Magnets: Polarity, Attraction and Repulsion
Hold two magnets close and you can feel an invisible force push back or pull together, no touching needed. Every magnet plays by one simple rule of poles.
Printable Worksheets
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- Describe how magnets attract or repel each other based on their polarity. (SC4-FOR-01)
- Conduct a practical investigation to test the effect of distance on the action of a magnet. (SC4-WS-01)
Q1 · You bring two fridge magnets together and they push apart. You flip one over and now they pull together. What do you think is different about the two ends of a magnet?
Q2 · A magnet on a string can pick up a paper clip without touching it at first. Do you think the pull is the same strength near and far? Why?
● Know
- Every magnet has two poles, a north (N) pole and a south (S) pole
- The rule of polarity: like poles repel and unlike poles attract
- Which materials are magnetic: iron, nickel, cobalt and steel
● Understand
- That magnetism is a non-contact force that acts across a gap
- Why a compass needle lines up with Earth's magnetic field
- That the magnetic force gets weaker as distance increases
● Can do
- Predict whether two magnets will attract or repel
- Plan a fair test of how distance changes a magnet's pull
- Handle magnets safely during a practical investigation
Hold a bar magnet and you cannot see anything happening, but the ends are not the same. Every magnet has two poles: a north pole (marked N) and a south pole (marked S). The force a magnet makes is strongest at its poles.
Poles always come in pairs. You can never get a magnet with only a north pole or only a south pole. If you cut a bar magnet in half, you do not end up with a separate N piece and a separate S piece. Instead, each smaller piece becomes a whole new magnet with its own north pole and its own south pole.
The behaviour of two magnets depends only on which poles face each other. This is the rule of polarity:
- Like poles repel. Two north poles (N and N) push apart. Two south poles (S and S) push apart.
- Unlike poles attract. A north pole and a south pole (N and S) pull together.
Because magnetism works across a gap, it is a non-contact force. You can feel two magnets push or pull before they ever touch. The closer the poles get, the stronger this push or pull becomes.
Magnets do not attract everything. Only certain magnetic materials are pulled toward a magnet:
- Iron the most common magnetic metal
- Nickel used in some coins
- Cobalt a strong magnetic metal
- Steel magnetic because it contains iron
Most materials are not magnetic. Plastic, wood, glass, copper and aluminium are not attracted to a magnet at all. A quick test is to touch an object with a magnet: if it grips, it contains a magnetic metal such as iron.
A compass is a very useful magnet. The needle inside a compass is a tiny bar magnet that can spin freely. Because Earth itself acts like a giant magnet, it has a magnetic field all around it. The compass needle lines up with Earth's magnetic field, so its north-seeking pole points roughly toward Earth's north. This is how explorers and bushwalkers have found their way for centuries.
Australian context: the magnetic compass on a four-wheel drive in the outback still works the same way as one used by early explorers crossing the continent. The needle is just a small magnet swinging to line up with Earth's magnetic field.
The magnetic force is not the same at every distance. The closer an object is to a magnet, the stronger the pull. As you move the object further away, the force gets weaker very quickly. Hold a magnet a few centimetres from a paper clip and nothing happens, but slide it closer and suddenly the clip jumps across to the magnet.
You can investigate this yourself with a simple, safe fair test. One easy method is to count how many paper clips a magnet can hold through an increasing number of sheets of paper or cards. Each extra sheet pushes the paper clip a little further from the magnet, so the magnet should hold fewer clips. Another method is to slowly slide a magnet toward a single paper clip and measure the distance at which the clip first moves.
To make it a fair test, you change only ONE thing (the variable):
- Change: the distance between the magnet and the paper clip (for example, the number of paper sheets in the gap)
- Keep the same: the same magnet, the same paper clips, the same surface, the same way of measuring
- Measure: how many clips are held, or the distance at which the clip first moves
You hold a magnet over a single paper clip and slowly add sheets of paper into the gap, one at a time. What do you predict will happen to the magnet's ability to lift the clip as you add more sheets? Why?
How close was your prediction?
Well done, you predicted that more distance means a weaker magnetic force.
Key insight: magnetic force gets weaker as distance increases, so more sheets means fewer clips lifted.
