How do magnets and electric currents produce magnetic fields and forces?
Magnetic fields around magnets and current-carrying wires, electromagnets, the motor effect and Fleming's left-hand rule, and the electric motor.
A CCEA GCSE Physics answer on magnetic fields around magnets and current-carrying wires, electromagnets, the motor effect and Fleming's left-hand rule, and how a simple electric motor works.
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What this dot point is asking
CCEA wants you to describe magnetic fields around magnets and current-carrying wires, explain electromagnets, describe the motor effect and use Fleming's left-hand rule, and outline how a simple electric motor works. Field directions and the rule are central.
The answer
Magnetic fields around magnets
The field around a current-carrying wire
When a current flows through a wire, it creates a circular magnetic field around the wire. Coiling the wire into a solenoid concentrates the field, giving a pattern like a bar magnet, with a north and south end.
Electromagnets
The motor effect
The electric motor
In a simple motor, a coil carrying a current sits in a magnetic field. The motor effect pushes one side of the coil up and the other down, making it turn. A split-ring commutator reverses the current every half-turn so the coil keeps spinning in the same direction.
Worked example: a wire in a field
Examples in context
Example 1. A scrapyard crane. An electromagnet lifts cars and scrap iron when switched on and drops them when switched off, something a permanent magnet could never do.
Example 2. A loudspeaker. A current in a coil sitting in a magnetic field feels a varying force (the motor effect), pushing a cone back and forth to make sound waves.
Try this
Q1. State two ways to increase the strength of an electromagnet. [2 marks]
- Cue. Increase the current; add more turns (or use an iron core).
Q2. Which rule gives the direction of the force in the motor effect? [1 mark]
- Cue. Fleming's left-hand rule.
Q3. What is the role of the split-ring commutator in a motor? [2 marks]
- Cue. It reverses the current every half-turn so the coil keeps turning the same way.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA style4 marksDescribe how you could increase the strength of an electromagnet made from a coil of wire around an iron core, giving two methods, and state one use of an electromagnet.Show worked answer →
Two methods to increase the strength: increase the current through the coil; and increase the number of turns on the coil. (Using a soft iron core also strengthens it.)
One use: a scrapyard crane to lift and drop iron and steel (or a relay, an electric bell, or a magnetic door lock).
Markers reward two valid methods to strengthen the electromagnet and one valid use.
CCEA style3 marksA current-carrying wire is placed between the poles of a magnet and experiences a force. State the rule used to find the direction of this force and two ways to increase the size of the force.Show worked answer →
Fleming's left-hand rule gives the direction of the force (the thumb shows the force, the first finger the field, the second finger the current).
Two ways to increase the force: increase the current; and increase the strength of the magnetic field. (Increasing the length of wire in the field also increases it.)
Markers reward Fleming's left-hand rule and two valid ways to increase the force.
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Sources & how we know this
- CCEA GCSE Physics specification — CCEA (2017)