Loudspeakers & Headphones (AQA GCSE Physics)
Revision Note
Loudspeakers & Headphones
Higher Tier Only
Loudspeakers and headphones convert electrical signals into sound
They work due to the motor effect
A loudspeaker consists of a coil of wire which is wrapped around one pole of a permanent magnet
Diagram showing a cross-section of a loudspeaker
An alternating current passes through the coil of the loudspeaker
This creates a changing magnetic field around the coil
As the current is constantly changing direction, the direction of the magnetic field will be constantly changing
The magnetic field produced around the coil interacts with the field from the permanent magnet
The interacting magnetic fields will exert a force on the coil
The direction of the force at any instant can be determined using Fleming’s left-hand rule
As the magnetic field is constantly changing direction, the force exerted on the coil will constantly change direction
This makes the coil oscillate
The oscillating coil causes the speaker cone to oscillate
This makes the air oscillate, creating sound waves
Examiner Tips and Tricks
Microphones and loudspeakers look very similar, but they do very different things. When tackling a question on either of them, make sure you are writing about the right one!
The explanation of the loudspeaker is very similar to the explanation of a motor, however direct current is used in a d.c motor and alternating current is used in a loudspeaker or headphone. You need to learn how both work.
When explaining how a loudspeaker works remember to refer to the alternating current and the changing magnetic field that it creates.
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