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--- demonstrations:3_oscillations_and_waves:sound_waves:beat_notes:start [2019/01/31 22:58] – demoroom
+++ demonstrations:3_oscillations_and_waves:sound_waves:beat_notes:start [2020/03/06 18:57] (current) – demoroom
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 ====== Beat Notes ======
-{{tag> needs_review untagged unlocated}}
+{{tag> interference acoustics oscillations_and_waves frequency located}}
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 ===== Description =====
-Beating between two frequencies which are close to each other.    Classes Used: PHYS 101, 153, 158
+Demonstration consists of a pair of tuning forks mounted on wooden boxes which are open on one end. One of the tuning forks has a pair of adjustable weights which attach to the forks.
-waves, beats   Updated on: 06/19/13
+This demonstration can alternatively be run using a pair of organ pipes (where one of them is adjustable to be very close to the other). In principle any pair of oscillators that can be adjusted to be close to each other will work for this demonstration.
 ===== Purpose =====
+Demonstration of the constructive and destructive interference ('beating') observed when two nearly identical frequencies are played together. [[https://en.wikipedia.org/wiki/Beat_(acoustics)|Relevant Wikipedia page]]
-To demonstrate the audible beating between two frequencies which are close together.
 ===== Apparatus =====
+  * Pair of tuning forks
+  * (Optional: Vernier Labpro, Microphone, and computer with LoggerPro)
-Pair of organ pipes, two tuning forks, oscillators, or amplifiers and horn speakers
+// Or alternatively://
+  * Pair of organ pipes
 ===== Setup =====
+  * Place the pair of tuning forks with resonance boxes on a table so that the open ends of the boxes face the audience. Now, strike both of the forks with a rubber mallet. If the adjustable fork is damped so that it's frequency is slightly different than the other, beats will be heard.
+  * If you are using a LabPro, attach it to the microphone sensor and a computer with LoggerPro open. Set data collection for a few seconds and display the graph of the beating frequencies
-  *Two organ pipes, one with a variable frequency adjustment are sounded together. By moving the frequency adjustment of one pipe to obtain a frequency close to the other pipe will result with beats.
+  * If you do this with a pair of organ pipes, you will need an assistant. Get your assistant to sound the non-adjustable pipe continuously, and begin sounding the adjustable pipe yourself. Adjust the pipes so that they are sounding nearly the same note, and beats should be heard.
-  *Two identical tuning forks on resonance boxes should be placed on the demonstration bench so that the open ends of the boxes are angled to face the audience. If one fork is now damped slightly with a damping piece attached to it, beats will be heard.
-  *Two oscillators with their own speakers are driven producing two separated notes. Oscillator frequencies can be read off and the frequency of the beats heard matched approximately to the difference in frequency of the two oscillators. Providing the speakers and oscillators are nearly identical, an oscilloscope can be connected to show how close the frequencies are to each other.
 ===== Notes =====
+The frequency of the 'beats' tone that you hear is equal to the difference between the two other frequencies being played. If the frequencies are sufficiently close, you may not hear any beats at all, and if they're too far apart the beats will have a high enough frequency to be heard as a [[wp>combination tone]].
+The basic principle is an extension of superposition.
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-| **Location** | ---- |
+| **Location** | T4 |
 | **Maker** | Unknown |
 | **Current State** | Working |