Notes and ReviewSome is old and some is new

Pay attention and pass the test

Sit in your assigned seats

Shape of Magnetic Fields

• There are two poles, North and South.• They are connected by magnetic field lines

Attraction and Repulsion• Like electric charges, opposites attract and

similar repels (pushes away)

The poles of two magnets that are different or opposite will attract. Magnetic lines of force from north and south poles pull together and join. ...out of north end and into south end...

The poles of two magnets that are the same will repel or push each other apart. ...out of both north ends - repelling or pushing each other apart...

Strength of Magnetic Fields• Where the field lines are drawn close together, the

field is stronger. Thus magnets are stronger at the poles.

Electricity in a coilElectromagnets are made of coils of wire with electricity passing through them. Moving charges create magnetic fields, so when the coils of wire in an electromagnet have an electric current passing through them, the coils behave like a magnet. When the electricity stops flowing, the coils don’t act like a magnet anymore.

Uses of Electromagnets

• Anywhere you need a magnet you can turn on and off

• An electric motor• A speaker

Strength of Electromagnets

What makes an electromagnet stronger? Think about what makes an electromagnet?1. A coil of wire – so add more coils2. An electric current – add more current3. An Iron Core

Magnets and coils of wire • Passing a magnet by a wire generates

________________, which is the principle of a _________________.

1. A bigger coil increases the electricity2. A bigger magnet increases the electricity3. An Iron core increases the electricity4. THE MAGNET (OR COIL) MUST MOVE – The

magnetic field moving in the wire makes the current

ElectricityGenerator

Types of Electric Current

When the voltage switches between positive (+) and negative (-), this is called ______________________, or ____. If the voltage is constant, as with a battery, this is called _______________________, or ____.

Alternating Current AC

Direct Current DC

What can we do with magnets

• When a coil is placed in a magnet and rotated, this produces electricity from mechanical energy. This is called a __________________.

• When electromagnets are placed with magnets to convert electricity into mechanical energy, we have created a ____________________.

Generator

Electric Motor

More Motors

To cause the rotor to turn in a counter-clockwise direction, the north pole of an electromagnet should be placed at position:

The Electromagnet’s North must push (repel) a North on the rotor and/or pull (attract) a south on the rotor

This happens at “A”

Diagram of a transformer

A transformer is composed of 3 things1) An iron core2) A primary coil (NP turns)

3) A secondary coil (NS turns)

What happens in a transformer

When the turns in the secondary coil go up, the voltage _________________. This is called a ___________ transformer. When the voltage in the secondary coil goes up, the current must go _______________, because ________________________________________________________.

increases“step-up”

downTransformers can not increase energy, because of the Law of Conservation of Energy.

Calculations for TransformersIf the ratios are always the same, then we can set them equal to each other, like this:

In other words the ratio of turns is equal to the ratio of voltages.

P

S

P

S

VV

NN