Why a magnet?

More than 2,000 years ago, a type of rock was discovered in a region known as Magnesia in what is modern-day Turkey that attracted iron. The Greek philosopher Thales of Miletus was the first to refer to this substance when writing in the seventh century BC. The rock was named magnetite from which comes the word 'magnet'. It is also called lodestone.

 

Lodestone

 

Also in ancient times, the Chinese used this stone to help them find their way (see Figure 1). When tied to a piece of string, the stone always pointed in the same direction. The name lodestone really means leading stone.

 

Magnets

Magnets come in a variety of shapes.

Horseshoe magnet

Horseshoe magnet

Round magnet

 

What will a magnet do?

 

 

The magnet in this picture is attracting nails. They are 'sticking' to one of its ends. Will a magnet act in the same way on anything? Use a magnet to experiment to find out.

 

Place a lot of different things in a box and try each one with your magnet to see if the magnet will attract to one of its ends. Make a list of what the magnet will and will not attract.

 

Put these on your list: rubber, wood, a plastic comb, a needle, wool, a knife, a nail, a brass screw, different coins, a pin, a marble, a button, and a piece of glass.

 

How to do this experiment

 

 

In your last experiment you have discovered that a magnet only attracts things with iron in them. Now do this experiment.

 

Put a pin or a small nail on a desk lid or a table top. Put your magnet underneath. Will your magnet attract the pin? Does the wooden top stop the magnet from attracting the pin?

 

Try this experiment again with other things between the magnet and the pin or nail. Try a sheet of paper, a sheet of rubber, a sheet of plastic, and a sheet or cardboard. Try a sheet of glass.

 

A game to play

 

 

Cut out a soccer player as shown and paste onto a piece of stiff white card. Cut out carefully. Make several of these soccer players.

 

You will need several corks. Cut a slot across each cork and fix in a soccer player. Use a little glue. Into the bottom of each cork stick a large steel-headed drawing pin (thumb tack). Fix strong magnets to the end of a ruler or a piece of wood (see Figure 2).

 

 

Mark a small soccer pitch on a piece of hardboard or a piece of glass. Put the layers on the pitch and move them from underneath the board by using the magnets. The magnet will attract the steel-headed drawing pin and move the players. Use a ping-pong ball for the soccer ball.

 

The ends of a magnet

 

 

A magnet has two ends which are called POLES. One is called a NORTH POLE and the other a SOUTH POLE. The north pole of a magnet is marked with the letter 'N' (see Figure 3). A round magnet is not marked with an 'N' but sometimes has a spot to show the north pole.

 

The poles of a magnet look the same but they do not behave in the same way.

 

Try this experiment

Take two bar magnets and place them on a table. Carefully bring the north poles together. What happens? Do the experiment once more. The magnets push each other away (see Figure 4).

 

Now try the north pole of one magnet and the south pole of the other magnet. This time the magnets 'stick' together (see Figure 5). Try this experiment several times to learn what happens.

 

There is a very simple rule to help you remember what happens to the poles of a magnet. When the 'same' poles are placed together, they push away. When 'opposite' poles are placed together they attract.

 

The rule is this (see Figure 6):
LIKE POLES REPEL
UNLIKE POLES ATTRACT

 

A compass

 

 

A compass is used to show direction. The needle of a compass always points in the same direction. Lodestones, which are magnetic, were also used to show direction.

 

Is the needle of a compass magnetic?

 

Do this experiment to find out.

 

Point the north pole of your magnet to the compass needle. What happens? Point the south pole of your magnet to the compass needle. What happens this time?

 

Remember the rule: LIKE POLES REPEL, UNLIKE POLES ATTRACT. What happened to the needle of the compass?

 

When the magnet was pointed to the compass needle, the needle was made to move (see Figure 7). One end of the compass needle was attracted to the pole of the magnet. When the other pole of the magnet was pointed to the compass needle, the other end of the needle was attracted (see Figure 8).

 

This tells you a very important fact. A compass needle is really a very small magnet. Can you use a bar magnet as a compass?

 

Do this experiment

Cut a piece of paper and fold round a bar magnet. Place a piece of cotton through the ends of the paper. Make sure that the bar magnet is level. Tie the cotton to something which will let the magnet swing (see Figure 9).

 

After a time the magnet will stop swinging and you will notice that the north pole is pointing in the same direction as the compass needle. The magnet is now a compass needle.

 

Now experiment again

Place the north pole of another magnet to the north pole of the compass needle you have made. What happens? The poles repel each other (see Figure 10).

 

Put the south pole of the magnet to the north pole of the compass needle you have made. What happens this time? The poles attract each other (see Figure 11).

 

Do south poles repel each other?

 

How to make a magnet

You can make a magnet very easily. Do this experiment. You will need a large steel needle and a magnet (see Figure 12).

