In this activity, students will hear a dramatic effect of the interference of sound.
Interference is a behavior common to all waves. With water waves we see it in regions of calm where overlapping crests and troughs coincide. We see the effects of interference in the colors of soap bubbles and other thin films where reflection from nearby surfaces puts crests coinciding with troughs. In this activity we'll dramatically experience the effects of interference with sound!
Stereo radio, tape, or CD player with two moveable speakers, one of which has a DPDT (double pole double throw) switch or a means of reversing polarity (such as switching red and black wires).
The "Speakers" required for this lab are available from Radio Shack or can be salvaged from old stereo speaker systems. Each lab group would need access to one of each see lab detail for specific use.