Magnetic and Non-Magnetic Materials

 

A Greek shepherd named Magnes discovered magnets 4,000 years ago in Magnesia, Greece. The name magnetite has been derived from Magnesia or Magnes. Magnets are named after Magnetite.Magnets attract magnetic materials. Natural rocks that have the property of attracting iron are called naturals magnets.These natural magnets have the magnetic property of attracting materials like iron.

 

Activity -1

Let us walk in the footsteps of Magnes . Only, this time, we will change the positions of the magnet and the iron. There will be a magnet at the end of our shepherd's stick. We can attach a small magnet to a hockey stick, walking stick or a cricket wicket with a tape or some glue. Let us now go out on a "Magnes walk" through the school playground. What does our "Magnes stick" pick up from the school ground? What about objects in the classroom?

 

Collect various objects of day-to-day use from your surroundings. Test these with the "Magnes stick". You can also take a magnet, touch these objects with it and observe which objects stick to the magnet. Prepare a table in your notebook as shown in Table.1. and record your observations.

 

Look at the last column of Table.1 and note the objects that are attracted by a magnet. Now, make a list of materials from which these objects are made. Is there any material common in all the objects that were attracted by the magnet?

 

We understand that magnet attracts certain materials where as some do not get attracted towards magnet.

The materials which get attracted towards a magnet are magnetic – for example, iron, nickel or cobalt. The materials which are not attracted towards a magnet are non-magnetic materials.  Examples of non-magnetic materials include rubber, coins, feather and leather.

Is soil a magnetic or a non-magnetic material?

 

Name of the object	Material which the object is made of (Cloth/plastic/ aluminium/ wood/ glass/ iron/ any other	Attracted by Magnes stick/ magnet (Yes/No)
Iron ball	Iron	yes
scale	Plastic	no
Shoe	Leather	?

 

 

Activity - 2

Rub a magnet in the sand or soil. Pull out the magnet. Are there some particles of sand or soil sticking to the magnet? Now, gently shake the magnet to remove the particles of sand or soil. Are some particles still sticking to it? These might be small pieces of iron (iron filings) picked up from the soil.

 

Through such an activity, we can find out whether the soil or sand from a given place contains particles that have iron. Try this activity near your home, school or the places you visit on your holidays.Make a table of what you find. 

 

POLES OF MAGNET

We observed that iron filings (if they are present) stick to a magnet rubbed in the soil. Did you observe anything special about the way they stick to the magnet?

 

Activity - 3

Spread some iron filings on a sheet of paper. Now, place a bar magnet on this sheet. What do you observe? Do the iron filings stick all over the magnet? Do you observe that more iron filings get attracted to some parts of the magnet than others? Remove the iron filings
sticking to the magnet and repeat the activity. Do you observe any change in the pattern with which the iron filings get attracted by different parts of the magnet? You can do this activity using pins or iron nails in place of iron filings and also with magnets of different shapes.

 

Draw a diagram to show the way iron filings stick to the magnet. We find that most of the iron filings are attracted towards the two ends of a bar magnet. These ends are the poles ofthe magnet. Try and bring a few magnets of different shapes to the classroom. Check for the location of the poles on these magnets using iron filings. Can you now mark the location of poles in the kind of magnets?

 

Finding Directions

 

Magnets were known to people from ancient times. Many properties of magnets were also known to them. You might have read many interesting stories about the uses of magnets. One such story is about an emperor in China named Hoang Ti. It is said that he had a chariot with a statue of a lady that could rotate in any direction. It had an extended arm as if it was showing the way . The statue had an interesting property. It would rest in such a position that its extended arm always pointed towards South. By looking at the extended arm of the statue, the Emperor was able to locate directions when he went to new places on hisiot.

 

Let us make such a direction finder for ourselves.

 

Activity - 4

 

Take a bar magnet. Put a mark on one of its ends for identification. Now, tie a thread at the middle of the magnet sohat you may suspend it from a woodenstand (Fig.2). Make sure that the magnet can rotate freely. Let it come to rest. Mark two points on the ground to show the position of the ends of the magnet when it comes to rest. Draw a line joining the two points. This line shows the direction in which the magnet was pointing in its position of rest. Now, rotate the magnet by gently pushing one end in any direction and let it come to rest. Again, mark the position of the two ends in its position of rest. Does the magnet now point in a different direction? Rotate the magnet in other directions and note the final direction in which it comes to rest.

 

                                   Fig.2.

Do you find that the magnet always comes to rest in the same direction? Now can you guess the mystery behind the statue in the Emperor's chariot?

 

Repeat this activity with an iron bar and a plastic or a wooden scale instead of a magnet. Do not use light objects for this activity and avoid doing it where there are currents of air. Do the other materials also always come to rest in the same direction?

