BCIT Physics Department

Demonstration Manual

Sound and Wave Motion

DVW15 - Sound Transmission in Vacuum


- To show that sound waves require a medium for transmission.



As the Bell jar is evacuated, the amplified sound dies away rapidly to nil.

If the air is then re-admitted slowly, the sound gradually returns, to its original level.


Use a frequency of about 700 Hz, due to transducer behaviour. Also, use fairly high gain setting on amplifier, and a low gain setting on signal generator.

youtube logo   Watch a bell jar experiment - sound needs medium for propagation video demonstration on Youtube

- Video Created at the Rajesh Physics Center.