Magnetism

Class 6 | Science — Physics | Unit 1

Class 6 Unit 1 Science

Unit 1. Magnetism

Learning Objectives

• To know about the discovery of magnets
• To identify Magnetic and Non Magnetic Materials
• To distinguish between north and south poles
• To list out the properties of magnets
• To explain the principle of Maglev train

Introduction

You might have seen magnets. Have you ever enjoyed playing with them? Take a steel glass with a small magnet in it. Take a needle through which thread is passed. Press the thread with a finger near the hole of the needle as shown in the figure and raise the glass upward slowly.What happens?

Observe the same activity performed by your teacher and note it.

Does the needle stand vertically up without touching the glass? Why does this happen?

1.1 Discovery of Magnets

Magic Stone of Magnus

People wondered about this incident, each and every one expressed their views. What might be the reason for the stick, to get stuck on the rock?

Yes, you are right. That is a magnetic rock. People found it attractive not only for the stick of Magnus, but also for all the materials made of iron. The more rocks of these kinds were found worldwide. These magnetic rocks were named 'Magnets' and the ore is called 'Magnetite' after the name of the boy Magnus. The name is also supposed to come after the name of the place (Magnesia) in which it was found. Magnetite the ore with attracting property found in that region. Magnetite are natural magnets. They are called magnetic stones. Natural magnets do not have a definite shape since they are used for finding direction, they are also called 'leading stones' or 'lode stones.

1.2 Magnet of Different Shapes

After learning the method of changing the piece of iron into magnet (magnetization) we have been making and using several kinds of magnets. Such man-made magnets are called artificial magnets. Bar magnets, Horseshoe magnet, Ring magnet and Needle magnet are generally used artificial magnets. Oval shape, Disc Shapes and Cylindrical magnets are also available.

Activity 1

Take a magnet. Take the magnet closer to the objects surrounding you. What happens? Observe and note.

The objects attracted by the magnet:

The objects not attracted by the magnet:

Which substances are used to make the objects attracted by the magnet?

1.3 Magnetic and Non-Magnetic Materials

Substances which are attracted by magnets are called magnetic substances. Iron, cobalt, nickel are magnetic substances. Substances which are not attracted by magnets are called non-magnetic substances. Paper, plastic are called non-magnetic substances.

1.4 Magnetic Poles

Place some iron filings on a paper. Place a bar magnet horizontally in the filings and turn it over a few times. Now lift the magnet. What do you see?

Which part of the magnet has more iron filings sticking to it?

Which part of the magnet has almost no fillings sticking to it?

The parts of the magnet those attract the largest amount of iron fillings are called as its poles. The attractive force of the magnet is very large near the two ends. These two ends are called its poles. If you have a horseshoe magnet, or any other type of magnet at home, find the position of its poles by this experiment. In experiments with magnets you will need to use iron filings again and again. You can do this by placing a magnet in a pile of sand and turning it around in the sand. The small pieces of iron present in the sand will stick to the magnet. If you cannot find sand you can look for iron pieces in clayey soil as well. If you don't have iron filings, you can collect small pieces of iron and they will serve the purpose as well.

1.5 Finding directions with a magnet

Tie a piece of thread to the centre of a bar magnet and suspend it. Note, in which direction the magnet stops. Draw a line on a sheet of cardboard or the table along the direction in which the bar magnet stops that means a line parallel to the bar magnet. Turn the magnet gently and let it come to a stop again repeated three or four times.

Does the bar magnet stop in the same direction each time?

In which direction does the magnet stop every time?

This is roughly the north-south direction. The end of the magnet that points to the north is called the North Pole, the end of the point to the South is called the south pole. A freely suspended magnet always comes to the rest in a north south direction.

Do You Know?

The directive property of magnets has been used for centuries to find directions. Around 800 years ago, the Chinese discovered that a suspended lode stone stops in the north-south direction. Chinese used these lode stones to find directions. The navigators of that country used to keep a piece of lode stone suspended in their boats and during a storm or mist, they used the lode stone to locate directions.

