1.0 Introduction to Magnetism
A magnet is a special object that can attract certain materials towards itself. If we bring a magnet near iron pins, paper clips or small nails, they get attracted to the magnet. This attractive property of a magnet is called magnetism.
Magnetism is a very useful force in daily life. We use magnets in compass needles, refrigerator doors, speakers, toys, motors and many machines. A magnet does not attract all objects. It attracts only some materials.
Statement: A magnet is an object that attracts magnetic materials such as iron, nickel and cobalt.
Statement: Magnetism is the property by which a magnet attracts certain materials towards itself.
Materials that are attracted by a magnet are called magnetic materials. Iron, nickel and cobalt are common magnetic materials. Many objects made of iron or steel, such as nails, pins and paper clips, are attracted by magnets.
Materials that are not attracted by a magnet are called non-magnetic materials. Wood, plastic, rubber, glass, paper and cloth are examples of non-magnetic materials. A magnet will not attract a wooden pencil or a plastic ruler.
Why does a magnet attract some objects but not others? A magnet attracts materials that have magnetic properties, such as iron, nickel and cobalt. Materials like plastic, wood and rubber do not have these magnetic properties, so they are not attracted by magnets.
A fridge magnet sticks to a refrigerator door because the door contains magnetic material. But the same magnet will not stick to a wooden door or plastic chair because wood and plastic are non-magnetic materials.
| Type of Material | Meaning | Examples |
|---|---|---|
| Magnetic Materials | Materials attracted by a magnet | Iron, nickel, cobalt, steel paper clip |
| Non-Magnetic Materials | Materials not attracted by a magnet | Wood, plastic, rubber, glass, paper |
A simple activity can help us test whether a material is magnetic or non-magnetic. Bring a magnet near different objects such as a nail, coin, pencil, eraser, paper clip and plastic ruler. Objects that move towards the magnet are magnetic. Objects that do not move towards the magnet are non-magnetic.
Do not write that all metals are magnetic. Iron, nickel and cobalt are magnetic, but many metals like aluminium, copper and gold are not attracted by ordinary magnets.
INC helps you remember common magnetic materials:
I = Iron
N = Nickel
C = Cobalt
Steel is made mainly from iron, so many steel objects are attracted by magnets. That is why steel paper clips and steel pins usually stick to magnets.
- A magnet attracts magnetic materials such as iron, nickel and cobalt.
- Magnetism is the property by which a magnet attracts certain materials.
- Wood, plastic, rubber, glass and paper are non-magnetic materials.
Why does a magnet attract an iron nail but not a plastic ruler?
2.0 Poles of a Magnet and Magnetic Force
Every magnet has two ends where its magnetic force is the strongest. These two ends are called the poles of a magnet. One end is called the North pole, and the other end is called the South pole.
Statement: The two ends of a magnet where magnetic force is strongest are called magnetic poles.
If we dip a bar magnet into iron filings, most filings stick near the two ends of the magnet. Very few filings stick near the middle. This shows that magnetic force is strongest at the poles and weaker near the middle.
Why are iron filings mostly attracted near the ends of a magnet? The magnetic force is strongest at the two poles. Since the ends have stronger magnetic attraction, more iron filings collect there.
When two magnets are brought close, their poles interact with each other. If similar poles are brought together, they push away from each other. If opposite poles are brought together, they pull towards each other.
Statement: Like poles repel each other, while unlike poles attract each other.
| Poles Brought Together | Result | Meaning |
|---|---|---|
| North pole + North pole | Repulsion | They push away from each other |
| South pole + South pole | Repulsion | They push away from each other |
| North pole + South pole | Attraction | They pull towards each other |
Magnetic force is a non-contact force. This means it can act even when the magnet is not touching the object. For example, a magnet can attract iron pins from a small distance without touching them directly.
Fridge magnets stick to refrigerator doors because of magnetic attraction. A compass needle turns and points roughly in the north-south direction because it behaves like a tiny magnet and responds to Earth's magnetism.
A magnet cannot have only one pole. If a bar magnet is broken into two pieces, each piece gets both a North pole and a South pole.
Like = Leave, Unlike = Unite
Like poles move away from each other. Unlike poles come together.
