When you finish turn to page 224 and begin reading about magnetism.

• When you finish turn to page 224 and begin reading about magnetism

Chapter 8: Magnetism

• Magnetism– Natural Magnets

• Electricity and Magnetism– Electromagnets

• Using and Producing Electricity– Generators and Motors

• Production and Distribution of Electricity– Transformers

• Thousands of years ago, people noticed that a mineral called magnetite attracted other pieces of magnetite and bits of iron.

• They discovered that when they rubbed small pieces of iron with magnetite, the iron began to act like magnetite.

• When these pieces were free to turn, one end pointed north. Lodestone use for navigation.

Early Uses

• Magnets attract objects made of iron or steel, such as nails and paper clips.

• Magnets also can attract or repel other magnets.

Magnets

• Every magnet has two ends, or poles.

• One end is called the north pole and the other is the south pole.

• Two north poles or two south poles repel each other. Like Repel

• North and south magnetic poles are attracted to each other. Unlike Attract

Magnets

• Where the magnetic field lines are close together, the field is strong.

• Field lines that curve toward each other show attraction.

The Magnetic Field

• Field lines that curve away from each other show repulsion.

• A magnet is surrounded by a magnetic field that enables the magnet to exert a magnetic force.

• A moving electric charge creates a magnetic field.

Making Magnetic Fields

• Inside every magnet are moving charges. • All atoms contain

negatively charged particles called electrons.

Making Magnetic Fields

• Not only do these electrons swarm around the nucleus of an atom, they also spin.

• Because of its movement, each electron produces a magnetic field.

Making Magnetic Fields

• A group of atoms, with their fields pointing in the same direction, is called a magnetic domain.

• Normally, these domains are oriented randomly and their magnetic fields cancel each other.

• When a strong magnet is brought near the material, the domains line up, and their magnetic fields add together.

• Microscopic sections of iron and steel act as tiny magnets.

Making Magnetic Fields

• Normally, these domains are oriented randomly and their magnetic fields cancel each other.

• When a strong magnet is brought near the material, the domains line up, and their magnetic fields add together.

Making Magnetic Fields

Earth's Magnetic Field

• The shape of Earth's magnetic field is similar to that of a huge bar magnet tilted about 11º from Earth's geographic north and south poles.

• A compass needle is a small bar magnet with a north and south magnetic pole.

The Compass

• In a magnetic field, a compass needle rotates until it is aligned with the magnetic field line at its location.

• Earth's magnetic field also causes a compass needle to rotate.

The Compass

• The north pole of the compass needle points toward Earth's magnetic pole that is in the north.

• The magnetic pole in the north is actually a magnetic south pole.

• Because of its movement, each electron produces a magnetic field.

Making Magnetic Fields

• A group of atoms, with their fields pointing in the same direction, is called a magnetic domain.

• Normally, these domains are oriented randomly and their magnetic fields cancel each other.

• When a strong magnet is brought near the material, the domains line up, and their magnetic fields add together.

• When a strong magnet is brought near the material, the domains line up, and their magnetic fields add together.

Making Magnetic Fields

Current Can Make a Magnet

• Magnetic fields are produced by moving electric charges.

• When electric current flows in a wire, electric charges move in the wire.

• As a result, a wire that contains an electric current also is surrounded by a magnetic field.

Electromagnets• A current-carrying

wire wrapped around an iron core is called an electromagnet.

• An electric doorbell uses an electromagnet.

• By changing the current, the strength and direction of the magnetic field of an electromagnet can be change.

Using Electromagnets

• The magnetic field of an electromagnet is turned on or off when the electric current is turned on or off.

• By changing the current, the strength and direction of the magnetic field of an electromagnet can be change.

Solenoid and Electromagnets

Wire coils around iron rod

Battery

Iron

Using Electromagnets

• An electric doorbell uses an electromagnet.

Galvanometerpage 234-235

S

N SN S

Current

Magnets Push and Pull Currents

• Current-carrying wires produce a magnetic field.

• This magnetic field behaves the same way as the magnetic field that a magnet produces.

Magnets Push and Pull Currents

• Two current-carrying wires can attract each other as if they were two magnets.

Electric Motor• Magnetic field like

the one shown will push a current-carrying wire upward.

• Any device that converts electric energy into kinetic energy is a motor.

Electric Motor

• To keep a motor running, the current-carrying wire is formed into a loop so the magnetic field can force the wire to spin continually.

Using Magnets to Create Current• If a wire is pulled

through a magnetic field, the electrons in the wire also move downward.

• The magnetic field exerts a force on the moving electrons, causing them to move along the wire.

Using Magnets to Create Current• A device called a generator uses a magnetic

field to turn motion into electricity. • Electric motors and electric generators both

involve conversions between electric energy and kinetic energy.

• In a generator, kinetic energy is changed into electric energy.

• When a wire is made to move through a magnetic field, an electric current is produced in the wire.

• Where the magnetic field lines are close together, the field is strong.

• Field lines that curve toward each other show attraction.

The Magnetic Field

• Field lines that curve away from each other show repulsion.

• When a strong magnet is brought near the material, the domains line up, and their magnetic fields add together.

Making Magnetic Fields

Solenoid and Electromagnets

Wire coils around iron rod

Battery

Iron

Electric Motor• Magnetic field like

the one shown will push a current-carrying wire upward.

