Speaker

Another device which uses the magnetic forces existing on current carrying wires is the speaker. A speaker is a device which takes an electrical signal (which was at one time a sound wave), and converts it back into a sound wave. A basic speaker is pictured below.

  

Figure 9.9: Basic speaker / microphone

In the speaker, electrical signals in the form of an AC current are sent through a loop which is immersed in a magnetic field. This loop thus experiences a force, which is is transferred to the attached speaker membrane. Because the current is alternating, the speaker membrane is alternatively pushed to the left and then to the right in the figure. These vibrations cause air molecules to start to vibrate, which causes a sound wave to be generated, which our ears interpret as sound. By modulating the strength and frequency of the current, it is possible to change the amplitude and frequency of oscillation of the speaker membrane. This results in a corresponding change in the volume, and pitch of the resulting sound.