Magnetism

1. Introduction to Magnets

A magnet is an object that attracts materials like iron, nickel, and cobalt.

Magnetic materials: Substances that are attracted to magnets (iron, steel, nickel, cobalt).
Non-magnetic materials: Substances not attracted to magnets (wood, plastic, glass, paper, copper).

2. Types of Magnets

Natural Magnets

• Found in nature.
• Lodestone (magnetite, Fe3O4) is a natural magnet.
• Discovered by the ancient Greeks near Magnesia (hence the name 'magnet').

Artificial Magnets

Made by humans by magnetizing magnetic materials.

Exam Focus (2 marks): 'What is a lodestone? How is it different from an artificial magnet?'

Lodestone is a naturally occurring magnetic rock (magnetite). Artificial magnets are made by humans and can be shaped as needed. Natural magnets are weaker than modern artificial magnets.

3. Properties of Magnets

Basic Properties

1. Attractive property: Magnets attract magnetic materials.
2. Directive property: A freely suspended magnet always aligns in the North-South direction.
3. Like poles repel, unlike poles attract.
4. Poles exist in pairs: Every magnet has a north pole and a south pole.
5. Maximum magnetism at poles: The magnetic force is strongest at the poles and weakest in the middle.

Magnetic Poles

The ends of a magnet where the magnetic force is strongest are called poles.

Every magnet has two poles: North-seeking pole (N) and South-seeking pole (S).

Worked Example: Two bar magnets are brought near each other. Magnet A's north pole is brought close to Magnet B's south pole. What happens?

Unlike poles attract. The two magnets will attract each other.

Common Mistake: Thinking a magnet can have only one pole. This is impossible — if you break a magnet into two, each piece becomes a complete magnet with both poles.

4. Earth as a Magnet

The Earth behaves like a giant bar magnet with its magnetic poles near the geographic poles.

• Earth's magnetic south pole is near the geographic North Pole.
• Earth's magnetic north pole is near the geographic South Pole.

This is why a compass needle's north pole points toward the geographic North Pole (it is attracted to Earth's magnetic south pole).

Interesting fact: Earth's magnetic field protects us from harmful solar radiation by deflecting charged particles from the Sun.

5. Magnetic Compass

A magnetic compass is a device that uses a freely rotating magnetic needle to find directions.

Parts of a compass:

• A small magnetic needle mounted on a pivot.
• The needle is marked with N (north) and S (south).
• A circular dial with cardinal directions (N, S, E, W).

Working:

1. The needle aligns with Earth's magnetic field.
2. The N end of the needle points toward the geographic North Pole.
3. The S end points toward the geographic South Pole.

Worked Example: A hiker uses a compass to find directions. Which direction does the red (north) end of the needle point?

The north end of the compass needle points toward the geographic North Pole of the Earth.

6. Making a Magnet

Single Touch Method

Stroke a steel bar with one pole of a magnet repeatedly in one direction.

Double Touch Method

Use two magnets placed with opposite poles together, stroked from the centre outward.

Electrical Method

Passing electric current through a coil wound around an iron core creates an electromagnet.

7. Comparison Table: Natural vs Artificial Magnets

8. Self-Test

1. Define a magnet. Give two examples of magnetic materials.
2. List three properties of a magnet.
3. Why does a freely suspended magnet always point North-South?
4. What is a magnetic compass? Explain how it works.
5. Differentiate between natural and artificial magnets.
6. What happens when the north pole of one magnet is brought near the north pole of another magnet?
7. Name the shape of magnet used in: (a) laboratory experiments (b) lifting heavy objects.
8. Can a magnet have only one pole? Explain.

9. Answers to Self-Test

1. An object that attracts iron, nickel, cobalt. Magnetic materials: iron, steel, nickel.
2. (a) Attracts magnetic materials. (b) Freely suspended aligns North-South. (c) Like poles repel, unlike attract.
3. Because the Earth itself acts as a giant magnet. The needle aligns with Earth's magnetic field.
4. A device with a magnetic needle that points North. The needle aligns with Earth's magnetic field to show directions.
5. Natural: found in nature (lodestone), weak, irregular shape. Artificial: man-made (bar magnet), can be strong, any shape.
6. Like poles repel, so they will push each other away.
7. (a) Bar magnet (b) U-shaped or horseshoe magnet.
8. No. Poles always exist in pairs. Breaking a magnet creates two smaller magnets, each with both poles.