1.6 Magnetic compass

A Compass is an instrument which is used to find directions. It mostly used in ships and airplane. As a rule, mountaineers also carry a compass with them so that they do not lose their way in unknown places. The compass has a magnetic needle that can rotate easily. The Marked end of the needle is the north pole of the magnet. Can you use a magnetic compass to find the West direction? Ask your teacher to help you in using a magnetic compass.

1.7 Properties of magnets.

Attraction or repulsion

Take two similar magnets place them in four different ways as shown in figure What do you observe?

When do the magnets attract each other?

When do the magnets repel each other?

Unlike poles (S-N, N-S) attract each other. Like poles (N-N, S-S) repel each other.

Activity 2: LET US MAKE MAGNETS

Take a nail or a piece of iron and place it on a table. Now take a bar magnet and place one of its poles near one edge of the nail or piece of iron and rub from one into another end without changing the direction of the pole of a magnet. Repeat the process for 30 to 40 times. Bring a pin or of some Iron fillings near the nail or piece of iron to check whether it has become a magnet. Does the nail or piece of iron attract the pin or fillings? if not continue the same process for some more time.

1.8 Do magnets lose their properties? When?

Magnets lose their properties if they are heated or dropped from a height or hit with a hammer.

Do You Know?

Magnets lose their properties when they are placed near cellphone, computer, DVDs. These objects will also get affected by magnetic field.

Activity 3: Make your own magnetic compass

Insert a magnetized needle, that you made in the activity 2, into two Styrofoam balls (Thermocol balls) and place the needle in the bowl of water. Test whether the floating needle always turned in rest in the north - south direction.

Note: If you don't have Styrofoam balls you can use dry leaf or a cork piece.

1.9 Storage of Magnets

Improper storage can also cause magnets to lose their properties 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 and two pieces of soft iron should be placed across their ends. For a horseshoe magnet a single piece of soft iron can be used as a magnetic keeper across the poles.

1.10 Usage of Magnets.

We use various equipment with magnets in day to day life. Discuss with your friends about the usage of the magnets in the following instances.

1.11 Science Today - Bullet Trains

We know that like poles of a magnet repel each other. Keep two bar magnets as shown in the figure. What do you observe?

By using repulsion, we can levitate a magnetic object. Let us make a toy and enjoy magnetic levitation.

Levitating propeller

place the propeller on the stiff straw. Their magnets in the straw and the propeller should repel each other. This will make the propeller levitate. On placing it under a ceiling fan the propeller will spin very fast. Have you enjoyed with this toy?

Electromagnetic train is working in the same principle. Have you heard about it? Electromagnetic train is called as suspension train and also called as flying train. It does not require diesel or petrol. This technology uses the property of magnetic attraction and repulsion to run these super-fast electromagnetic trains.

How does the electromagnetic train work?

Electromagnets are used in electromagnetic train electromagnets are magnetized only when current flows through them. When the direction of current is changed the poles of the electromagnets are also changed. Like poles of the magnet which are attached at the bottom of the train and rail track repel each other. So, that rain is lifted from the track up to a height of 10 centimetre. We Know that we can move any magnetic object with the force of attraction or repulsion properties of magnets. This train also moves with the help of the magnets attached on the sides of track and the magnets fitted at the bottom side of the train. By controlling the current we can control the magnets and movement of the train. As there are no moving parts, there is no friction. So, the train can easily attain a speed of 300 km per hour. These trains are capable of running up to 600 km/ hour. They do not make any noise. They require less energy and they are eco-friendly. Many countries have taken efforts to use these trains, such trains are used for public transport only in China, Japan and South Korea. In India the possibilities of introducing these trains are under consideration.

Write the difference between a normal and an electromagnetic train.

Points to remember

• Magnetites are natural magnets. They are called magnetic stones.
• Man-made magnets are called artificial magnets.
• Substances which are attracted by magnet are called as magnetic substances
• Substances which are not attracted by magnets are called non-magnetic substances.
• A freely suspended magnet always comes to rest in a north-south direction.
• The end of the magnet that points to the north is called the North Pole.
• The end that points to the south is called the South Pole.
• A compass is an instrument which is used to find directions.
• Like Poles (N-N, S-S) repel each other and unlike poles (N-S, S-N) attract each other.
• Magnets lose their properties if they are heated or dropped from a height or hit with a hammer.

