>
Home · IGCSE 0625 · Electricity and magnetism · The motor effect · Practice
Core · Practice questions · The motor effect

The force on a wire.

Six original Cambridge-style questions on the motor effect: the demonstration, reversing the current and the field, making the force bigger, the right-angle rule, and the left-hand rule for Extended.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
What the examiner wants

Force, reversal, size.

01
Experiment
[3 marks]

Describe a simple experiment to show that a force acts on a wire carrying a current in a magnetic field.

  • Place a wire between the poles of a magnet, at right angles to the field. ✓
  • Pass a current through the wire. ✓
  • The wire is pushed (it moves), showing a force acts on it. ✓
02
Recall
[2 marks]

State two changes that would increase the size of the force on the wire.

  • Increase the current. ✓
  • Use a stronger magnet (a stronger field). ✓
03
Application
[2 marks]

A wire is pushed to the left when a current flows. State two separate changes, each of which on its own would make the wire push to the right instead.

  • Reverse the direction of the current. ✓
  • Reverse the magnetic field by swapping the magnet poles. ✓
04
Analysis
[2 marks]

A wire carrying a current is placed so that it lies along the direction of the magnetic field. State the size of the force on the wire and explain your answer.

  • The force is zero. ✓
  • The force is largest when the wire is at right angles to the field, and zero when it lies along the field. ✓
05
Application
[2 marks]

Explain how the motor effect is used in a loudspeaker to produce sound.

  • A changing current from the music passes through a coil in a magnetic field. ✓
  • The force on the coil pushes it back and forth, moving the cone and making sound waves. ✓
06
Extended
[2 marks]

Extended: In a motor-effect demonstration the magnetic field points from left to right and the current in the wire flows out of the page towards you. Use the left-hand rule to state the direction of the force on the wire.

  • First finger right (field), second finger out of the page (current). ✓
  • The thumb points upward, so the force on the wire is upward. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.