Brainlag PlusHow a loudspeaker uses the motor effect, then the reverse: moving a magnet and a coil induces a potential difference, what makes it bigger, and which way the current flows.
The loudspeaker
A loudspeaker is the motor effect at work.
A light cone is fixed to a coil that sits in the field of a permanent magnet.
- The amplifier sends an alternating current through the coil
- The coil is in a magnetic field, so it feels a force
- Each time the current reverses, the force reverses: the coil moves in, then out
- The cone moves with it and pushes the air: pressure waves, which we hear as sound
The cone vibrates at the frequency of the current, so a higher frequency gives a higher pitch, and a bigger current gives bigger vibrations: a louder sound. Headphones are tiny loudspeakers.
The rest of this lesson and its 9 practice questions are in Plus.
Screen 1 of 4, free to read.
- 9 exam-style questions, marked as you go, each with a worked solution
- Anything you get wrong is saved to your flashcards