Magnetic Induction

Key Points about Induction

If the current in the primary circuit is constant, then the current in the secondary circuit is zero.

When the magnetic field in the secondary circuit increases the current flows in one direction, and when the magnetic field decreases the current flows in the opposite direction.

The magnitude of the induced current and emf are proportional to the rate of change of the magnetic field.

Induced Current Produced by a Moving Magnet

The Magnetic Flux Through a Loop

Magnetic Flux

Find the flux through each side of the box.

Which flux(es) change(s) with time?

When will the emf and the magnetic flux be the greatest?

A Dynamic Microphone

The Pickup on an Electric Guitar

Magnetic Tape Recording

Induction Loop for the Hearing Impaired

Applying Lenz’s Law to a Magnet Moving Toward and Away From a Current Loop

The polarity of the induced emf in a loop is such that it produces a current whose magnetic field opposes the change in magnetic flux through the loop. That is, the induced current is in a direction such that the induced magnetic field attempts to maintain the original flux through the loop.

How do the accelerations compare?

Lenz’s Law Applied to a Decreasing Magnetic Field

Motional emf

Which plate is positively charge if the field increases?

What are the induced currents if I increases?

Eddy Currents

Quantitative Information from Lenz and Faraday

Find |B|, |F|, W, E, i, and |v|.

What are the induced current and the speed of the rod?

An Electric Generator

A Simple Electric Motor

Induced emf of a Rotating Coil