Notes and Review Some 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 coil Electromagnets 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 coils 2.An electric current – add more current 3.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 electricity 2.A bigger magnet increases the electricity 3.An Iron core increases the electricity 4.THE MAGNET (OR COIL) MUST MOVE – The magnetic field moving in the wire makes the current Electricity Generator

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 CurrentAC 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 things 1)An iron core 2)A primary coil (N P turns) 3)A secondary coil (N S 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” down Transformers can not increase energy, because of the Law of Conservation of Energy.

Calculations for Transformers If 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.