Physics Project 2010

Study of Striations with Kundt's Tube

Faculty Mentor - Drs. Thomas Meyer, Vladimir Gasparayan

Kundt's Tube Apparatus consists of a 90 cm long, 1 in diameter glass tube and an 81 cm aluminum rod. The rod is clamped at its center, while about 10 cm of it extends into the glass tube. A ¾ in disk is attached to the end of the rod to serve as a piston and effectively close off the tube, the other end being closed by a stopper. When the free end of the aluminum rod is stroked with a piece of rosined leather, a high pitched sound is produced by the vibration of the other and freely swinging end of the rod. This in turn produces standing waves in the air of the glass tube. When a thin layer of cork dust is placed in the tube, the dust collects in heaps indicating the nodes and antinodes of a standing wave produced in the tube. The distance between the nodes and the known speed of sound in air allow the measurement of the speed of sound in aluminum. During the previous Chevron REVS-UP programs, Dr. Gasparyan, Dr. Meyer and teams of high school students and teachers also observed striations or fingerlike extensions from the cork dust (see below).

Replacing the rod with the diaphragm of a loudspeaker driven by a sine wave generator and an amplifier allows us to vary the amplitude and frequency of the standing waves in the tube. Last year we continued the study the striations as a function of frequency and various types and sizes of tubes. Within the accuracy of our measurements, the distance between the striations was quite the same under all these conditions and did not differ as a function of frequency and amplitude of the acoustic waves.

To make a more detailed study and more accurate measurements of the distance between the striations, which is of order 2 -3 mm, we observed the effect through a microscope and took high speed movies to watch the movement of individual dust grains. A movie, summarizing some of our observations, can be viewed at www.csub.edu/~tmeyer.

We plan to continue our studies in several directions. First of all, we would like to increase the frequency range, which is at present limited by the response of our loudspeaker to about 400 - 4,000 Hz. We are particularly interested in observing the striations at higher frequencies, when the wave length of the acoustic wave is of the same magnitude as the observed distance between striations. We also would like to investigate the question, if striations can be formed in a liquid medium, such as water.

In addition, our program will continue to develop experiments and demonstrations appropriate for high schools and middle schools, which then could be taken back to the schools by participating teachers. All projects will be open-ended, i.e. participants will be able to work on the projects and develop new ones as they obtain results. Or they will be able to improve on the experimental techniques to obtain better results. We will focus on Acoustics, a subject typically not covered in high school or college curricula. All experiments are exploratory, i.e. no specific instructions are given. Participants study the underlying physics, develop the experimental techniques and then design the experiments. Four experiments are proposed:

1. Measure the speed of sound in various gases and under varying conditions (temperature and pressure). We would like to extend these experiments to measure the speed of sound in liquids.
2. Measure the speed of sound in metals using Kundt's tube apparatus.
3. Make a quantitative measurement of the Doppler effect by measuring and analyzing the wave spectrum generated by a rotating sound source and that produced by a moving car.
4. Design an experiment to break a wine glass using sound waves.

We will extend these studies to Optics and Lasers, depending on the number of students in the group and time available. The physics involved, i.e. wave physics, is similar to that of acoustics. This will allow a comprehensive treatment of the theoretical physics required for both programs. We propose two areas of experimentation:

1. Make a high precision measurement of the speed of light using several methods. One will use Fizeau's rotating mirror experiment and the other will use electronic techniques to measure the speed of light pulses in a coaxial cable and in a plastic light guide.
2. Use of interferometry (Michelson, Fabry-Perot, Twyman-Green) to measure the index of refraction of air as a function of gas pressure and temperature, the index of refraction of glass, and to study distortion in optical components such as lenses.