Unit 10
Waves & Wave Properties
Determining the
Speed of Sound Lab
Purpose: To determine the speed of sound by
measuring the wavelength and frequency of
several tuning forks.
•A sound wave will be produced by a
tuning fork and that wave will be
reflected by the water boundary.
•After reflecting it will interfere and
create a standing wave in the
column.
Antinode = highest amplitude = loudest sound!
Node = No amplitude = no sound!
• Wave speed is product of a wave’s frequency
and wavelength.
– The frequency of the wave is given for each tuning fork.
• To determine the speed of sound the
wavelength must be measured.
•By listening for the 1st loudest
point you will fit the first
antinode.
•This distance is ¼ of the total
wavelength.
Background Information
• Which equation(s) can be used for solve for the speed of sound?
• What variable(s) are known? How?
• What variable(s) can be measured? How?
• What does the accepted speed of sound depend on?
• What is the equation will be used to solve for the accepted
speed of sound?
• Predict: What wave properties will change when for the
different frequency tuning forks? What wave properties will stay
the same?
Background Information
• Which equation(s) can be used for solve for the speed of sound?
Wave speed is product of a wave’s frequency and wavelength. v = f λ
• What variable(s) are known? How?
Frequency (f) - it is written on each tuning fork.
• What variable(s) can be measured? How?
Wavelength (λ) – by finding the length of the wave when the sound is the
loudest (the antinode) which represents ¼ of the wave! λ = 4 x length
• What does the accepted speed of sound depend on?
The medium the wave travels through – in this case “air” (gas). But
temperature and humidity can affect the speed of sound in air.
• What is the equation will be used to solve for the accepted speed
of sound? Vaccepted= 331m/s + (0.6m/s x room temperature)
• Predict: What wave properties will change when for the different
frequency tuning forks? What wave properties will stay the same?
The change frequency will change the wavelength of the wave.
The change in frequency will NOT change the speed of sound.
Procedure:
1.
2.
Set up the velocity of sound apparatus as directed.
Obtain three different tuning forks and record the frequency of each on
your data table.
3. Strike one of the tuning forks with the rubber mallet. (Never strike a
tuning fork on a hard surface.)
4. While the tuning fork is ringing bring the prongs to the top of the pipe.
5. Slowly raise the white tube out of the water while you are holding the
vibrating fork near the open end of the tube. At one point you will hear a
sharp increase in the volume created by the tuning fork. This point
indicates the position of the first node.
6. Notice this point, strike the tuning fork again and carefully adjust the
height of the tube so that the sound is its loudest.
7. Record in meters as “Length”
8. Repeat for each of the remaining two tuning forks.
9. Obtain the exact classroom temperature (oC) and record.
10. Return all materials.
Data & Calculations Table:
Tuning
Fork
Frequency (Hz)
f
Length (m)
Wavelength (m)
λ
Velocity (m/s)
Vexp
Accepted Speed
of Sound
Vacc
Percent
Error
1
2
3
Temperature
of Classroom
oC
Average
Experimental Speed
of Sound
Vavg
Calculations: Show all work!
1. Wavelength λ
(λ = 4 x Length)
2. Speed of Sound Vexperimental (Vexp= f λ)
3. Average Experimental Speed of Sound
Vexperimental (avg) Vavg =[Vexp1+ Vexp2+ Vexp3]/3
4. Accepted Speed of Sound Vaccepted
Vaccepted= 331m/s + (0.6m/s x room temperature)
5. Percent error
%error = ‫׀‬Vexperimental(avg) – Vaccepted ‫׀‬x 100
Vaccepted
Conclusion Questions:
1. What was the average speed of sound for all three tuning forks?
2.
What factor changes when the frequency of the sound wave
changes? (A.E.S.)
3.
Compare the speeds of sound for each of the different frequencies;
does the speed of sound change when the frequency of the sound
changes or does it stay approximately constant? (A.E.S.)
(“E” is” the only way to change the speed of sound is to…”)
4.
The accepted speed of sound and the experimental speed of sound
should match perfectly, but they do not.
a) What is the accepted speed of sound?
b) What is the percent error? Explain some sources of error that
1. What was the average speed of sound for all three
tuning forks?
2. What factor changes when the frequency of the
sound wave changes? (A.E.S.)
3.
Compare the speeds of sound for each of the different frequencies;
does the speed of sound change when the frequency of the sound
changes or does it stay approximately constant? (A.E.S.)
(“E” is” the only way to change the speed of sound is to…”)
4.
The accepted speed of sound and the experimental speed of sound should
match perfectly, but they do not.
a) What is the accepted speed of sound?
b) What is the percent error? Explain some sources of error that occurred in
this lab.
Find the Speed of Sound for the sound wave
each tuning fork creates.
Frequency (f) Hz
600
300
Wavelength (λ) m
0.600
1.20
Velocity (V) m/s
360
360
1. Does the frequency change the speed of sound? (Use data to support)
No, a change in frequency does not change the speed of sound. The speed of sound
only changes if the medium changes. For both frequencies of 600Hz and 300Hz the
speed of sound remained constant, 360m/s.
2. What does change when the frequency changes? (Use data to support)
A change in frequency changes the wavelength. Frequency and wavelength are inversely
proportional. When the frequency decreases the wavelength increases. For example, a
frequency of 600hz has a small wavelength of 0.600m. But if the frequency decreases to
300Hz, the wavelength increases to 1.20m.
3. What is the only way to change the speed of sound?
Changing the medium
4. The speed of sound in 25oC air is 346m/s. According to your answer for the speed of
sound above, do you think this room the lab was completed in was hotter or colder
than 25oC? Hotter, because the speed is faster than 346m/s, sound moves faster in
a hotter medium.