I C T Corner

Magnet

Through this activity you'll be able to understand the properties of magnetic poles and magnetic field lines.

Step 1: Type the URL given or scan the QR code to launch the activity page.

Step 2: A diagram of a bar magnet and a magnetic needle are there. Click and drag the magnetic needle with the use of mouse, around the bar magnet. Observe the position of the magnetic field lines and how the needle rotates according the poles.

Step 3: Click the 'Next navigation icon'. A grid of magnetic needles around a bar magnet will appear. Click and drag the bar magnet. Observe the changes of the needles.

Step 4: Click the 'field lines' check box at the bottom of the activity window to see the magnetic field lines.

Magnet URL: http://www.physics-chemistry-interactive-flash-animation.com/ electricity_electromagnetism_interactive/bar_magnet_magnetic_ field_lines.htm

Evaluation

Exercise 1. Choose the appropriate answer

1. An object that is attracted by a magnet.

a. Wooden piece b. Plain pins c. Eraser d. A piece of paper

2. People who made mariner's compass for the first time.

a. Indians b. Europeans c. Chinese d. Egyptians

3. A freely suspended magnet always comes to rest in the direction

a. North-east b. South-west c. East-west d. North-south

4. Magnets lose their properties when they are

a. Used b. Stored c. Hit with a hammer d. Cleaned

5. Mariner's compass is used to find the

a. Speed b. Displacement c. Direction d. motion Exercise 2. Fill in the blanks

1. Artificial magnets are made in different shapes, such as , and .

2. The Materials which are attracted towards the magnet are called .

3. Paper is not a material.

4. In olden days, sailors used to find direction by suspending a piece of .

5. A magnet always has POLES.

Exercise 3. True or False if false, give the correct statement. 1. A cylindrical magnet has only one pole. 2. Similar poles of a magnet repel each other. 3. Maximum iron filings stick in the middle of a bar magnet when it is brought near them. 4. A compass can be used to find East-West direction at any place. 5. Rubber is a magnetic material. Exercise 4. Match the following

1. Compass
2. Attraction
3. Repulsion
4. Magnetic Poles

Options: Maximum magnetic strength, Like poles, Opposite poles, Magnetic needle

Exercise 5. Circle the odd ones and give reasons

1. Iron nail, pins, rubber tube, needle.

Odd one out:

Reason:

2. Lift, escalator, electromagnetic train, electric bulb.

Odd one out:

Reason:

3. Attraction, repulsion, pointing direction, illumination.

Odd one out:

Reason:

Exercise 6. The following diagrams show two magnets near one another. Use the words, 'Attract, Repel, Turn around' to describe what happens in each case. Exercise 7. Write down the names of substances. Exercise 8. Give Short answer

1. Explain the attraction and repulsion between magnetic poles.

2. A Student who checked some magnets in the school laboratory found out that their magnetic force is worn out. Give three reasons for that?

Exercise 9. Answer in detail

1. You are provided with an iron needle. How will you magnetize it?

2. How does the electromagnetic train work?

Exercise 10. Questions based on Higher Order Thinking skills

1. You are provided with iron filings and a bar magnet without labelling the poles of the magnet. Using this How will you identify the poles of the magnet? Which part of the bar magnet attracts more iron fillings? Why?

2. Two bar magnets are given in the figure A and B. By the property of attraction, identify the North pole and the South Pole in the bar magnet (B)

3. Take a glass of water with a few pins inside. How will you take out the pins without dipping your hands into water?

📝 Summary

1. Magnets were discovered as natural magnetic rocks called magnetite, which were found to attract iron materials and were named after Magnus or the place Magnesia where they were found.
2. Artificial magnets are man-made magnets available in various shapes including bar magnets, horseshoe magnets, ring magnets, needle magnets, oval shapes, disc shapes, and cylindrical magnets.
3. Materials are classified as magnetic substances (like iron, cobalt, nickel) which are attracted by magnets, and non-magnetic substances (like paper, plastic) which are not attracted by magnets.
4. Magnetic poles are the parts of a magnet where the attractive force is strongest, located at the two ends of the magnet where the largest amount of iron filings stick.
5. Magnets can be used for finding directions by suspending a bar magnet with thread from its center and observing the direction in which it naturally aligns.