1. 23.3 Induction and the Electric Generator
If you move a magnet near a coil of wire, a current will be produced.
This process is called electromagnetic induction, because a moving magnet induces electric current to flow.
Moving electric charge creates magnetism and conversely, changing magnetic fields also can cause electric charge to move.

2. 23.3 Induction
Current is only produced if the magnet is moving because a changing magnetic field is what creates current.
If the magnetic field does not change, such as when the magnet is stationary, the current is zero.

3. 23.3 Induction
If the magnetic field is increasing, the induced current is in one direction.
If the field is decreasing, the induced current is in the opposite direction.

4. 23.3 Magnetic flux
A moving magnet induces current in a coil only if the magnetic field of the magnet passes through the coil.

5. 23.3 Faraday's Law
Faraday’s law says the current in a coil is proportional to the rate at which the magnetic field passing through the coil (the flux) changes.
Consider a coil of wire rotating between two magnets

6. 23.3 Faraday's Law
When the coil is in position (A), the magnetic flux points from left to right.
As thecoil rotates (B), the number of field lines that go through the coil decreases.
As a result, the flux starts to decrease and current flows in a negative direction.
At position (C), the largest negative current flows because the rate of change in
flux is greatest.
The graph of flux versus time has the steepest slope at position (C), and that is why the current is largest.
At position (C), no magnetic field lines are passing through the coil at all and therefore the flux through it is zero.
As the coil continues to rotate (D), flux is still decreasing by getting more negative.
Current flows in the same direction, but decreases proportionally to the decreasing rate of change (the slope of flux versus time levels out).
At position (E), the flux through the coil reaches its most negative value.
The slope of the flux versus time graph is zero and the current is zero.
As the coil rotates through (F), the flux starts increasing and current flows in the opposite direction.

7. 23.3 Generators
A generator is a device that uses induction to convert mechanical energy into electrical energy.
Because the magnet near the coil alternates from north to south as the disk spins,
the direction of the current reverses every time a magnet passes the coil.
This creates an alternating current.

8. 23.3 Transformers
Transformers are extremely useful because they efficiently change voltage and current, while providing the same total power.
The transformer uses electromagnetic induction, similar to a generator.

9. 23.3 Transformers
A relationship between voltages and turns for a transformer results because the two coils have a different number of turns.

10. Application: Trains that Float by Magnetic Levitation