PURPOSE: To demonstrate the effect of frequency on diffraction of sound.

DESCRIPTION: The collimator is aimed and rotated through the class. For low frequencies (long wavelengths) there is lots of diffraction, and very little collimation is observable. For high frequencies (short wavelengths) there is substantially less diffraction, and the sound is significantly louder when the collimator is aimed at the observer. Good frequencies are about 120Hz and 4000 Hz.

SUGGESTIONS:

See Question of the Week #143 for information on using this demonstration to enhance class involvement.

REFERENCES: (PIRA unknown.)

EQUIPMENT: Sound collimator with oscillator.

SETUP TIME: None.