Demonstration Manual

Sound and Wave Motion

DVW15 - Sound Transmission in Vacuum

Objective:

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

Apparatus:

• Bell jar with speaker and microphone
• Vacuum plate
• Vacuum pump
• Audio generator
• Audio amplifier
• Speaker
• Leads

Method:

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.

Note:

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.

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

- Video Created at the Rajesh Physics Center.