Make-up lab

Sound

Vibrating objects can produce sound.  Sound waves are longitudinal waves.  They can travel through solids, liquids and gases.  In this laboratory you will visualize the patterns of pressure variations associated with different sounds traveling through air and you will examine the frequency content of those patterns.  You will also examine standing sound waves in a tube and measure the speed of sound waves in air.

Open a Microsoft Word document to keep a log of your experimental procedures, results and discussions.  Address the points highlighted in blue.  Answer all questions.


Exercise 1

Produce a sound pulse by clapping your hands once.

Sound is a pressure variation that propagates through a gas or solid. 
Consider a long, gas-filled cylinder with a piston on one end.


image

Note:  While the pressure variation travels down the cylinder, the gas particles do not.  They move back and forth over a relatively small distance.

Sketch pressure in the cylinder as a function of position along the cylinder axis for the figures (a) and (b) to the right.


image

This Word document contains the figures.  Choose insert Shapes Lines, Scribble, and then sketch with the mouse.


Experiment 1

Most sounds we hear are not single sound pulses but more complex sound patterns.  We will now explore some of those sound patterns.

(a)  Compare the output of your computer's microphone for a clapping and a humming sound.  The microphone converts pressure variations into voltage variations which can be recorded and displayed by the computer.

(b)   Examine the output of your computer's microphone for the sound produced by a tuning fork.

(c)  Any wave pattern can be produced by superimposing the appropriate sinusoidal waves.  Breaking up the original sound wave into its sinusoidal components is called Fourier analysis.  We can find the frequencies and amplitudes of the sine and cosine waves that must be added to produce our sound wave by letting the computer perform a Fourier analysis on the sound.


Experiment 2

Watch this Tube Resonance video.

Measure the speed of sound

Assume you had followed the procedure outline below to make measurements using a resonance tube and two tuning forks.  With a magnet you can move a piston inside the resonance tube to adjust its length.  The maximum length is 1 m.  The tube has one open and one closed end.  For a fixed frequency you can produce several resonances by varying the length of the tube.  The closed end of a tube is a node in the longitudinal displacement.  The open end of a tube is approximately an antinode in the longitudinal displacement.

image          image

image

Procedure:

This is the procedure that was followed to obtain the data in table 1.

Table 1

(tube length (m)))

  1st harmonic
L (m)
3rd harmonic
L (m)
5th harmonic
L (m)
frequency
f (Hz)
temperature
o
C
fork 1 0.121 0.353 0.583 741 21
fork 2 0.229 0.678 not found 384 21

Analyze the data and complete table 2. 

The displacement nodes of standing waves in a tube are well defined, while the displacement antinodes at the ends can be displaced by a small distance from the actual ends of the tube.  So it is best to use the distance between antinodes to to find the wavelength λ,

Table 2

  frequency f wavelength λ temperature TC speed v = λf
fork 1        
fork 2        

Compare your experimentally obtained value for the speed of sound with the value obtained from the formula
v = (331.4 + (0.6/oC)TC) m/s.


Convert your log into a lab report.

Name:
E-mail address:

Make-Up Laboratory Report

Save your Word document (your name_mape-up lab.docx), go to Canvas, Assignments, Make-up lab, and submit your document.