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AQA 6.7 / PHYSICS

Magnetism and electromagnetism

Why does a compass turn, how can a coil lift steel, and what makes an electric motor spin? Follow the fields, test the evidence and build clear explanations.

Supported GCSE version · Clear examples, worked calculations and optional challenges.

Foundation & Higher30 main + 4 challenge questionsSave and return any time

Understand the science

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YOUR TOPIC GUIDE

Magnetism and electromagnetism

Work through one section at a time. Higher-only material is labelled explicitly; optional challenges can also use Foundation content.

Words to know

Pole

An end of a magnet where its magnetic force is strongest.

Permanent magnet

A magnet that produces its own magnetic field and retains its magnetism.

Induced magnet

A material that becomes magnetised in another magnetic field.

Magnetic field

A region where a magnet or magnetic material experiences a magnetic force.

Uniform field

A field with the same strength and direction throughout a region.

Solenoid

A long coil of wire that produces a magnetic field when current flows.

Electromagnet

A solenoid with an iron core; its magnetism can be controlled by the current.

Conventional current

The direction positive charge would flow; opposite to electron flow in a wire.

Motor effect

The force produced when a current-carrying conductor is in a magnetic field. Higher-only here.

Magnetic flux density

A measure of magnetic field strength, symbol B, measured in tesla. Higher-only here.

Perpendicular

At right angles: an angle of 90°.

Turning effect

The effect of a force that makes an object rotate about an axis.

1. Poles: where magnetic forces are strongest

A magnet can pull or push another magnet without touching it. This is a non-contact force. The strongest forces act near its two ends, called poles.

Poles facing each otherWhat happens?
North and southAttract: pull together
North and north, or south and southRepel: push apart
Two pairs of bar magnets with force arrows showing unlike poles attracting and like poles repelling.
Read the letters on the facing ends. These arrows show force, not field direction.
Repulsion is useful evidence that an object is a magnet. Attraction alone could mean the object is an unmagnetised magnetic material.

2. Permanent magnets and temporary magnets

Permanent magnetInduced magnet
Produces its own magnetic field.Becomes magnetised when placed in another magnetic field.
Keeps its magnetism after the other magnet is removed.Usually loses most or all of its magnetism quickly when the field is removed.
A north pole near an iron bar induces a south pole at the near end and a north pole at the far end.
The near end becomes the opposite pole, so induced magnetism produces attraction.

Magnetic materials include iron, steel, cobalt and nickel. Not all metals are magnetic: aluminium and copper are not attracted strongly by an ordinary school magnet.

Soft iron makes a useful temporary core. It is magnetised easily and loses most of that magnetism when the current is switched off.

3. Field lines show direction and strength

A magnetic field is a region where a magnet or magnetic material experiences a magnetic force. Field lines are a model: there are no visible lines floating in the air.

Curved magnetic field lines outside a bar magnet run from north to south and return south to north inside.
The pattern is three-dimensional; this is a flat slice. Lines closer together represent a stronger field.
  • Direction: the direction a small north pole would be pushed. Outside the magnet, arrows go from N to S.
  • Strength: strongest near the poles, weaker further away.
  • No crossing: the field has one direction at each point.

4. Use a compass to map a field

A compass needle is a tiny bar magnet. Its north-seeking end points along the magnetic field at its position.

Successive compass positions above a bar magnet, with north-seeking tips showing the local field direction.
Each position gives one small part of the field line; use many positions for a smooth curve.
  1. Put a bar magnet on paper and draw around it. Label N and S.
  2. Place a small plotting compass near one pole. Mark both ends of its needle.
  3. Move the compass so its tail sits on the previous north-tip mark. Mark the new tip.
  4. Repeat. Join the marks with a smooth curve and add direction arrows.
  5. Start elsewhere and repeat to build up the pattern.

Earth also has a magnetic field. A compass aligning even when no bar magnet is nearby is evidence for this field and a magnetic source within Earth’s core. The core is not a simple solid bar magnet.

5. Current makes a magnetic field

A current in a wire produces a magnetic field around it. Place a compass near a wire and switch a low-voltage current on: the needle turns. Reverse the current and its deflection reverses.

