Describe an activity to show that sound needs a medium to travel with a neat well-labeled sketch.
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Sound is a mechanical wave that needs a material to travel. It can travel through the air, water, steel, etc. but cannot travel through a vacuum.
This can be demonstrated by the bell jar experiment.
Suspend an electric bell inside a glass bell jar bypassing the connecting wires through an air-tight cork fitted at the mouth of the jar.
Place the jar over a disc that has a pipe connected to a vacuum pump.
When we turn on the switch, we hear the sound of the bell.
Now, with the help of a vacuum pump, we pump out the air from the jar. The sound becomes fainter.
When most of the air has been removed, we hear a very feeble sound. When there is air inside the jar, sound travels through it to the wall of the jar. This makes the wall vibrate which in turn, sends sound to us.
When air is removed, sound from the bell cannot travel to the wall of the jar.
Therefore, we can see that the sound waves need a material medium for propagation.