An electromagnet can create a uniform magnetic field in the +z direction. A loop of wire is initially placed in the x-y plane. What is the direction of the induced current while the electromagnet is turned on slowly?

A) Clockwise

B) Counterclockwise

C) Zero

D) Depends

Solution: A. As the electromagnet turns on, the external magnetic field increases in the +z direction. The area does not change, so the magnetic flux through the loop increases. The external field (+z) and the induced field (-z) must be opposite. The current must go clockwise to create the necessary field by the right-hand rule.