because of this increasing magnetic field, an induced current is flowing clockwise in the loop, as viewed from above. What is the direction of the external magnetic field? Justify your conclusion.

Answer 1

According to Lenz’s law, the induced current itself creates a magnetic field to oppose the change in the external magnetic field.

Using the right hand rule, the clockwise current creates a magnetic field vertically downward.

By Lenz’s law, the created magnetic field points downward in response to...

if the external magnetic field points upward and is increasing in strength...

or points downward and is decreasing in strength.

We are told the external field is increasing in strength, so its direction must be vertically upward.