Unit 10Waves & 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.

Node = No amplitude = no sound!

Antinode = highest amplitude = loudest sound!

•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.

• 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?

• 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?

Wave speed is product of a wave’s frequency and wavelength. v = f λ

Frequency (f) - it is written on each tuning fork.

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 lengthThe medium the wave travels through – in this case “air” (gas). But temperature and humidity can affect the speed of sound in air.

Vaccepted= 331m/s + (0.6m/s x room temperature)

The change frequency will change the wavelength of the wave.The change in frequency will NOT change the speed of sound.

Procedure:1. Set up the velocity of sound apparatus as directed. 2. 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

1        

2        

3        

Temperatureof Classroom

oC

Average Experimental

Speed of SoundVavg

Accepted Speedof Sound

Vacc

Percent Error

Calculations: Show all work! 1. Wavelength λ (λ = 4 x Length)

3. Average Experimental Speed of Sound Vexperimental (avg) Vavg =[Vexp1+ Vexp2+ Vexp3]/3

5. Percent error %error = ׀Vexperimental(avg) – Vaccepted ׀ x 100

Vaccepted

2. Speed of Sound Vexperimental (Vexp= f λ)

4. Accepted Speed of Sound Vaccepted Vaccepted= 331m/s + (0.6m/s x room temperature)

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

occurred in this lab.

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 Wavelength (λ) m Velocity (V) m/s600 0.600 300 1.20

360

360

1. Does the frequency change the speed of sound? (Use data to support)

2. What does change when the frequency changes? (Use data to support)

3. What is the only way to change the speed of sound?

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?

Changing the medium

Hotter, because the speed is faster than 346m/s, sound moves faster in a hotter medium.

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.

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.