Earth behaves like a giant magnet. This is why a freely suspended magnet or compass needle points in the north-south direction.
- Every magnet has two poles: North pole and South pole.
- Magnetic force is strongest at the poles.
- Like poles repel, while unlike poles attract.
What will happen if the North pole of one magnet is brought near the North pole of another magnet?
3.0 Magnetic Field and Magnetic Lines of Force
A magnet can attract magnetic materials even without touching them. This happens because a magnet has an invisible region around it where its magnetic force can be felt. This region is called the magnetic field.
Statement: The region around a magnet where its magnetic force can be felt is called its magnetic field.
The magnetic field is not visible to our eyes. But we can observe its effect using iron filings or a compass. When iron filings are sprinkled around a bar magnet, they arrange themselves in a pattern. This pattern shows the shape of the magnetic field around the magnet.
Why do iron filings form a pattern around a magnet? Each iron filing behaves like a tiny temporary magnet. When it comes near a magnet, it gets arranged along the magnetic field. This makes the invisible magnetic field visible as a pattern.
The curved paths shown by iron filings around a magnet are called magnetic lines of force. These lines help us understand the direction and strength of the magnetic field. The lines are closer near the poles because the magnetic force is stronger there.
Statement: Magnetic lines of force are imaginary lines used to represent the magnetic field around a magnet.
Outside a magnet, magnetic field lines are shown from the North pole to the South pole. This direction is useful when drawing magnetic field diagrams. The field lines never cross each other.
| Feature | Meaning | Exam Point |
|---|---|---|
| Magnetic Field | Region where magnetic force is felt | It is strongest near the poles |
| Field Lines | Imaginary lines showing magnetic field | They go from North to South outside the magnet |
| Closer Lines | Stronger magnetic field | Seen mostly near the poles |
A compass needle moves because it is affected by magnetic fields. Earth has its own magnetic field, so a compass needle aligns roughly in the north-south direction. This is why sailors and travellers used compasses for direction before modern GPS.
Do not say magnetic field lines are real wires or strings around a magnet. They are imaginary lines used to show the direction and pattern of the magnetic field.
N to S Outside
Magnetic field lines outside a magnet are shown from North pole to South pole.
The closer the magnetic field lines are, the stronger the magnetic field is. This is why the magnetic field is shown crowded near the poles of a bar magnet.
- The region around a magnet where magnetic force acts is called magnetic field.
- Magnetic field lines are imaginary lines showing the magnetic field pattern.
- Outside a magnet, magnetic field lines are shown from North pole to South pole.
Why do iron filings form curved patterns around a bar magnet?
4.0 Types of Magnets and Uses of Magnets
Magnets are of different types and shapes. Some magnets are found in nature, while many magnets are made by humans for different uses. Magnets may look small, but they are used in many important devices around us.
Statement: Natural magnets are magnets found in nature, while artificial magnets are magnets made by humans.
A naturally occurring magnetic rock is called lodestone. It is a natural magnet. However, natural magnets are not very convenient for daily use because they may be irregular in shape and not very strong.
Most magnets used today are artificial magnets. These are made in different shapes and strengths according to their use. Bar magnets, horseshoe magnets, ring magnets and cylindrical magnets are common examples.
Why are artificial magnets more useful than natural magnets? Artificial magnets can be made in required shapes, sizes and strengths. For example, a bar magnet is useful in school experiments, while small circular magnets are useful in toys and electronic devices.
Magnets can also be described as temporary magnets and permanent magnets. A temporary magnet behaves like a magnet only for a short time. A permanent magnet keeps its magnetism for a long time.
Statement: A temporary magnet loses its magnetism quickly, while a permanent magnet retains its magnetism for a long time.
| Type of Magnet | Meaning | Example |
|---|---|---|
| Natural Magnet | Found in nature | Lodestone |
| Artificial Magnet | Made by humans | Bar magnet, horseshoe magnet |
| Temporary Magnet | Shows magnetism for a short time | Iron nail near a strong magnet |
| Permanent Magnet | Keeps magnetism for a long time | Bar magnet, fridge magnet |
Magnets are used in compass needles, refrigerator doors, electric bells, speakers, motors, toys, magnetic pencil boxes and cranes used in scrap yards. A magnetic crane can lift heavy iron pieces because iron is attracted by magnets.