For each pair of magnet ends below, decide whether they will attract (pull together) or repel (push apart). Then say whether each pair is "like poles" or "unlike poles".
| # | Poles facing each other | Attract or repel? | Like or unlike? |
|---|---|---|---|
| 1 | North pole facing a south pole | ||
| 2 | North pole facing a north pole | ||
| 3 | South pole facing a south pole | ||
| 4 | South pole facing a north pole | ||
| 5 | A north pole near a steel paper clip |
For row 5, remember a paper clip is not a magnet but it is a magnetic material. Will it be pulled toward the magnet or pushed away?
This is the practical investigation for the syllabus: test the effect of distance on the action of a magnet. Read the safety note above first, then plan your fair test.
What you need: one bar magnet (a larger classroom magnet, not tiny magnet balls), a pile of paper clips, and several sheets of paper or thin card.
Method:
- Place 1 sheet of paper over a pile of paper clips. Lower the magnet onto the sheet and count how many clips it lifts.
- Add another sheet so there are 2 sheets, then 3, then 4, then 5, increasing the distance each time.
- Each time, record how many paper clips the magnet can lift.
Fair test: the variable you change is the distance (number of sheets). Keep the magnet, the paper clips and the way you measure exactly the same every time.
Fill in a results table like this in your book, then answer the questions below.
| Number of sheets (distance) | Paper clips lifted |
|---|---|
| 1 | |
| 2 | |
| 3 | |
| 4 | |
| 5 |
Q1. State the rule of polarity for magnets. Use the words "like poles" and "unlike poles" in your answer. (2 marks)
Q2. Describe how you could carry out a fair test to find out how distance affects the action of a magnet. State the variable you change, one thing you keep the same, and what you measure. (3 marks)
Q3. A student says a magnet must touch a paper clip to move it. Explain why this is wrong, using the idea of a non-contact force and how distance changes the strength of the force. (3 marks)
Answers
▾MCQ 1
B Every magnet has exactly two poles, a north pole and a south pole. Poles always come in pairs, even if you cut the magnet into smaller pieces.
MCQ 2
B Two south poles are like poles, and like poles repel, so they push apart. They do not change into other poles or do nothing.
MCQ 3
C Iron is a magnetic material and is attracted to a magnet. Plastic, wood and copper are not magnetic, so a magnet does not attract them.
MCQ 4
B Magnetic force gets weaker as distance increases. Moving the paper clip further away makes the pull smaller, until eventually it is too weak to move the clip.
MCQ 5
C A compass needle is a tiny magnet that can spin freely. It lines up with Earth's magnetic field, so its north-seeking pole points roughly toward Earth's north.
Short Answer 1
Model answer: Like poles repel and unlike poles attract. Two north poles, or two south poles, are like poles and push apart. A north pole and a south pole are unlike poles and pull together.
Short Answer 2
Model answer: Place paper clips under a magnet and add sheets of paper one at a time to increase the distance. The variable I change is the distance (number of sheets). I keep the same magnet, the same paper clips and the same way of measuring. I measure how many paper clips the magnet can lift at each distance. As distance increases, the magnet should lift fewer clips because the magnetic force gets weaker.
Short Answer 3
Model answer: The student is wrong because magnetism is a non-contact force, so a magnet can pull a magnetic material such as a paper clip across a gap without touching it. The force is stronger when the magnet is close to the clip and weaker when it is far away. When the magnet is close enough, the force is strong enough to make the clip jump across to it, even though they were not touching at first.
At the start of this lesson you saw the hook: two magnets that pushed apart, then pulled together after you flipped one over. Now you know why, it all comes down to which poles face each other. Like poles repel and unlike poles attract.
How does your new understanding of poles compare to what you first thought? Explain in your own words why the magnetic force felt stronger when the magnets were close together than when they were far apart.
- Every magnet has two poles, a north pole and a south pole, and poles always come in pairs.
- The rule of polarity: like poles repel (N and N, or S and S) and unlike poles attract (N and S). Magnetism is a non-contact force.
- Magnetic materials are iron, nickel, cobalt and steel. The magnetic force gets weaker as distance increases, which you can test with a fair experiment.