Investigating electromagnets
In this topic you will:
- discover which factors (or variables) affect the strength of an electromagnet
- investigate how these variables affect the strength of an electromagnet.
Key words
- demagnetised
- factors
- soft iron
Strength of electromagnets
Last topic listed the three things that are needed to make an electromagnet:
- a coil of wire
- a magnetic core inside the coil
- an electric current flowing in the coil.
These three things give the factors that will affect the strength of an electromagnet. A factor is another word for a variable that will affect something.
- The number of turns in the coil. The more turns in the coil, the stronger the electromagnet.
- The material of the core. Iron and some types of steel in the core make the strongest electromagnets.
- The current in the coil. The greater the current, the stronger the electromagnet.
The diagrams show the three ways to increase the strength of an electromagnet:
1 Increase the number of turns on the coil. Keep the current and core the same.
2 Use more cells to increase the current. Keep the number of turns on the coil and the core the same.
3 Use a soft iron core in place of a steel core. Keep the number of turns on the coil and the current the same.
Common Mistake
Don’t confuse the number of turns with the thickness of the wire. It’s the number of turns — not wire thickness — that affects the strength of the electromagnet.
Soft iron is not soft in the same way as modelling clay is soft.
Soft iron is the term used for iron that is easily magnetised and also easily demagnetised. Demagnetised means it has lost its magnetism.
In 2019, scientists broke the world record for the strongest electromagnet. They made an electromagnet 4500 times stronger than a school bar magnet. It uses more electricity than three million electric lamps!
The strength of an electromagnet can be measured by the force that the electromagnet exerts on a magnetic material. The easiest way to do this is to see how many magnetic objects that the electromagnet can lift and hold.
Quick Fact
The world’s strongest electromagnet in 2019 required over 30 megawatts of power — about the same as a small town!
Questions
Show Answer
Sorting scrap metal requires lifting heavier, bulkier objects. A stronger electromagnet is needed to create enough magnetic force to lift and move them, unlike the lighter task of holding a toaster handle.
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1. The number of turns in the coil
2. The material of the core
3. The size of the current in the coil
Write one letter.
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Nickel is a magnetic material and makes a strong electromagnet. The correct answer is C.
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CERN uses powerful electromagnets to accelerate particles to near the speed of light. These magnets require very high currents, which use a large amount of electricity.
Think Like a Scientist
Investigating electromagnet strength
In this investigation, you will explore how different variables affect the strength of an electromagnet. You will test how the number of coil turns, the core material, and the current in the coil influence the number of paperclips picked up.
Equipment you will need:
• Three 1.5 V cells or adjustable d.c. power supply with safety cut-out
• Leads and connectors, switch, ammeter, iron nail
• Paperclips of different sizes
• Plastic-coated wire (1 m, stripped at both ends)
• Selection of similar-sized core materials (e.g. pencil, paper roll, pen, metal rod)
⚠️ Safety
Only keep the electromagnet switched on for the shortest time possible to avoid draining the cells.
Check the coil wire frequently. If it becomes hot, switch off the circuit immediately and inform your teacher.
Part 1 – Changing the number of turns in the coil
Step 1: Wrap the wire around the iron nail to make five turns.
Step 2: Connect the circuit and turn on the electromagnet. Record how many paperclips it picks up.
Step 3: Switch off, add five more turns to the coil.
Step 4: Repeat the test and record the number of paperclips picked up.
Step 5: Continue increasing the number of turns in steps of five until no more turns can fit.
Step 6: Repeat the full investigation to check consistency.
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Create a table with columns for "Number of Turns" and "Paperclips Held".
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Add repeated results and divide by the number of trials for each value.
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Use “Number of Turns” on the horizontal axis and “Average Paperclips Held” on the vertical axis.
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The number of paperclips picked up increases as the number of turns increases.
Part 2 – Changing the core material
Step 1: Wrap the maximum number of turns around the iron nail.
Step 2: Test how many paperclips it picks up.
Step 3: Repeat the test with other core materials of the same diameter.
Step 4: Repeat each test for reliability.
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Use a table with "Core Material" and "Paperclips Held" columns.
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Average your repeated results for each core type.
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Use core materials on the x-axis and average number of paperclips on the y-axis.
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Some core materials make stronger electromagnets than others.
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Line graphs are for continuous data (turns), while bar charts suit discrete data (materials).
Part 3 – Changing the current in the coil
In this part, you will plan your own investigation.
Step 1: Choose which variable (e.g. current) to change.
Step 2: Decide what to control.
Step 3: Draw a circuit diagram.
Step 4: Make a prediction.
Step 5: Choose paperclip type and justify.
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Use a line graph if current values are numerical and continuous.
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Sketch or plot a graph with current on x-axis and paperclips on y-axis.
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Compare your predicted and actual results. Reflect on possible reasons for differences.
Self-assessment
- I can recall the three factors that affect electromagnet strength.
- I could plan an investigation to test the effect of changing one of these factors.
- I can understand whether a line graph or bar chart is more suitable for presenting results.