 

Hold the needle flat and stroke the magnet's north pole along the needle from the eye to the tip. Do this 12 times, as you see in the picture. Always stroke in the same direction. When you have done this take the needle and experiment with a compass.

 

Point the eye of the needle to the north pole of the compass. What happens? (see Figure 13)

 

Point the tip of the needle to the north pole of the compass. What happens now (see Figure 14)?

 

Can you say what has happened? You have made a magnet.

 

From your experiment can you tell which end of the needle is the north pole? Remember the rule for magnets.

 

Now do this

Earlier you saw how to make a magnet into a compass needle. Do the same thing with the needle you have just magnetized.

 

Now hang the needle somewhere and experiment with your magnet to show that the rule for magnets is true (see Figure 15).

 

Now do this experiment

You have already seen how to magnetize a needle. What happens if you use the south pole of the magnet to stroke along the needle? Do this experiment and see what happens.

 

If you have a box of unmarked magnets and a compass, how could you tell which ends of the magnets are north poles?

 

Make this compass

Print this compass dial, cut it out, stick it into the bottom of a piece of card, and cut the card to the same shape (see Figure 16).

 

Stick a pin through a piece of cork (see Figure 17).

 

Magnetize a large needle as described earlier.

 

Use half of a pres stud and fix the needle to it by using a little piece of plasticine.

 

Balance the needle on the pin in the cork. Stick the cork in the middle of the compass dial (see Figure 18).

 

Find out all you can about the compass. Learn how to read it. Learn the compass points. There are more points to learn than north, south, east, and west (see Figure 19).

 

More ways to make a compass needle

 

 

Use plasticine to fix a needle onto a small test tube.

 

Another needle passed through a cork will allow the compass to turn easily.

 

Fix a needle to a ping-pong ball. Fix a small weight to the bottom of the ball. Float the ball in a basin of water (see Figure 20).

 

Magnetic fields

Take some iron filings, a sheet of white A4 paper, and a bar magnet. Now place the paper over the magnet, like this (see Figure 21).

 

Carefully sprinkle some iron filings over the paper (see Figure 22). What can you see?

 

Gently tap the paper with your finger. See the pattern become clearer (see Figure 23). It is the pattern of the bar magnet's magnetic field (see Figure 24).

 

Now do the same with a horseshoe magnet (see Figure 25).

 

Lines of magnetic force

The patterns made by the iron filings shows the force of a magnet. The lines you see are called 'lines of force'.

 

You can now do more experiments with magnets and iron filings to investigate these lines of force.

 

Place the north poles of two bar magnets as shown in Figure 26.

 

Cover the two magnets with a sheet of white paper.

 

This is the picture you will have. You can really see how the lines of force repel (see Figure 27).

 

Now do the experiment again with the north and south poles. This is the picture you will have. This time the lines of force are attracting (see Figure 28).

 

More magnetic field patterns for you to try are shown in Figure 29).

 

Magnetic field pictures you can keep

Here is a way to make these pictures so that you can keep them. Instead of using white paper to make the field patterns, take a piece of waxed paper. Cover the magnet with a piece of this waxed paper make a magnetic field picture. Now carefully lift the waxed paper off the magnet. Do not shake or knock the pattern.

 

Hold the waxed paper over a candle flame, but too close. The heat from the candle will melt the wax on the paper and the iron filings will stick to the wax. When you have finished heating all the waxed paper you will have a magnetic field pattern you can keep (see Figure 30).

 

Make pictures like this of all your experiments with magnetic fields.

 

Make a magnet

 

 

Here is an interesting way to make a magnet. To make this magnet you need an iron bar (or an iron poker) and a hammer. You can use the compass you made to help with this experiment.

 

First, put each end of the iron bar in turn near your compass. The compass needle will move, of course, because the needle is a magnet.

 

Remember the rule for magnets: if the iron bar is a magnet it will repel and attract the compass needle. Do this carefully and make sure the iron bar is not a magnet.

 

Point the iron bar or poker towards the north. Use your compass. Now use the hammer to hit the end of the bar several times. When you test the iron bar again your compass will tell you that it is now a magnet.

 

Earth has a magnetic field

Earth has a magnetic field as shown in Figure 31. This tells you how a compass is able to work. This is why you were able to make an iron bar into a magnet when you used the hammer. Earth's magnetic field magnetized the bar.

 

A magnet can be destroyed

You have seen how a magnet can be made. If you still have a magnetized needle you can use it for this little experiment. If not, you must magnetize another needle. Test your magnetized needle with a compass.

 

Now do this: place the needle in a flame. Hold the magnetized needle in the flame of a methylated spirit lamp. Heat the needle from end to end (see Figure 32). What happens?

 

The needle is no longer a magnet because the heat has destroyed the magnetism.

 

Make a magnet with iron filings

Fill a glass test tube with iron filings. Fix a cork into the end of the test tube.

 

Hold the test tube on the desk or table top and carefully stroke a magnet along the tube to magnetize the iron filings. When you have stroked the test tube several times, repeat the test with the compass to check that the filings have been magnetized (see Figure 33).

