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Investigating Sound as a Wave


Simple model to help show that sound travels in waves.


This is a simple but effective demonstration which shows students that sound waves can be reflected like other waves.

This practical involves taking a ticking wrist or fob watch and placing it into a large gas jar or thick walled tube. By placing the ear directly over the tube, you should be able to clearly hear the ticking but placing the ear at right angle to the top of the tube, the sound should be quieter or not heard at all. By holding a 'reflector' – a piece of glass or other hard smooth material at a 45° angle to the top of the tube and placing the ear at a right angle should result in hearing the ticking once again. The sound wave has been reflected just like a light beam would if the material was a mirror.

The sound wave follows the 'Law of Reflection' where the angle if incidence equals the angle of reflection therefore if the wave hits the reflector at 45°, the reflection leaves the surface at 45° too.

Testing this rule, students can use two tubes angled towards a hard smooth surface and try different angles of incidence. With a ticking watch in one of the tubes and an ear at the end of the other, they should find that they can only hear the ticking when both of the tubes are at the same angle to the reflector.


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