Demonstration Manual

Sound and Wave Motion

DVW18.1 - Interference Tubes Method II

Objective:

- To show that two sound waves of the same frequency cancel out if one has to travel 1/2 wavelength further than the other.

Apparatus:

• Custom PVC interference tube loop
• Stand, 3-fingered clamp
• Function generator, Wavetek
• Speaker (University Sound model 1D30C-8)
• Banana leads, two
• BNC/Banana adapter

Method:

Set the frequency generator to generate a 2.1 KHz sine wave. Fine tune the frequency control to attain maximum sound output, with the top loop retracted. The sound is split into two paths which re-combine at the output. If the top loop is lengthened by 1/2 wavelength, the two sound waves interfere and very little output is heard.

Note:

The effect can be demonstrated to an entire class at once.

   Watch a Interference Demo: Red-Neck Trombone video demonstration on Youtube

- Video Created at Utah State University by Professor Boyd F. Edwards and assistants.