A compass contains a tiny magnetized needle. The needle can rotate freely and points roughly in the north-south direction. This helps people find directions. In earlier times, sailors and travellers used compasses to navigate.
Magnets are also used in speakers and headphones. They help convert electrical signals into sound. In electric motors, magnets help produce motion. This shows that magnetism is useful not only in simple school experiments, but also in technology.
| Use of Magnet | How Magnet Helps |
|---|---|
| Compass | Magnetic needle helps find direction |
| Refrigerator Door | Magnetic strip helps the door close tightly |
| Speaker | Magnet helps produce sound |
| Magnetic Crane | Lifts heavy iron and steel objects |
Do not write that all metals are attracted by magnets. Only some materials, mainly iron, nickel, cobalt and many steel objects, are attracted by ordinary magnets.
Compass, Crane, Closing Door
Magnets help in finding directions, lifting iron and closing refrigerator doors.
Magnetic cranes are used in scrap yards to separate iron and steel from waste materials. This makes recycling faster and easier.
- Magnets may be natural or artificial.
- Magnets can be temporary or permanent.
- Magnets are used in compasses, speakers, refrigerator doors, toys and magnetic cranes.
Why is a compass useful for finding directions?
5.0 Care, Safety, Revision and Exam Readiness
Magnets are useful, but they must be handled and stored carefully. If magnets are heated, hammered, dropped many times or stored wrongly, they may lose their magnetism. A magnet that loses magnetism becomes weaker and may not attract magnetic materials properly.
Statement: Proper storage of magnets helps them retain their magnetic strength for a longer time.
Why should magnets be stored carefully? Inside a magnet, tiny magnetic regions are arranged in an orderly way. Heating, hammering or dropping can disturb this arrangement. When this happens, the magnet becomes weak.
Bar magnets are usually stored in pairs with unlike poles near each other. Soft iron pieces called magnetic keepers are placed across the ends. These keepers help preserve the magnetism of the magnets.
Statement: Magnetic keepers are soft iron pieces placed across the poles of magnets to help preserve their magnetism.
Magnets should be kept away from electronic devices, magnetic cards and watches because strong magnets may affect them. Magnets are useful in many devices, but careless handling can damage sensitive equipment.
Do not store magnets randomly with like poles together for a long time. Magnets should be stored properly using keepers so that they do not lose strength quickly.
| Topic | Quick Revision Point | Example |
|---|---|---|
| Magnet | An object that attracts magnetic materials | Bar magnet, fridge magnet |
| Magnetic Materials | Materials attracted by a magnet | Iron, nickel, cobalt |
| Non-Magnetic Materials | Materials not attracted by a magnet | Wood, plastic, rubber |
| Magnetic Poles | Ends of a magnet where force is strongest | North pole and South pole |
| Rule of Poles | Like poles repel and unlike poles attract | N-N repel, N-S attract |
| Magnetic Field | Region around a magnet where magnetic force acts | Field around a bar magnet |
| Uses of Magnets | Used in devices and tools | Compass, speaker, crane |
No major numerical formula in this chapter
- Key Rule 1: A magnet attracts magnetic materials such as iron, nickel and cobalt.
- Key Rule 2: Every magnet has two poles: North pole and South pole.
- Key Rule 3: Like poles repel, unlike poles attract.
- Key Rule 4: Magnetic field lines outside a magnet are shown from North pole to South pole.
Magnetism Revision = INC + NS + LU
INC = Iron, Nickel, Cobalt are magnetic
NS = North and South poles
LU = Like poles repel, Unlike poles attract
- Define magnetism.
- Name three magnetic materials.
- Give two examples of non-magnetic materials.
- What are magnetic poles?
- State the rule of attraction and repulsion between magnetic poles.
- What is a magnetic field?
- Why should magnets be stored carefully?
- Magnets attract magnetic materials and have two poles.
- Magnetic force is strongest at the poles, and unlike poles attract each other.
- Magnets should be stored carefully to protect their magnetism.
Why should magnets be stored with proper magnetic keepers?