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

Chapter 8: Magnetism Magnetism Electricity and Magnetism Natural Magnets Electricity and Magnetism Electromagnets Using and Producing Electricity Generators and Motors Production and Distribution of Electricity Transformers

Early Uses 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.

Magnets Magnets attract objects made of iron or steel, such as nails and paper clips. Magnets also can attract or repel other magnets. Every magnet has two ends, or poles. One end is called the north pole and the other is the south pole.

Magnets Two north poles or two south poles repel each other. Like Repel North and south magnetic poles are attracted to each other. Unlike Attract

The Magnetic Field Where the magnetic field lines are close together, the field is strong. Field lines that curve toward each other show attraction. Field lines that curve away from each other show repulsion.

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

Making Magnetic Fields Because of its movement, each electron produces a magnetic field. 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.

Making Magnetic Fields Microscopic sections of iron and steel act as tiny magnets. Normally, these domains are oriented randomly and their magnetic fields cancel each other.

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

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.

The Compass A compass needle is a small bar magnet with a north and south magnetic pole. In a magnetic field, a compass needle rotates until it is aligned with the magnetic field line at its location.

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

Making Magnetic Fields Because of its movement, each electron produces a magnetic field. 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.

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

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 Iron Battery

Using Electromagnets An electric doorbell uses an electromagnet.

Galvanometer page 234-235 N N S S 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. When a wire is made to move through a magnetic field, an electric current is produced in the wire. In a generator, kinetic energy is changed into electric energy.

The Magnetic Field Where the magnetic field lines are close together, the field is strong. Field lines that curve toward each other show attraction. Field lines that curve away from each other show repulsion.

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

Solenoid and Electromagnets Wire coils around iron rod Iron Battery

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. Electrical Power is generated at a voltage of about 2,400 Volts. Electrical Power is used at a voltage of about 240 Volts The electric transmission lines transmit electric energy at a high voltage of about 230,000V. Device are needed to increase and reduce the voltage.

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

Changing Voltage A transformer has two coils of wire wrapped around an iron core. One coil is connected to an alternating current source. Secondary Primary

2 The Transformer Ratio Whether a transformer increases or decreases the input voltage depends on the number of coils on each side of the transformer. Secondary Primary

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&M Principle 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 motor Stereo 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

Schedule Date 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 Output Input

Step Up/Step Down Transformers V input # input coils V output # output coils =

Electric Power production and distribution Page 260 Produce Heat 60% Steam to Rotation 75% Heat to Steam 90% 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 6 If 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 = V output 10 120V 100 =