 

We find that a freely suspended bar magnet always comes to rest in a particular direction, which is the North- South direction. Use the direction of the rising sun in the morning to find out the rough direction towards east, where you are doing this experiment. If you stand facing east, to your left will be North. Using the Sun for finding directions may not be very exact, but, it will help to make out the direction North from the South, on your line. Using this you can figure out which end of the magnet is pointing to the North and which points to the South.

 

The end of the magnet that points towards North is called its North seeking end or the North pole of the magnet. The other end that points towards the South is called South seeking end or the South pole of the magnet. All magnets have two poles whatever their shape may be.
Usually, north (N) and south (S) poles are marked on the magnets.

 

This property of the magnet is very useful for us. For centuries, travellers have been making use of this property of magnets to find directions. It is said that in olden days, travellers used to find directions by suspending natural magnets with a thread, which they always carried with them.

 

Later on, a device was developed based on this property of magnets. It is known as the compass. A compass is usually a small box with a  glass cover on it. A magnetised needle is pivoted inside the box, which can rotate freely (Fig. 3). The compass also has a dial with directions marked on it. The compass is kept at the place where we wish to know the directions. Its needle indicates the north-south direction when it comes to rest. The compass is then rotated until the north and south marked on the dial are at the two ends of the needle. To identify the north-pole of the magnetic needle, it is usually painted in a different colour.

 

       Fig.3.

 

Activity - 5

Make your own Magnet

There are several methods of making magnets. Let us learn the simplest one. Take a rectangular piece of iron. Place it on the table. Now take a bar magnet and place one of its poles near one edge of the bar of iron. Without lifting the bar magnet, move it along the length of the iron bar till you reach the other end. Now, lift the magnet and bring the pole (the same pole you started with) to the same point of the iron bar from which you began (Fig. 4.). Move the magnet again along the iron bar in the same direction as you did before. Repeat this process about 30-40 times. Bring a pin or some iron filings near the iron bar to check whether it has become a magnet. If not, continue the process for some more time. Remember that the pole ofthe magnet and the direction of its movement should not change. You can also use an iron nail, a needle or a blade and convert them into a magnet.

 

Fig.4.

 

 You now know how to make a magnet. Would you like to make your own compass?

 

Activity - 6

Magnetise an iron needle using a bar magnet. Now, insert the magnetised needle through a small piece of cork or foam. Let the cork float in water in a bowl or a tub. Make sure that the needle does not touch the water . Your compass is now ready to work. Make a note of the direction in which the needle points when the cork is floating. Rotate the cork, with the needle fixed in it, in different directions. Note the direction in which the needle points when the cork begins to float again without rotating. Does the needle always point in the same direction, when the cork stops rotating?

 

Attraction and Repulsion between Magnets

Let us play another interesting game with magnets. Take two small toy cars and label them A and B. Place a bar magnet on top of each car along its length and fix them with rubber bands (Fig.5.)

 

Fig.5.

 

 

In car A, keep the south pole of the magnet towards its front. Place the magnet in opposite direction in car B. Now, place the two cars close to one another . What do you observe? Do the cars remain at their places? Do the cars run away from each other? Do they move towards each other and collide? Record your observations in a table. Now, place the toy cars close to each other such that the rear side of car A faces the front side of car B. Do they moveas before? Note the direction in which the cars move now. Next, place the car A behind car B and note the direction in which they move in each case . Repeat the activity by placing cars with their rear sides facing each other. Record your observations in each case.

 

What do we find from this activity? Do two similar poles attract or repel each other? What about opposite poles — do they attract or repel each other?

 

This property of the magnets can also be observed by suspending a magnet and bringing one by one the poles of another magnet near it.

 

A Few Cautions

Magnets loose their properties if they are heated, hammered or dropped from some height . Also, magnets become weak if they are not stored properly. To keep them safe, bar magnets should be kept in pairs with their unlike poles on the same side. They must be separated by a piece of wood while two pieces of soft iron should be placed across their ends (Fig.6.) .

 

Fig.6.

 

 

For horse-shoe magnet, one should keep a piece of iron across the poles. Keep magnets away from cassettes, mobiles, television, music system, compact disks (CDs) and the computer.

  

Summary

 

1. Magnetite is a natural magnet.
2. Magnet attracts materials like iron, nickel, cobalt. These are called magnetic materials.
3. Materials that are not attracted towards magnet are called non-magnetic.
4. Each magnet has two magnetic poles—North and South.
5. A freely suspended magnet always aligns in N-S direction.
6. Opposite poles of two magnets attract each other whereas similar poles repel one another.