GRADE: Eighth

CONTENT STANDARD: Physical Science

CONTENT TOPIC: Motion and Forces

CONCEPT: Magnetism is a form of energy because its forces can do work.

CONTENT OBJECTIVES: 81.00 To understand how magnetism exerts force on objects.

INSTRUCTIONAL OBJECTIVES: The learner will:

1.01 define these terms: magnetism, poles, compass, magnetic field, lines of force, electromagnet.
1.02 name two properties shared by all magnets.
1.03 describe how one magnet will affect another.
1.04 explain how electricity and magnetism are related.
1.05 explain how an electromagnet is made.
1.06 describe ways to increase the strength of an electromagnet.
1 .07 list the properties of a magnet's poles and magnetic field.

I. Magnetism
A. How magnetism is produced
B. How magnetism is measured
C. How magnetism is used

TN COMPONENT OF SCIENCE: Process Of Science

TN GOAL:

To enable students to demonstrate the process of science by posing questions and investigating phenomena through language, methods and instruments of science

1.1 OBSERVING - The senses are used to develop an awareness of an event or object and the properties thereof.

1.1a Observing is a process used to develop an awareness of the surrounding environment.

BENCHMARK: By incorporating prior knowledge with the process of observations a better understanding of one's environment may develop.

1.1b The human senses and technological instruments are used to gather information from the environment.

BENCHMARK: Scientific investigation is enhanced through the use of technology.

TIME REQUIRED:

3 to 5 instructional periods

a variety of magnets (bar, horseshoe, etc.), nails, paper clips, steel knitting needles, compasses, small test tubes with coils (or small glass jars with lids), iron filings, iron wire, pliers or wire cutters, 10-inch squares of stiff paper, pencils, string, sewing or darning needles, glass, water, cork, dry cells, lots of copper wire, large iron nails

Compass, electromagnet, lines of force, magnetic field, magnetism, poles

(Have on hand a variety of magnets - different shaped magnets and magnets made of different materials.) Most of you have used magnets many times. You know that a magnet attracts iron and some other metals. Magnets are made of different materials and have different shapes. Some magnets even get their names from their shapes: like this straight magnet (show it) is a bar magnet, and this one (show it) shaped like a horseshoe is called a horseshoe magnet. You also know that magnets have north and south poles and the magnet's force is stronger at the poles. (Demonstrate by using the ends of the bar magnet to pick up nails or paper clips and then try picking up the same objects with the middle of the magnet. Another property that all magnets have is that the same pole always points north. (Have students observe the magnetic needle of a compass.) And you also have observed that the north poles repel each other as do the south poles. (Demonstrate with two bar magnets.) But the north and south poles attract each other (demonstrate). In this lesson we will learn what makes magnets act the way they do and how electricity and magnetism are related.

No one knows exactly what causes magnetism. We do know that it is a form of energy; a force of attraction that a magnet has for iron and certain other metals. The ancient Greeks found that a certain rock, which they called a lodestone, attracted bits of metal to it. Today we know lodestone is a piece of iron ore that is a natural magnet. Since the Greeks found their lodestones near Magnesia in Syria, they called them magnetite from which we get our term magnetism. Scientists have determined that iron, steel, and a few other metals are made up of very small magnetic particles. A magnet can be used to magnetize other pieces of iron (Have students do Activity One under Active Participation.)

The nail, the steel, and the iron filings were all made to act like magnets. When rubbed with the magnet, the particles that made up these objects lined up in a certain way. The north magnetic poles of each particle point in one direction and the south magnetic poles point in the opposite direction. When the particles are all lined up, the nail, the steel, and the iron filings all formed a magnet. When you shook the test tube and disturbed the particles you no longer had a magnet. The iron will soon lose most of its magnetism but the steel will hold its magnetism longer. Try another experiment to help you see that a magnet is made of magnetized parts. (Have students do Activity Two under Active Participation.)

The law of magnets states that like poles repel each other and unlike poles attract each other. We found the same to be true of electric charges. A magnet exerts a force that we cannot see. A force is a push or pull. It is this force that pulls opposite poles of magnets together and pushes like poles apart. (Have students do Activity Three under Active Participation.)

The lines that the iron filings follow are called the lines of force. We can't see the lines of force - they are invisible around the magnet. If we could see them they would show us the strength and direction of the magnet's force. The area around the magnet where the force acts is its magnetic field.