Concentric anticlockwise magnetic field lines around a wire carrying conventional current out of the page.
A dot is the tip of an arrow coming towards you; a cross is the tail moving away.
ChangeEffect
Increase the currentStronger field
Move further from the wireWeaker field
Reverse the currentReverse the field direction
Right-hand grip rule: point your right thumb along conventional current. Your curled fingers show the circular field direction. This is different from the left-hand motor rule later.

6. Coil the wire to strengthen the field

A solenoid is a long coil of wire. The fields from its turns add together. Inside a long solenoid, the field is strong and approximately uniform: it has similar strength and direction across that region.

A solenoid with an iron core, a south end at left and north end at right, with parallel field lines inside and returning external loops.
Parallel, evenly spaced lines show the uniform field inside. The outside pattern resembles a bar magnet.
  • Increase current to strengthen the field.
  • Use more turns in the same coil length to strengthen the field.
  • Add an iron core to strengthen the field further.
  • Reverse current to swap the north and south ends.

An electromagnet is a solenoid with an iron core. It can be switched on and off, for example to lift and release steel in a scrapyard.

7. Investigate fairly: current and lifting strength

Paper clips give a simple way to compare lifting strength. They do not directly measure magnetic flux density in tesla.

An iron-core electromagnet connected in series with a low-voltage supply and ammeter; paper clips are collected below the core.
Adjust the supply to change current. Use the ammeter reading, not just the supply setting.
VariableExample
ChangeCurrent through the coil
MeasureNumber of identical clips lifted
Keep the sameCore, turns, lifting height and clip type
Improve reliabilityRepeat each current and calculate a mean

Switch off between readings and keep within the teacher-approved current limit: the coil can get hot. Compare results over the tested range; do not assume that twice the current always lifts exactly twice as many clips.

There is no separately numbered AQA required practical in this topic, but planning, graph and evaluation questions can still use electromagnet investigations.

8. Higher only: a current can produce movement

A current-carrying wire in a magnetic field experiences a force. The magnet experiences an opposite force too. This interaction is the motor effect.

Field to the right, current out of the page and force upwards: three perpendicular directions.
Use conventional current. Practise arranging your own left hand; the diagram gives the three directions.
Left-hand digitWhat it represents
First fingerMagnetic field, N to S
Second fingerConventional current, positive to negative
ThumbForce or movement

Hold the three digits at right angles. A stronger field, larger current or longer wire within the field gives a larger force. The force is greatest when the current is perpendicular to the field; a wire parallel to the field has no motor-effect force.

9. Higher only: calculate the force

For a wire perpendicular to a uniform magnetic field:
F = B × I × l
QuantityUnit
Force Fnewton, N
Magnetic flux density B (field strength)tesla, T
Current Iampere, A
Length of wire in the field lmetre, m

Worked example

  1. A 12 cm wire carries 3.0 A at right angles to a 0.40 T field.
  2. Convert first: 12 cm = 0.12 m.
  3. Substitute: F = 0.40 × 3.0 × 0.12.
  4. Answer: 0.144 N.

Rearrange for another quantity: B = F ÷ (I × l), I = F ÷ (B × l), or l = F ÷ (B × I). Only count the wire length actually inside the field.

A straight-line graph of force against current at fixed wire length and field strength.
A line through the origin shows direct proportion. This graph is used again in the practice questions; read its axes carefully.

10. Higher only: make a coil rotate

A rectangular coil has opposite current directions in its two opposite sides. In the same magnetic field, these sides experience forces in opposite directions.

End-on view of a motor coil: field rightwards, left-side current outwards with force up and right-side current inwards with force down.
The separated forces turn the coil about its axis. They do not simply move the whole coil upwards.
  1. Current flows through the coil.
  2. The field interacts with the current and produces opposite forces on opposite sides.
  3. These forces create a turning effect, so the coil rotates.
How can a simple d.c. motor keep turning?

A split-ring contact reverses current in the coil every half-turn. The forces on the two physical sides reverse at the right time, maintaining rotation in one direction. Brushes maintain electrical contact with the rotating ring.

For Trilogy, focus on explaining rotation using forces on the current-carrying coil. Generator effect, transformers and loudspeakers are not part of this topic’s Trilogy requirements.