Electricity, Sound and Light

2. Electricity, Sound and Light

3. Chapter Eight: Electricity and Magnetism • 8.1 Electricity • 8.2 Electrical Circuits and Electrical Power • 8.3 Properties of Magnets

4. Investigation 8B Magnetism • What are the properties of magnets?

5. 8.3 Properties of Magnets • If a material is magnetic, it has the ability to exert forces on magnets or other magnetic materials. • A magnetis a material that can create magnetic effects by itself. Which of these is a permanent magnet?

8. 8.3 The magnetic field • A magnet fills the space around itself with a kind of potential energy called the magnetic field. • You can see the pattern of the magnetic field by sprinkling iron filings on cardboard then placing a magnet underneath.

9. 8.3 The magnetic field • The force from a magnet gets weaker as it gets farther away. • Separating a pair of magnets by twice the distance reduces the force by 8 times or more.

11. 8.3 How does a compass work? • A compass needle is a magnet that is free to spin. • The north pole of a compass needle always points toward the south pole of a permanent magnet.

12. 8.3 How does a compass work? • The planet Earth has a magnetic field that comes from the core of the planet itself.

13. 8.3 How does a compass work? • When you use a compass, the north-pointing end of the needle points toward a spot near (but not exactly at) Earth’s geographic north pole. • The south magnetic poleof the planet is near the geographic North Pole.

15. 8.3 The effect of current on a magnet • In 1819, Hans Christian Øersted placed a compass needle near a wire in a circuit. • When a switch in the circuit was closed, the compass needle moved just as if the wire were a magnet.

16. 8.3 Magnetic forces and electric current • A magnet made with wires and electric current is called an electromagnet. • The electromagnet produces a magnetic field exactly the same as a permanent magnet with its north and south poles.

17. 8.3 The right hand rule • When the fingers of your right hand curl in the direction of current, your thumb points toward the electromagnet’s north pole. • You can switch the north and south poles of an electromagnet by reversing the direction of the current in the coil.

18. 8.3 Magnetic forces and electric current • The metals iron, nickel, and cobalt have strong magnetic properties. • Both permanent magnets and iron owe their magnetic properties to their atoms. • Iron atoms can easily rotate their magnetic poles to line up with neighboring atoms.

19. 8.3 Electric generators and induction • The process of using a moving magnet to create electric current or voltage is called electromagnetic induction. • A moving magnet induces electric current to flow in a circuit. • The word “induce” means “to cause to happen.”

21. 8.3 Transformers • A transformer changes the high voltage from the main power lines to the 120 volts your appliances use.

22. 8.3 Transformers • Inside a transformer, the input is connected to the primary coil. • The output of the transformer is connected to the secondary coil. • The two coils have different numbers of turns to convert from one voltage to another.

24. 8.3 Alternating current • Your house uses alternating current or AC at either 120 or 220 volts. • AC voltage reverses direction 60 times per second.

25. Technology Connection Household Electricity • You use electric current every day. • When you plug in an electric appliance, you connect it to a circuit created by wires in the walls.

26. Activity Make a Simple Motor • Electricity and magnetism are two forms of the same basic force. • You will use this idea to create a small motor.