Look at your drawing. The lines follow the lines of force around the magnet. There are lots of lines leaving or entering the ends, or poles, but very few lines are near the center of the magnet. At the beginning of this lesson we tried to pick up objects with the center of a bar magnet. It did not have much pull. This is because the tiny particles in the magnet are all in a line. The north ends of each particle point in the same direction and the south ends point in the opposite direction. The needle of a compass is a magnet. The needle always points approximately north and south. (Have students do Activity Four under Active Participation.)

You found out by these experiments that a compass is simply a magnet suspended so that it is free to turn on a pivot. And when you suspended a bar magnet or floated a magnetized needle they acted exactly as the compass needle. In both cases, the magnets arranged themselves in a north-south position. Some force we cannot see affects the magnets. It makes them take a definite position. This force seems to come from the earth. The earth is like a huge magnet. It has north and south magnetic poles which are strong enough to attract compass needles. A magnetic field surrounds the earth. A compass points in the same direction as the lines of force in the earth's magnetic field. Scientists have found that magnetism and electricity are related. We learned in our study of electricity that magnets can be used to generate electricity. An electric current can also be used to produce magnetism. A wire carrying an electric current has magnetic properties. (Have students do Activity Five under Active Participation.)

The wire carrying the electric current has magnetic properties: it picked up the iron filings and since the iron filings formed circles around the wire you knew there were lines of force around the wire. A single wire does not have very much magnetic force. In order to increase the force you would need to use more wire. Winding a wire in a coil brings all the lines of force closer together. It is like having many wires side by side. In this way it is possible to make a much stronger magnet. (Have student do Activity Six under Active Participation.)

You found that a coil of wire carrying electricity can do all the things a permanent magnet can do. However, an electric wire coiled around an iron core makes a much stronger magnet. We call this kind of magnet an electromagnet. Electromagnets are very useful because their magnetism can be turned on and off. You can also control the strength of an electromagnet while you can't control the magnetic force of a permanent magnet. You increased the strength of your electromagnet by increasing the number of turns of wire in the coil or by increasing the current.

The discovery of the electromagnet is one of the most important man has made. They play a vital role in our lives. They are used in many of our machines. They can be used to produce motion. Electromagnets are used in electric motors which run many of our appliances such as irons, clocks, refrigerators, and dishwashers. Every electric doorbell contains an electromagnet as do our telephones and telegraphs. Electromagnets are used to generate electricity. Most of the electricity we use today is produced by large generators that use powerful electromagnets. A strong electromagnet is also part of a crane. The iron core will pick up magnetic material when the current is on. This makes it possible to lift heavy loads of iron and move them from one place to another. The load can be dumped when the electricity is stopped. Automatic circuit breakers are replacing fuses. In this device, a magnetic coil is used to turn off a switch when too much current flows. The whole electrical industry is dependent on the electromagnet and all its possibilities have not yet been discovered.

1. Magnetizing with magnets:
A. Have students work in groups. Give each group a magnet, a nail, a steel knitting needle, a compass, a small test tube with cork or small jar with lid, paper clips, and iron filings. Rub a nail ten times in the same direction with one end of the magnet. Rub the steel knitting needle the same way. Now see how many paper clips you can pick up with the nail and then with the needle. Which picked up more? (The needle - steel makes a better magnet than iron and holds its magnetism longer).

B. Have students fill the test tube or small jar half full of iron filings. Put the cork or lid on. Hold the glass horizontally. Rub the glass ten times in the same direction with one end of a magnet. Watch the iron filings. Do not jar the test tube. Bring a compass near one end of the test tube. What do you observe? (response) Did the iron filings act like a magnet? (yes) Now shake the glass of iron filings and bring the compass close again. Did the iron filings act like a magnet? (No)

2. Working in small groups have students magnetize a straight piece of iron wire (or you can use a nail but it will be harder to cut). Rub the iron ten times in the same direction with one end of a magnet. Test it to see if you have a weak magnet. Find out which end is north by bringing it near a compass. Now cut the iron in half with pliers or wire cutters. Test each half with the compass. Does each half act the same as the whole piece? (yes) Test each half's magnetism. (Each piece should be a magnet but not as strong as the whole piece.) Why did the iron behave like this? (because all the tiny particles that make up the iron are lined up in the same direction so each piece will be a magnet and each will have a north and south pole.)

