Magnets: The Complete P3 Science Guide

Magnets are all around us — from the tiny magnets in your phone's speaker to the massive electromagnets used in hospitals and scrapyards. In P3 Science, you learn the fundamentals of magnetism: what materials are attracted to magnets, how the poles of magnets interact, and how magnetic force can act without touching. These concepts are not only tested at PSLE but are the foundation for understanding electricity and motors in later years.

Magnetic and Non-Magnetic Materials

Only certain materials are attracted to magnets. These are called magnetic materials. The four magnetic materials you must know for PSLE are:

• Iron (Fe) — the most commonly tested magnetic material
• Steel — an alloy made mostly of iron, so it is also magnetic
• Nickel (Ni) — less commonly seen in everyday life but important for exams
• Cobalt (Co) — used in strong permanent magnets

A critical exam point: not all metals are magnetic. Many students assume all metals are attracted to magnets, but this is incorrect. The following metals are NOT magnetic:

• Copper — used in electrical wires; not attracted to magnets
• Aluminium — used in drink cans, kitchen foil; not attracted to magnets
• Gold and silver — precious metals; not attracted to magnets
• Zinc, tin, lead — also non-magnetic metals

Non-metals such as wood, plastic, glass, rubber, and paper are also not attracted to magnets. Only iron, steel, nickel, and cobalt are reliable magnetic materials at PSLE level.

The Poles of a Magnet

Every magnet has two poles — a North pole (N) and a South pole (S). The poles are the regions where the magnetic force is strongest. The centre of a bar magnet has the weakest magnetic force. When you suspend a bar magnet freely, the North pole points towards Earth's geographic North Pole (because Earth itself acts as a giant magnet).

The fundamental rule of magnetic poles:

Like poles REPEL (push apart)  |  Unlike poles ATTRACT (pull together)

• N pole + N pole → REPEL (they push away from each other)
• S pole + S pole → REPEL
• N pole + S pole → ATTRACT (they pull toward each other)
• S pole + N pole → ATTRACT

This rule applies to all magnets. It is tested in diagrams where you must predict whether two magnets will attract or repel based on which poles face each other, and in questions about compass needle behaviour.

Magnetic Force — A Non-Contact Force

One of the most remarkable features of magnetic force is that it can act without the magnet physically touching the object. This makes it a non-contact force. A magnet can attract an iron nail through a piece of paper, through a plastic bag, through water, or even through your hand — without any direct contact between the magnet and the nail.

The only requirement is that the distance is not too great. Magnetic force weakens rapidly as distance increases — doubling the distance reduces the force significantly. At very large distances, the force is essentially zero.

Materials that magnetic force can pass through (non-magnetic materials): paper, cardboard, plastic, glass, water, wood, cloth, your hand, thin metals (copper, aluminium). Materials that can block or reduce magnetic force: thick iron or steel plates (these are used in magnetic shielding).

Permanent Magnets and Temporary Magnets

A permanent magnet is one that retains its magnetism indefinitely under normal conditions. These are made from steel, alnico (aluminium-nickel-cobalt alloy), or rare-earth materials. Bar magnets, horseshoe magnets, and button magnets found in schools are usually permanent magnets.

A temporary magnet only behaves as a magnet when a magnetic field is present — for example, a piece of iron that becomes magnetised when placed near a magnet, but loses its magnetism when the magnet is removed. Iron is a soft magnetic material that easily magnetises and demagnetises.

Magnets can be demagnetised (made to lose their magnetic properties) by: hammering them, heating them strongly, or repeatedly dropping them. These actions disrupt the alignment of the tiny magnetic domains inside the material.

Making a Magnet by Stroking

You can make a temporary magnet by stroking an iron or steel object repeatedly in the same direction with a permanent magnet. This is called the stroking method. Each stroke aligns the magnetic domains in the iron in the same direction, building up a net magnetic field. The direction of stroking determines which end becomes the North pole and which becomes the South pole.

Key rule: always stroke in the same direction (do not stroke back and forth) and always use the same pole of the magnet throughout. Random stroking in both directions cancels out the alignment.

The Compass and Earth's Magnetic Field

A compass is simply a tiny magnet (the compass needle) balanced on a pivot so it can spin freely. Because Earth has a magnetic field (caused by its molten iron core), the compass needle aligns with Earth's field — the North pole of the needle points toward Earth's geographic North Pole.

This is why compasses have been used for navigation for over 2,000 years. When you use a compass near a strong magnet, the needle is deflected away from North and points toward the magnet's South pole instead — this is how you can tell whether a magnetic field is present and how strong it is.

The difference between geographic North (true North) and magnetic North is called magnetic declination. Near Singapore's latitude, this difference is small but measurable. For PSLE, simply know that a compass needle points North because Earth has a magnetic field, and that nearby magnets can deflect the needle.

Real-World Applications of Magnets

Magnets have countless practical applications, many of which appear in PSLE exam questions:

• Magnetic door catches — keep refrigerator and cabinet doors closed using magnetic attraction between a magnet and a steel plate
• Credit cards and hotel key cards — contain a magnetic stripe storing encoded data
• Speakers and headphones — use electromagnets to convert electrical signals into sound vibrations
• MRI machines — use extremely powerful magnets to create detailed images of the inside of the body
• Maglev trains — float above the track using magnetic repulsion, eliminating friction for extremely high speeds
• Scrapyard cranes — use large electromagnets to pick up and move scrap iron and steel
• Separating iron from mixtures — in recycling plants, magnets separate iron and steel from non-magnetic materials like aluminium and plastic