Sound Wave
Light, Sound and Waves

Showing sounds on an oscilloscope

Teaching Guidance for 11-14 Supporting Physics Teaching

Sounds on an oscilloscope

Thinking about the teaching

It's great fun to connect a microphone to an oscilloscope and to use the scope to monitor different sounds. Can you sing a perfect note? However, this exercise can be misleading on more than one account.

First, if the time-base of the oscilloscope is turned on, the trace on the screen will look exactly like the crests and troughs of a transverse wave, but the sound wave is a longitudinal wave.

Second, it is very tempting to point out the trace on the screen and to identify wavelength (as the distance between the adjacent crests). This would be wrong because the horizontal axis of the oscilloscope provides a measure of time.

The best way around these problems is to switch the time-base off and see the sound represented as a vertical line on the screen.

Teacher Tip: Using an oscilloscope thoughtfully is essential to not misleading pupils. There is a case for using a computer program to represent the sound more naturally – that is representing amplitude and frequency in as unambiguous a way as possible.

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