➖ Like poles repel
North pole facing north pole, or south pole facing south pole. The magnets push each other away.
Magnetism » Magnets and Magnetic Materials
What you'll learn this session
Study time: 30 minutes
Edexcel spec: 6.2, 6.3, 6.5
- How magnets attract and repel, and which materials are magnetic
- Why repulsion is the only sure test for a magnet
- The difference between magnetically hard and magnetically soft materials, and a use of each
- How a magnet can make some materials into temporary magnets (induced magnetism)
🔒 Unlock Full Course Content
Sign up to access the complete lesson and track your progress!
Unlock This CoursePoles, attraction and repulsion
A magnet is an object that attracts some other materials and can attract or repel other magnets. Every magnet has two ends where the pull is strongest. These ends are called poles. One is the north pole (N) and the other is the south pole (S).
Two magnets act on each other without touching. The rule is short:
➕ Unlike poles attract
North pole facing south pole. The magnets pull towards each other.
You can feel this if you hold two bar magnets near each other. One way round they snap together. Turn one magnet around and they push apart, even though nothing is touching.
Key terms:
- Magnet: an object that attracts magnetic materials and attracts or repels other magnets.
- Pole: one of the two ends of a magnet where the magnetic force is strongest (north pole and south pole).
- Magnetic material: a material that is attracted by a magnet.
Magnetic materials
A magnet does not attract everything. It attracts only magnetic materials. The four you need to know are:
- iron
- steel (which is mostly iron)
- nickel
- cobalt
Most other materials are not attracted. Copper, aluminium, gold, plastic, wood, glass and paper are all non-magnetic. Many people think that all metals are magnetic. That is not true: only a few are.
Notice the difference between a magnet and a magnetic material. A bar magnet attracts a piece of iron. But a piece of unmagnetised iron does not repel a magnet. Iron is a magnetic material, not (yet) a magnet.
Learn this
Both ends of a magnet attract an unmagnetised piece of iron, steel, nickel or cobalt. Attraction does not prove that an object is a magnet. Repulsion is the only sure test for a magnet.
Here is why. Suppose you hold a steel bar near the north pole of a magnet and it is attracted. The bar could be a magnet with its south pole nearest. But it could just as well be an ordinary piece of unmagnetised steel. Both give attraction. If the bar is pushed away, only a magnet can do that, because the end of the bar nearest must be a north pole. So to test whether a bar is a magnet, bring each end of it up to a known pole. If either end is repelled, the bar is a magnet.
Induced magnetism
Why does a magnet attract an unmagnetised piece of iron? The magnet turns the iron into a magnet while it is close. This is called induced magnetism. Magnetism is induced in some materials (iron, steel, nickel and cobalt) when they are placed in a magnetic field. A magnetic field is the space around a magnet where its magnetic force acts. You will study how to draw it in the next lessons.
Follow what happens when you bring the north pole of a bar magnet close to an iron nail:
- The nail is in the magnetic field of the magnet.
- Magnetism is induced in the nail. The end of the nail nearest the north pole becomes a south pole. The far end becomes a north pole.
- The nearest poles are unlike, so they attract. The nail is pulled towards the magnet.
The nearest induced pole is always the opposite of the pole that is close. This is why a magnet attracts a magnetic material whichever pole you use. It is also why you can never get repulsion from an unmagnetised piece of iron.
A chain of paperclips
Hold a magnet over a pile of paperclips. Paperclips are made of a magnetically soft steel, so they are easy to magnetise. The first clip is attracted and becomes an induced magnet. It then attracts a second clip, which becomes an induced magnet too, and so on. You can lift a hanging chain of paperclips. Pull the magnet away and most of the clips fall apart, because most of their induced magnetism has gone.
Magnetically hard and soft materials
Different magnetic materials behave differently after the magnet has gone. You need to be able to describe the properties of magnetically soft and magnetically hard materials.
| Magnetically soft | Magnetically hard | |
|---|---|---|
| Example | iron | steel |
| Becoming magnetised | easy to magnetise | harder to magnetise |
| Keeping its magnetism | loses its magnetism easily, so it makes a temporary magnet | keeps its magnetism, so it makes a permanent magnet |
| A use | the core of an electromagnet | a permanent magnet, for example a compass needle |
🔩 Soft iron: temporary
An iron nail next to a magnet becomes a strong magnet quickly. Take the magnet away and the nail loses its magnetism almost at once. This is ideal when you want a magnet that can be switched on and off. Soft iron is used in the core of electromagnets, which you will meet in Solenoids and Electromagnets.
🧭 Steel: permanent
Steel takes more effort to magnetise, but once it is magnetised it stays magnetised. This is what you want for a permanent magnet, such as a compass needle.
Here, "hard" and "soft" describe how a material behaves magnetically. They do not describe how strong or bendy it is.
Worked example
Question: A student has a steel bar. It is attracted to the north pole of a magnet. The student says, "The bar must be a magnet." Explain whether the student is correct.
Step 1: Steel is a magnetic material, so an unmagnetised steel bar is attracted to either pole of a magnet by induced magnetism.
Step 2: A magnetised steel bar with its south pole nearest would also be attracted.
Step 3: Attraction therefore cannot tell the two cases apart.
Answer: The student is not correct. The bar could be unmagnetised steel. The student should check whether one end of the bar is repelled, because only a magnet can repel another magnet.
Common mistakes
- Saying that all metals are magnetic. Copper, aluminium and gold are not. Only iron, steel, nickel and cobalt are on the list.
- Using attraction as proof that something is a magnet. Repulsion is the only sure test.
- Writing that "hard" means strong or difficult to bend. Magnetically hard means it keeps its magnetism.
- Saying a magnet attracts a nail because the nail is already a magnet. The magnet induces the magnetism in the nail.
Exam-style question
(a) State what happens when the north pole of one bar magnet is brought close to the south pole of another bar magnet. [1 mark]
(b) A student has a bar that might be a magnet or might be an unmagnetised piece of iron. Describe a test that shows which it is. [2 marks]
(c) A soft iron nail is held near the north pole of a magnet and picks up a small iron pin. Explain why the nail attracts the pin, and why the pin falls when the magnet is taken away. [3 marks]
(d) Give one reason why steel is used for a compass needle but soft iron is not. [1 mark]
Model answer
(a) The two magnets attract each other. (1)
(b) Bring one end of the bar close to a pole of a known magnet. (1) If the bar is repelled, it is a magnet. If neither end of the bar is ever repelled, it is unmagnetised iron. (1)
(c) The nail is in the magnetic field of the magnet, so magnetism is induced in it and it becomes a magnet. (1) The nail then induces an opposite pole in the pin, so the pin is attracted. (1) When the magnet is taken away, soft iron loses its magnetism easily, so the nail can no longer hold the pin. (1)
(d) Steel is magnetically hard, so it keeps its magnetism and stays a permanent magnet. Soft iron would lose its magnetism. (1)
Exam tip
When a question asks you to explain how an iron nail or a paperclip is attracted, use the word induced and say which end becomes which pole. A bare "it is magnetic" will not earn the mark.