Chapter 8 Magnetism and Its Uses Section 1 Magnetism

Magnetism This refers to the properties and the interactions of magnets

Magnets First found by the Greeks nearly 3,000 years ago Lodestone- naturally occurring magnetic rocks

Magnets Lodestone contains magnetite Magnetite- iron based material First found in Magnesia - hence the name “magnetism”

Magnetic Force This as the magnets move closer together and as the magnets move farther apart

Magnetic Field Exerts a force on other magnetic objects Strongest close to magnet Weaker farther away from magnet p. 225 Fig. 1

Magnetic Poles All magnets have a north and south pole What happens when you break a bar magnet in half?

Destroying a magnet There are only two ways to destroy a magnet: Heat it up Hit it REALLY hard

Magnetic Attraction North and North or South and South poles REPEL each other North and South poles ATTRACT each other

Magnetic Materials Not all metal objects are attracted to a magnet Only those made of materials found in the Iron Triad: Iron, Cobalt, or Nickel

Chapter 8 Magnetism and Its Uses Section 2 Electricity and Magnetism

Electric Current and Magnetism Relationship discovered by Hans Christian Oersted, Danish physics teacher Noticed that flow of electric current affected direction of compass needle

Hypothesized that electric current creates magnetic field He was correct

Look at Figure 8 p. 231 As the direction of the current reverses so does the magnetic field When the current so does the strength of the magnetic field

Electromagnets A temporary magnet Made by wrapping wire around iron core and adding electric current

Magnetic field is stronger in looped wire than straight wire More loops = stronger magnetic field

Solenoid- is a single wire wrapped into a cylindrical wire coil If you have a solenoid wrapped around an iron core you form an electromagnet

Properties of Electromagnets Temporary magnets The strength of the magnetic field can be increased or decreased depending on the # of loops around the iron core

Electromagnets attract magnetic materials and are attracted or repelled by other magnets. They are useful because their magnetic properties can be controlled by changing the current

Electromagnets are used in things like stereo speakers (where they convert electrical energy into mechanical energy to produce sound) and electric motors Fig. 10 p. 233

Electromagnets When the ends are connected: 1. Electrons flow as quickly as possible from the – to the + end of the battery 2. Battery will drain quickly ( there is no load in the middle of the wire) 3.Small magnetic field is produced in the wire

Electromagnetic Devices Galvanometer- devices that use electromagnet to measure electric current Examples: Gauges in your car Electric Motor- a device that converts electrical energy into mechanical energy

Electric Motor Contains an electromagnet The magnetic field flips at the right moment which causes the electric motor to spin freely

Chapter 8 Magnetism and Its Uses Section 3 Producing Electric Current

Moving a loop of wire through magnetic field produces electric current Found by Michael Faraday & Joseph Henry - 1831

Magnet and wire must move relative to each other Causes magnetic field in wire to change over time

That change can induce current in nearby wire Called electromagnetic induction

Generators Uses electromagnetic induction Transforms Mech. Energy  Electrical Energy

Mech. Energy From turning handle This rotates coil of wire between poles of permanent magnet.

Each time end of coil pass poles of permanent magnet the current changes direction. It will change direction twice

Electric Generators Used in cars, and is called an “alternator” Provides electrical energy to operate lights and other accessories

Electricity in Your Home Comes from power plants with huge generators These generators have many a lot of wire wrapped around huge iron cores.

Attached to turbine When fossil fuels burn  heats water  steam pushes turbine blades Used as mech. energy

That mechanical energy turns wire coil Produces electrical energy

Turbines use: Wind Water Steam to turn the blades.

Direct Current “DC” Current flows only in one direction Produced in a battery

Alternating Current “AC” This reverses the direction of the current in a regular pattern Ex: Generator produces AC Wall outlets

Current produced by power plants transmitted along power lines Some current lost as heat Longer the wire, the more current is lost

Reduce Current Loss Transmit current at high voltage 150,000 volts

Transformer Voltage cannot enter home @ 150,000 volts Must be decreased Use transformer

Transformer Used to increase or decrease voltage in AC

Parts of Transformer Primary Coil (comes first) Secondary Coil (comes second) Iron Core

Input vs. Output Voltage Input goes through primary coil Output produced from secondary coil

Step-Up Transformer Increases voltage Secondary coil has more loops than primary coil

Twice as many secondary loops = twice as much output voltage

Step-Down Transformer Decreases voltage Secondary coil has less loops than primary coil

Half as many secondary loops = half as much voltage

Transmitting Alternating Current Step-up transformer used when current leaves power plant Travels through wires Goes through step- down transformer Enters home