Turn-in Homework #6 Physics 212 Due Tuesday 11/18/2014

Turn-in Homework #6
Physics 212
Due Tuesday 11/18/2014
1. As a take-home lab exercise, a couple of physics students are measuring the depth of a water well using
sound resonance. They have a function generator, amplifier, and speaker through which they can play
tones between 75.0 Hz to 150.0 Hz. They notice distinct resonances at 91.0 Hz, 117 Hz, and 143 Hz, but
no other frequencies in the 75-150 Hz range cause resonance within the well. Note that a well is
effectively a tube open on one end (the top) and closed at the other end (the bottom, by water usually.)
If the speed of sound in air is 340.0 m/s, what is the depth of the well?
2. You are sitting in a lecture hall where the physics instructor can play a single tone (frequency) through
two speakers. You happen to be sitting in a location where you are 8.75 m from one of the speakers and
6.30 m from the other speaker. The two speakers are in-phase with each other. If the instructor starts at a
low (but still audible) frequency and slowly increases the frequency to higher and higher pitches, what are
the two lowest frequencies for which the volume will be the loudest where you’re sitting? What are the
two lowest frequencies for which the volume will be the quietest? The speed of sound in the air in the
room is 343 m/s; ignore wall, ceiling and floor reflection interference. Assume your ears are equally
responsive to the volume level of all frequencies.