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, Rigol
- Speaker (University Sound model 1D30C-8)
- Banana leads, two
- BNC/Banana adapter
Method:
Set the frequency generator to 2.1 kHz. Fine-tune the frequency control to achieve maximum sound output, with the top loop retracted. The sound is split into two paths, which recombine 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.
Interference Demo: Red-Neck Trombone
– Video Created at Utah State University by Professor Boyd F. Edwards and assistants.