Chapter 22:

Induction and

Alternating Currentpp 793 - 820

Essential Questions

How can current be produced without a power source?

How do motors work?

How is mechanical energy converted to electrical energy?

Objective(s): We will be able to…

Describe how a magnetic field can induce current in a wire.

Describe how an electric motor relates to an electric generator.

Agenda:

Sorry, no building motors today due to technical difficulties! Tomorrow instead.

Check and review Magnets homework.

Intro to Inductance:

Notes: Magnetic Fields and Induced EMFs Generators Motors

Electromagnetic Induction Current in a circuit can be induced without the

use of a battery or voltage source.

We know that magnets cause electrons to move and realign, sooo… If a magnet moves closer to a circuit… Or a circuit is moved closer to a magnet…

If there is any relative motion between a circuit and a magnet, current is induced in the circuit.

Electromagnetic Induction

The angle between the magnetic field and the circuit affects induction.

(The blue dots are magnetic field lines coming out of the page)

The closer to perpendicular the magnetic field is to the circuit, the more current is induced.

The greater the amount of magnetic field lines (the strong the magnetic field), the greater the current induced. Not surprisingly.

Generators

As we learned before, generators convert mechanical energy into electrical energy.

For example, a hydroelectric plant converts falling water into rotational motion (like using a water wheel).

This rotational motion turns a wire loop in a magnetic field, inducing an emf.

Generators

Generators produce a constantly changing emf, due to the angle between the magnetic field and the wire (circuit) constantly changing.

This is what produces alternating current.

The frequency of rotation of the coil determines the frequency of the sign change of the emf.

Motors

Motors are devices that convert electrical energy to mechanical energy.

Like generators in reverse: A current is run through a wire coil connected to

a rotating shaft. As that wire rotates, it will be alternately

attracted and repelled by any magnet in its vicinity.

Recap

Any relative motion between a magnet and a circuit induces a current in that circuit.

The induced emf is greatest when the magnetic field is perpendicular to the circuit.

Generators convert mechanical energy to rotational motion, rotating a wire coil in a magnetic field.

Motors convert electrical energy to mechanical, using a magnet to repel and attract a wire coil repeatedly.

Homework

Due Friday:

p802 #2

p 821 #5, 15, 16, 22