WJEC GCSE Physics
WJEC GCSE Physics 1.9 Electromagnetism Exam Questions
Free WJEC GCSE Physics revision for 1.9 Electromagnetism: what you need to know, common mistakes and exam-style questions with answers. Covers magnetic fields, the motor effect, Fleming's left-hand rule, F = BIl, d.c. motors, electromagnetic induction, generators and transformers.
Practise 1.9 Electromagnetism with past papers
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About WJEC GCSE Physics 1.9 Electromagnetism
Electromagnetism closes Unit 1 and links electricity with magnetism. You need to draw field patterns for bar magnets, straight wires and solenoids, explain the motor effect and use Fleming's left-hand rule and F = BIl. You must describe how a simple d.c. motor works and what affects its speed and direction. The topic then covers electromagnetic induction, the a.c. generator and how transformers work, using V1 / V2 = N1 / N2 for an ideal transformer. It connects back to the National Grid in 1.2. Investigating the output of an iron-cored transformer is the specified practical, and examiners often ask for clear explanations of induction.
What you need to know
- Magnetic fields Field lines go from north to south around a bar magnet. A current in a straight wire makes circular field lines around it; a solenoid's field is like a bar magnet's and is strong and uniform inside.
- Motor effect A current-carrying wire in a magnetic field experiences a force. Fleming's left-hand rule: first finger field, second finger current, thumb motion (force). F = BIl when current and field are at right angles.
- d.c. motor Forces on opposite sides of a current-carrying coil act in opposite directions, making the coil rotate. A split-ring commutator reverses the current every half turn. Speed increases with more current, a stronger field or more turns.
- Electromagnetic induction A voltage is induced when a conductor moves relative to a magnetic field or the field through a coil changes. If the circuit is complete, a current flows.
- Generators An a.c. generator rotates a coil in a magnetic field, inducing an alternating voltage. Output increases with faster rotation, a stronger field or more turns.
- Transformers An alternating current in the primary coil creates a changing magnetic field in the iron core, which induces an alternating voltage in the secondary coil. V1 / V2 = N1 / N2. Investigating transformer output is the specified practical.
Common mistakes in 1.9 Electromagnetism
- Using the right hand for the motor effect. Fleming's left-hand rule is for motors; the right-hand rule is used for generators.
- Saying transformers work with d.c. They need alternating current to produce a changing magnetic field; a steady d.c. induces no voltage after switching on.
- Writing that the magnet must be moving to induce a voltage. Any relative movement or change in magnetic field works, including moving the coil.
- Flipping the transformer ratio. If the secondary has fewer turns than the primary, the output voltage is lower (step-down).
Try three 1.9 Electromagnetism exam-style questions
1. A wire 0.05 m long carries a current of 3 A at right angles to a field of 0.2 T. Calculate the force on the wire. (2 marks)
Show the mark scheme answer
F = BIl = 0.2 x 3 x 0.05; = 0.03 N.
2. A transformer has 2000 turns on the primary and 100 turns on the secondary. The input voltage is 230 V. Calculate the output voltage. (2 marks)
Show the mark scheme answer
V2 = 230 x 100 / 2000; = 11.5 V.
3. Explain how a transformer changes the size of an alternating voltage. (4 marks)
Show the mark scheme answer
Alternating current in primary coil; produces a changing magnetic field in the iron core; changing field passes through secondary coil; induces an alternating voltage, whose size depends on the turns ratio.
1.9 Electromagnetism FAQs
What does WJEC GCSE Physics 1.9 Electromagnetism cover?
It covers magnetic field patterns, the motor effect, Fleming's left-hand rule, F = BIl, d.c. motors, electromagnetic induction, a.c. generators and transformers.
Which unit is Electromagnetism examined in?
It is examined in Unit 1: Electricity, Energy and Waves, a 1 hour 45 minute written paper worth 45% of the GCSE, sat at foundation or higher tier. The Unit 3 practical assessment draws on the same practical skills.
How do I use Fleming's left-hand rule?
Hold your thumb, first finger and second finger at right angles: first finger for the field (north to south), second finger for current (positive to negative), and the thumb gives the direction of motion.