3. Working in small groups have students put two bar magnets on a table with the north pole of one about an inch from the south pole of the other. Put a stiff paper (about ten inches square) over the magnets. Sprinkle a thin layer of iron filings on the paper. Tap the paper gently. Do the iron filings arrange themselves in lines? (yes) Now very carefully draw pencil lines along the lines of the iron filings. These lines represent the forces of the magnets. Did your lines go from pole to pole? (Yes - the lines of force went between the two magnets; they seemed to join the two magnets together.) Now repeat the experiment but put the north poles of the magnets about an inch apart. Put another piece of paper over the magnets and sprinkle with iron filings. Very carefully draw pencil lines. Compare your line drawing with the first one you did. How are they different? (The lines of force did not go from pole to pole - the lines from one pole seemed to lead away from the lines from the other pole.) Notice the lines on both drawings that go from the North Pole to the South Pole in each magnet. On the individual magnet where are the lines the fewest? (In the center of the magnet.) What does this mean? (The center of the magnet does not have as much force or pull.)

4. Examine the direction a compass needle points:

A. Working in groups have students hold the north pole of a magnet near the end of the compass needle that points south. What happened? (The north pole of the magnet attracts the south end of the compass needle.) Now hold the north pole of the magnet near the north end of the needle. What happened? (The north pole of the magnet repels the north end of the needle.) Repeat these using the south pole of the magnet. What was the result? (The south pole attracts the north end of the needle and repels the south end.)

B. Tie a piece of string around the center of a bar magnet. Hold the ends of the string by your fingers so that the magnet is suspended and evenly balanced. Put a compass on the table and when the bar magnet is perfectly still check the direction it points with the compass. (The magnet will align itself in a north-south position.)

C. Magnetize a sewing or darning needle by rubbing it with a magnet. Fill a glass with water and float a cork on the water. Carefully lay the magnetized needle across the cork so that it is balanced. When they are still, check the direction the needle is pointing with a compass. (Be sure to keep the compass well away from the needle.)

5. Have students work in small groups. Give each group a dry cell, eight to twelve inches of copper wire, and iron filings. Connect only one end of the wire to the dry cell. Hold the wire near the iron filings. What happened? (Nothing) Now connect the other end of the wire to the dry cell and hold the wire near the iron filings. What happened now? (A wire carrying current picks up iron filings.) Observe how the iron filings act on the wire. (The iron filings form circles around the wire.) Why? (Because there are lines of force around the wire) Disconnect one wire so that the iron filings drop off. Now reconnect it and test the strength of your magnet by seeing how many paper clips or nails it will pick up.

6. Give the students a much longer length of copper wire and a large iron nail. Wind about twenty turns of wire around the nail leaving about the same length sticking out at each end of the nail. Connect these two ends of wire to the dry cell. You now have an electromagnet. Touch one end of the nail to some clips. What happens? Now take one end of the wire off the dry cell and watch your paper clips on the nail. (Electromagnets attract objects only when electricity is running through them.) Next wind forty turns of wire around a nail. Can it pick up more paper clips? (Yes) Now connect this same nail and wire to two dry cells. How many more paper clips can it pick up? (response) In what ways did you increase the strength of your electromagnet? (You increased the number of turns of wire and you increased the amount of electric current.)

Magnets have had a great influence on our civilization. Because of compasses on ships many voyages and discoveries were made possible. Then when we discovered the relationship between magnetism and electricity, we developed the electromagnet. Electromagnets have changed our world, especially in generating electricity which supplies power for our homes, industries, communication, transportation, and many other purposes.

compass - a magnet suspended so that it is free to turn on a pivot

electromagnet - a magnet made by passing an electric current through coils of wire wound around an iron core

lines of force - the imaginary lines around a magnet that represents the strength and direction of the magnetic force

magnetic field - the area around a magnet where its force acts

magnetism - a force of attraction that a magnet has

poles - the place on a magnet where the force is the strongest

resistance - opposition to the flow of electrons

static electricity - electricity that is not moving

turbine - a kind of wheel with blades that are turned by water, air, or steam; it is used to spin the armature inside a generator

volt - unit used to measure the amount of electrical pressure in a circuit; it is measured by an instrument called a voltmeter

watt - unit used to measure the power of an electric current

This is the time this file has been accessed since 04/04/98.

The University of Tennessee at Martin is not responsible for the information or views expressed here.

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