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Edexcel International GCSE Physics · Section 6 Magnetism and electromagnetism
Electromagnetism: the field round a wire and a solenoid
In this lesson you'll learn to: show that a current in a wire makes a magnetic field
around it, use the right-hand grip rule to get the direction, sketch the field
round a straight wire and round a solenoid, and explain how a solenoid with a
soft iron core becomes an electromagnet you can switch on and off.
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Prefer to watch? Scroll to the bottom for the video on this topic
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A video walkthrough is coming soon — it will appear at the bottom of this page
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Start here — have a play
Don't read anything yet. On scene 1, press Close the switch and watch all eight plotting compasses swing round into a circle. Then press Reverse the current — every needle turns through 180°. On scene 2, switch the solenoid on and untick the soft iron core to see what the core is doing.
What's happening
Conventional current is shown — it flows from + to − round the circuit.
▲ Scene 1: the compasses only line up in circles while the current is flowing. Scene 2: the field lines run straight through the middle of the coil.
Seen what the compasses do? Now learn to draw it.
The examiner asks you to sketch these two field patterns and put the arrows on the right way round. The notes below give you both patterns, the right-hand grip rule, and the trick for working out which end of a solenoid is north.
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Revision notes
A current makes a magnetic field
A magnetic field isn't only made by magnets. Whenever a current flows in a wire, there is a magnetic field around that wire. No current, no field — which is why the compasses in the animation sit pointing north until you close the switch.
The field is real, but it is usually weak. A single wire carrying a small current will only nudge a plotting compass sitting right next to it.
⭐ Key fact
An electric current in a conductor produces a magnetic field around it. The bigger the current, the stronger the field.
The field round a straight wire
The field lines are circles around the wire, at right angles to it. That's why the card in the animation is pushed onto the wire at right angles: the circles lie flat on the card.
- The circles are closest together near the wire — that's where the field is strongest.
- Further out, the circles are further apart, so the field is weaker.
- Every field line has an arrow on it showing the direction the field points.
- Reverse the current and the field reverses too — all the arrows turn round.
✋ The right-hand grip rule — for a straight wire
Grip the wire with your right hand, with your thumb pointing the way the current flows (conventional current, + to −). Your curled fingers then point the way round the field goes.
So a current coming out of the page (⊙) gives an anticlockwise field, and a current going into the page (⊗) gives a clockwise field.
The ⊙ and ⊗ symbols come up constantly in exams. Think of an arrow: ⊙ is the point of the arrow coming towards you, ⊗ is the feathers going away from you.
The field round a solenoid
A solenoid is a long coil of wire. Each turn makes its own circular field, and together they add up to something much stronger and much more useful.
- Outside, the pattern looks exactly like a bar magnet's: the lines leave the north pole, curve right round, and go back in at the south pole.
- Inside, the lines carry straight on through the middle, from S to N, so every line makes a complete loop. Unlike a bar magnet, you can see inside.
- Inside the solenoid the field is strong and uniform — the lines are parallel and evenly spaced, all pointing the same way.
- The solenoid has a north end and a south end, and reversing the current swaps them over.
💡 Which end is north? The N and S trick
Look straight in at one end of the coil and follow the current round:
ANticlockwise = N · clockWISE = S
Write the letter N and put arrowheads on the ends of its strokes — they sweep round anticlockwise. Do the same to an S and it sweeps round clockwise. The letters tell you themselves, so you can't forget it under exam pressure.
Making an electromagnet
Put a soft iron core inside the solenoid and you have an electromagnet. The iron becomes magnetised by the coil's field, and the field becomes much stronger.
The great advantage over a bar magnet: you can switch it on and off, and you can change how strong it is.
| To make an electromagnet stronger | Why |
|---|---|
| Increase the current | A bigger current makes a stronger field around every turn. |
| Add more turns on the coil | Each turn adds its own field to the total. |
| Add a soft iron core | Iron magnetises easily, which concentrates and strengthens the field. |
⭐ Why the core must be SOFT iron
Soft magnetic materials (like iron) magnetise easily and lose their magnetism as soon as the current stops. That is exactly what an electromagnet needs.
Hard magnetic materials (like steel) keep their magnetism — useful for a permanent magnet, useless here, because the magnet would never switch off.
Electromagnets are used anywhere you need a magnet you can control: scrapyard cranes lifting and dropping cars, relays and circuit breakers, electric bells, and the magnetic locks on doors.
💡 Exam tip — drawing the patterns
Marks are dropped for the small things. Every field line needs an arrow. Field lines never cross. Round a wire they are circles, not blobs. Inside a solenoid they must be parallel and evenly spaced — that's what "uniform" looks like on paper.
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How it comes up in the exam
Question 1 · 3 marks
A vertical wire passes through a horizontal card. The current flows downwards. Sketch the magnetic field on the card, and state what happens to it if the current is reversed.
Looking down from above, the current goes into the page (⊗), so by the right-hand grip rule the field is clockwise. Draw at least three circles round the wire, closer together near the wire, each with an arrowhead going clockwise. If the current is reversed, the field lines stay in the same place but all the arrows reverse — the field becomes anticlockwise.
Question 2 · 2 marks
Looking in at the left-hand end of a solenoid, the current flows anticlockwise. Which end of the solenoid is the north pole? Explain how you know.
The left-hand end is the north pole, because anticlockwise = N when you look in at that end. (The right-hand end is therefore the south pole, and looking in at it the current would appear clockwise.)
Question 3 · 4 marks
A student builds an electromagnet from a coil of wire, a cell and a steel nail. It is too weak, and it stays slightly magnetic after the switch is opened. Suggest two changes that would make it stronger, and explain the change you would make to the nail.
Stronger: increase the current and add more turns to the coil (either, plus a soft iron core, gains the marks). The nail should be soft iron, not steel: steel is a magnetically hard material, so it stays magnetised after the current stops, while soft iron loses its magnetism immediately — so the electromagnet switches fully off.
📘 Workbook pages — on their way
The Section 6 pages of the Edexcel International GCSE workbook are being written: the two field patterns to sketch and label, and exam-style questions with worked answers.
Edexcel iGCSE Physics Workbook · Section 6 · coming soonUntil then, sketch both patterns from the animation above — the ⊙ / ⊗ view of the wire, and the solenoid with its arrows — and check them against the notes.
✅ Can you do it? Tick as you go
0% complete🎉 Nice work! You've ticked off every objective for this spec point.
Don't forget to hit “Mark complete” at the bottom of the lesson.
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Prefer to watch? Here's the whole thing
Video walkthrough — coming soon
Everything above, explained out loud — useful for a last-minute recap, or if you'd rather hear it than read it.
Everything above, explained out loud — useful for a last-minute recap, or if you'd rather hear it than read it. The video is on its way.
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Video coming soon
The walkthrough for this lesson is being filmed and will appear right here. Until then, the animation and the notes above cover every mark.
Now test yourself
Close the notes and draw both patterns from memory: the wire seen from above, and the solenoid from the side. Then open the animation again and check every arrow points the right way round.
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