 

Now hold the test tube in a flame and heat the iron filings. Test again with the compass and find out if the filings are still magnetized. You will find that the magnetized iron filings have been demagnetized by the heat (see Figure 34).

 

Now use the tube of iron filings for another experiment. Use a magnet to magnetize the iron filings again. Use the compass to test for magnetism. When you have done this give the test tube magnet a good shake. Do this several times and then test with the compass. What has happened this time? Are the iron filings still magnetized?

 

Equal magnetic fields

Place two bar magnets about thre feet (one meter) apart with their north poles facing each other. Now use a compass and experiment with it to find the middle position where the two magnetic fields are equal.

 

This need not be halfway. Try this again with south poles facing each other. Try again with large and small magnets. Use your ruler to measure each experiment.

 

Electromagnets

Electricity can be used to make a magnet. Here is an experiment you can carry out to make an ELECTROMAGNET. You will need a large nail, about 10 centimeters long (se Figure 35).

 

You will also need a battery.

 

Finally you will need some insulated copper wire the thickness of a pin. Clean the ends of the wire carefully and wind 200 turns on the nail.

 

Put the ends of the copper wire to the battery and you will have an electromagnet (see Figure 36). How much will it lift?

 

Make a picture of the magnetic field of an electromagnet using iron filings (see Figure 37).

 

Test the poles of an electromagnet

Is the rule for magnets the same for electromagnets? Hang a magnet like the experiment described earlier and use it to test your electromagnetic nail.

 

Join one end of the wire to the battery and hold the nail close to one end of the bar magnet. Put the other end of the wire to the other side of the battery. What happens?

 

Which end of your electromagnet will repel the north pole of the bar magnet? When you have done this experiment change over the wires on the battery and do it again. What happens now?

 

You will have found that when the wires of the electromagnet are changed over, the poles of the magnet are also changed.

 

This is what to do to be sure which end of an electromagnet is going to be a north pole or a south pole.

 

Wind a nail with wire as shown in Figure 38.

 

If you wind the wire on an electromagnet as shown above and connect the ends of the wires to the battery, the head of the nail will be a north pole.

 

Wind a nail with wire to make an electromagnet but wind the wire as shown in Figure 39.

 

This time the head of the nail will be a south pole.

 

A compass and battery experiment

Put a compass on the desk or table top. Put a length of copper wire across the compass from north to south, as shown in Figure 40.

 

Touch the ends of the wire to the battery connections and use your eyes. What happens to the compass needle? Which way does it move?

 

Electricity from the battery makes a magnetic field around the wire and the compass needle is turned.

 

Turn the battery around and try this experiment again. Which way does the compass needle turn this time? Can you say why the compass needle turned?

 

Michael Faraday

Michael Faraday was a clever scientist who discovered many important things about magnets and magnetism (see Figure 41). It was Faraday who first discovered that magnetism could be used to make electricity.

 

You can try a simple experiment yourself to show what Faraday discovered.

 

Wind 50 turns of insulated copper wire around a matchbox. Take the coil of wire off the matchbox. Put sellotape around as you see in Figure 42. Make two of these.

 

Join the two coils together with long lengths of wire. Fix a small compass inside one coil with the coil facing north and south.

 

Hold a bar magnet in one hand and quickly push it in and out of the other coil (see Figure 43). Experiment with both ends of the magnet. See what happens to the compass needle.

 

In an earlier experiment, electricity from the battery made a magnetic field around the wire and the compass needle was turned. In this experiment with the two coils and the magnet, the magnetic field of the bar magnet makes electricity in the coil of wire. This electricity flows through the wires and makes a magnetic field in the other coil of wire – you can see the compass needle move.

 

Do this experiment again but use an electromagnet inside the coil.

 

Another experiment with electromagnetism

Take a very long nail and wind two coils of wire onto it. Fix your experiment like this as shown in Figure 44.

 

When the battery is connected to the coil the nail becomes an electromagnet. The magnetism from the nail makes electricity flow through the second coil. Watch the compass needle move. See what happens when you connect the battery the other way. You have made a very simple TRANSFORMER.

 

Now make this

Take a 10-centimeter nail. Cut two circles of cardboard and fix them across the nail. Wind on 100 turns of insulated wire the thickness of two pins (see Figure 45).

 

Here is a very long job for you. On top of the first coil you must wind 2,000 turns of very thin wire (see Figure 46). When you have done this connect the first coil wires to a battery.

 

Get a friend to hold the ends of the wires of the second coil. Watch his face. You have made a 'shocking' coil (see Figure 47).

 

Make a magnetic toy

Copy the face outline in Fugure 48 into a shoebox lid.

 

Fix a small magnet to the end of a piece of wood.

 

Put some iron filings in the corner of the box lid and use the magnet under the lid to take iron filings to make hair on the face (see Figure 49).