According to Faraday's law and Lenz's law, the induced emf will do which of the following with respect to changes in magnetic flux?

• A. It enhances the change in magnetic flux.
• B. It depends on the square of the rate of change of flux.
• C. It opposes the change in magnetic flux.
• D. It exists only when there is a changing magnetic flux and an accompanying electric field.

Answer: (C)

The induced emf acts to oppose the change in magnetic flux. Faraday’s law gives emf = - dΦB/dt, and the minus sign is exactly Lenz’s law in action: the induced current (and its associated magnetic field) acts to oppose how the flux is changing through the loop.

If the magnetic flux through the loop is increasing, the induced current generates a magnetic field that points to reduce that increase. If the flux is decreasing, the induced current produces a field that helps keep the flux from dropping. The magnitude of the emf is proportional to the rate at which the flux changes, not the square of that rate, and it vanishes when the flux is constant.

So the best description is that the induced emf opposes the change in magnetic flux.