• Any device that converts electric energy into kinetic energy is a motor.

Using Magnets to Create Current• If a wire is pulled

through a magnetic field, the electrons in the wire also move downward.

• The magnetic field exerts a force on the moving electrons, causing them to move along the wire.

Electric Generators

• In a generator, an energy source spins a wire loop in a magnetic field.

• Every half turn, the current will reverse direction.

Electric Generators

• This causes the current to alternate from positive to negative.

• Such a current is called an alternating current (AC).

• In the United States, electric current change from positive to negative to positive to positive 60 times each seconds.

Types of Current

• In a direct current (DC) electrons flow in one direction. Wet cells and dry cells produce DC current.

• In an alternating current, electrons change their direction of movement many times each second.

• Some generators are built to produce direct current instead of alternating current.

Power Plants• Electric generators produce almost all of the

electric energy used all over the world. • Different energy sources are used to provide the

kinetic energy to rotate coils of wire in a magnetic field.

• Burning fuels

• Coal, Natural Gas

• Moving Fluid

• hydroelectric, wind turbines

• Nuclear Energy

Power Plants

• Coal-burning power plants are the most common.

• This picture is deceiving.

• Problems

• Dirty to mine

• Dirty to burn

• We will run out

• Global Warming

Making, Distributing,

Using Electrical Energy

Voltage• Voltage is a measure of how much energy

the electric charges in a current are carrying.

• The electric transmission lines transmit electric energy at a high voltage of about 230,000V.

• Device are needed to increase and reduce the voltage.

• Electrical Power is generated at a voltage of about 2,400 Volts.

• Electrical Power is used at a voltage of about 240 Volts

Changing Voltage

• Transformers are used to increase the voltage before transmitting an electric current through the power lines. Step Up Transformer

• Other transformers are used to decrease the voltage to the level needed for home or industrial use. Step Down Transformer

• A transformer is a device that changes the voltage of an alternating current with little loss of energy.

Changing Voltage• A transformer

has two coils of wire wrapped around an iron core.

• One coil is connected to an alternating current source. Primary Secondary

The Transformer Ratio• Whether a

transformer increases or decreases the input voltage depends on the number of coils on each side of the transformer.

22

Primary Secondary

The Transformer Ratio

• In a transformer the voltage is greater on the side with more coils.

• If the number of coils on the input side is less than the number on the output side, the voltage is increased.

• If the number of coils on the input side is more than the number on the output side, the voltage is decreased.

Summary of E&MPrinciple Application

A current moving in a wire produces a magnetic field around the wire

Solenoid, electromagnet, doorbell, door locks, automatic controls

The magnetic field of a permanent magnet will exert a force on the magnetic field around a current carrying wire.

Galvanometer- a device for measuring electric current.Electric motorStereo Speaker

A wire moving through the magnetic field of a permanent magnet will produce an electric current in the wire.

Generator

A changing magnetic field will “induce” a current in a stationary wire.

Transformer

ScheduleDate Activity Assignment

Monday 2/4 Review/Electrical Generators

Tuesday 2/5 Faraday Video

Wednesday 2/6 Magnetism Lab

Thursday 2/7 Transformers and Electrical Distribution

Friday 2/8 Transformer Problems

Monday 2/11 Notetaking worksheet

Tuesday 2/12 Chapter Review

Wednesday 2/13 Chapter 8 Test

Wednesday 2/20 DUKE Energy Field Trip 8:00 – 10:30

Step Up Transformer

Step Down Transformer

Input Output

Step Up/Step Down Transformers

V input

# input coils = V output

# output coils

Electric Power production and distribution

Page 260

Produce Heat60%

Heat to Steam90%

Steam to Rotation

75%

Rotation to Electricity

95%

Step Up Transformer

High Voltage wires

Step Down

Transformer

Distribution Lines

Step Down Transformer

Household

Usage

Connecting Electricity and Magnetism

• Electric charges and magnets are related to each other.

• Moving electric charges produce magnetic field.

• A moving magnetic field make electric charges move.

Definitions 1

• Solenoid – a coil of wire carrying an electric current which produces a magnetic field.

• Electromagnet- a coil of wire (solenoid) with an iron core which produces a stronger magnetic field.

• Applications – doorbells, actuators of all sorts

Definition 2• Galvanometer- a device for measuring

electrical current. Also called an ampmeter.• Electric motor- a device that uses a

electromagnet in the field of a permanent magnet to produce rotational motion.

• A (DC) electric motor requires a commutator to interrupt and change the direction of the electric current

Definition 3• Electric generator – a device that changes the

motion of a coil rotating in the field of a permanent magnet to produce an electric current.

• The current produced by a generator changes direction twice in each revolution of the coil. The current produced by a generator is called Alternating Current.

• With modifications a generator can produce direct current.

Definition 4

• Transformer- a device that changes the voltage of electric current.

• Primary coil – the coil through which the input current flows.

• Secondary coil – the coil through which the output current is produced.

• Core – the iron around which both the input coil and the output coil are wound.

Example (Page 244)Assignment- Applying Math 6If the input voltage is 120 volts and the primary coil (input) has 100 turns, what will the output voltage be if there are 10 turns on the secondary (output) coil?

V input

# input coils = V output

# output coils

120V 100

V output

10=