A doctor uses an ultrasound device that contains a loudspeaker to direct sound waves into a patient's body. Explain how the loudspeaker in the device converts an oscillating electrical current into sound waves.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Ultrasound devices used in medicine contain loudspeakers that receive oscillating electrical signals and produce sound waves at frequencies above the range of human hearing.
Model answer (4 marks)
The oscillating electrical current flows through the coil that is attached to the cone or diaphragm. The current in the coil creates a magnetic field that interacts with the permanent magnet in the loudspeaker, producing a magnetic force on the coil. Because the current alternates, the direction of the magnetic force reverses repeatedly, causing the coil and the attached cone to move back and forth. The rapid back‑and‑forth motion of the cone creates alternating compressions and rarefactions in the surrounding medium, which propagate as sound waves.
Examiner tips
- Use the word ‘oscillating’ to link the current to the coil motion; mention the permanent magnet explicitly; describe the force reversal; explain how cone vibration produces sound.
- Show the chain of events in a clear, logical order to hit all four points.
Mark scheme (4 marks)
- The oscillating current passes through the coil (attached to the cone/diaphragm)
- The coil experiences a force due to the interaction between the current and the magnetic field (of the permanent magnet)
- Because the current oscillates, the force on the coil (and cone) reverses repeatedly / the coil moves back and forth
- The vibrating cone causes compressions and rarefactions in the surrounding medium, producing sound waves
Key terms in this question
Related
- All Eduqas GCSE Physics revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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