How are magnetism and electricity linked in electromagnets, motors and generators?
Magnetic fields and field lines, the magnetic field around a current-carrying wire and a solenoid, the motor effect, and electromagnetic induction in generators and transformers.
A CCEA GCSE Double Award Science (Physics Unit P2) answer on magnetic fields and field lines, the field around a current-carrying wire and a solenoid, the motor effect, and electromagnetic induction in generators and transformers.
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What this dot point is asking
CCEA Double Award wants you to describe magnetic fields and field lines, the field around a current-carrying wire and a solenoid, the motor effect, and electromagnetic induction in generators and transformers. The "how to strengthen an electromagnet" and "how to increase an induced voltage" questions are common.
Magnetic fields and field lines
Like poles repel and unlike poles attract.
Electromagnetism
An electromagnet can be switched on and off and has its strength easily controlled, unlike a permanent magnet.
The motor effect
Electromagnetic induction
Examples in context
- Example 1. A scrapyard crane
- A large electromagnet lifts cars when switched on and drops them when switched off, using the on-off control that a permanent magnet cannot give.
- Example 2. A bicycle dynamo
- Turning the wheel spins a magnet near a coil, inducing a voltage that powers the lights, a direct use of electromagnetic induction.
- Example 3. A loudspeaker
- A current in a coil in a magnetic field experiences the motor effect, pushing the cone back and forth to make sound.
- Example 4. A transformer on the power grid
- Transformers use electromagnetic induction between two coils to step the voltage up for transmission across the country (which reduces the current and so the energy wasted as heat in the cables) and step it back down to a safe level for homes.
Try this
Q1. Which way do magnetic field lines point outside a magnet? [1 mark]
- Cue. From north to south.
Q2. State two ways to make an electromagnet stronger. [2 marks]
- Cue. Any two of: more current, more turns, an iron core.
Q3. What must happen for a voltage to be induced in a coil? [1 mark]
- Cue. The magnetic field through the coil must change (for example a magnet moving in or out).
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 three ways to increase the strength of an electromagnet made from a coil of wire wrapped around an iron core.Show worked answer →
Any three of the following increase the strength of the electromagnet:
increase the current through the coil;
increase the number of turns on the coil;
use a soft iron core (or a more magnetic core).
Markers reward three valid factors from: more current, more turns, an iron core (bringing the poles closer also accepted).
CCEA-style4 marksExplain how a voltage is induced when a magnet is moved into a coil of wire, and state two ways to increase the induced voltage.Show worked answer →
Moving the magnet changes the magnetic field through the coil, which induces (generates) a voltage across the coil. (If the coil is part of a complete circuit, a current flows.)
Two ways to increase the induced voltage: move the magnet faster, or use more turns on the coil (a stronger magnet also works).
Markers reward the changing magnetic field inducing a voltage, and two valid ways to increase it (faster movement, more turns, stronger magnet).
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Sources & how we know this
- CCEA GCSE Science Double Award specification — CCEA (2017)