02 Mar, 2013
PRESENTATION: A pulse is a phenomenon generated by the superposition (interference) of two acoustic waves, each with a frequency that is different from the other’s but very close to it. A familiar example are the pulses produced by sound waves coming from two tuning forks with frequencies that are almost the same but not identical. The outcome is a note or tone whose intensity varies back and forth between a high intensity value (loud volume) and a low-intensity value (quiet volume).
- Analyzing acoustic phenomena with a smartphone microphone, Jochen Kuhn and Patrik Vogt, Phys. Teach. 51, 118 (2013)
- Acoustic Resonators, Thomas B. Greenslade, Phys. Teach. 50, 485 (2012)
INTRODUCTION: The study of waves, in all their forms, is one of the most complex and yet appealing in Physics. Both in current subatomic models and in data transmission, which is vital for modern day life, waves play a fundamental role. The tuning fork is an instrument that has been designed with certain characteristics so that it emits and propagates an oscillatory movement, which is transmitted as a harmonic sound wave, with one fundamental tone.
OBJECTIVE: To analyse the interferences of a certain group of waves, mechanical ones, and their characteristics.
MATERIALS: two tuning forks mounted onto a sound board, two clamps to vary the frequency of the sound emitted by the tuning forks, a rubber hammer.
SETUP: Each tuning fork is placed on its sound board. The clamps are used to change the frequency of the sound emitted by the tuning forks when they are hit by a hammer.
EXPLANATION: Two harmonic sound waves of equal or different frequency that propagate in the same medium will give rise to a resulting wave, also harmonic, whose amplitude depends on the gap between the original waves. This phenomenon is called interference and can be constructive or destructive. In the region of space where two waves interfere, the amplitude of the resulting wave is greater at certain points (constructive interference) and smaller at other points (destructive interference), and it can even be null at those points where the amplitudes of the interfering waves are equal and opposite. If the frequencies of the interfering waves are very similar, a pulse is produced: the amplitude of the resulting wave varies alternatively between a maximum value and a minimum one, and the frequency of variation of the amplitude, that is, the frequency of the pulse, depends on how similar the frequencies of the interfering waves are, and will be null if they are the same. These concepts can be used for tuning instruments: the pulse disappears when the frequency of the note being tuned coincides with the wave it is being compared to.
CONCEPTS: acoustic wave, interference, pulse.
- Tipler P.A. Física, Reverté, 2010.
- De Juana J.M., Física General, Pearson, 2009.
- Serway R.A y J.W.Jewett. Física, Thomson-Paraninfo, 2010.
- R. Ehrlich, Turning the World Inside Out and 174 Other Simple Physics Demonstrations, Princeton University Press, 1997.
STUDENTS 2011-2012: Alejandro Andreu, Damián Baleato, André Bernal, Jonathan Blanco
LINK pdf STUDENTS (in Spanish):