Sounds meeting detectors

What the Activity is for

Investigating detectors and describing the process of detection.

This activity focuses on the design of devices to detect sounds. The structure of the ear is important here, but you will also want to be able to refer to microphones, as these transform the vibrations of the air into electrical vibrations.

What to Prepare

• a model ear or a good clear diagram
• a microphone, linked to an oscilloscope with the time-base turned off (as an alternative you might use a computer running sound-analysing software)
• a carefully chosen, large microphone opened up to show the parts

What Happens During this Activity

Lead the class through a discussion whilst looking at the model ear, or at any sound sensing system, to draw out the way in which the to and fro motion of the medium is picked up by the detector. You should also point out that the brain works through processing electrical signals, and that's why ears have to perform this transforming action (from vibrations of the air to changing electrical signals in the brain). Microphones perform exactly the same transformation.

Connecting the microphone to the oscilloscope or computer will give a large-scale, clear representation of the vibration as a vertical trace on the screen. The vertical trace is produced on the oscilloscope by turning the time base off. We strongly recommend that you do not turn the time base on, as explaining the resulting wave-like pattern is likely to lead pupils' thinking down the wrong tracks. It is better to keep things simple and to make the link: from the vibration of the sound to the vibration of the microphone diaphragm to the up and down vibration of the spot on the oscilloscope (producing the vertical line).