Part B - Problem: How do you measure the velocity of sound using Resonance?

1. Measure the air temperature in the area of the experiment.

2. Predict the length of the tube where resonance will occur.

a. Calculate the velocity of sound using the temperature method.

This velocity of sound is the theoretical value.

VT = 330 m/sec.+ (.6 m/sec. 0C x T)

b. Calculate the wavelength of the sound.

Since V = f x l then l = V f

c. Calculate the length of the column.

Column Length = l 4

3. Measure the length of the tube where resonance will occur.

a. Clamp the 5.00-cm diameter plastic tube in a vertical position on a ring stand.

b. Place a container filled with water to within approximately 2-cm. of the top of the container.

c. Strike the tuning fork on the rubber mat provided causing it to vibrate. The number stamped on the tuning fork (480, 512), is the frequency (f) of the sound.

d. Hold the vibrating tuning fork over the tube as close to the tube as possible. Adjust the position of the tube in the water by raising it or lowering it until the sound from the vibrating tuning fork is intensified. This is the point at which resonance occurs. Clamp the tube so an accurate measurement can be made.

e. Measure the length of the air column in the tube (in meters) from the surface of the water to the top of the tube, (L). The wavelength (l) of the sound is equal to four times the length of the air column.

 

Remember: When a vibrating tuning fork is in 'down' position, the sound wave travels down the tube, reflect off the water, and returns to the tuning fork, just as it reaches the 'up' position. The reflected sound reinforces the sound made by the tuning fork, making it seem louder. The sound has gone down the length of the tube and back; or 2L, in half of a wavelength. The length of the tube is therefore one-forth the wavelength. To determine the wavelength of the sound produced multiply the length of the tube by four. This relationship can be expressed as:

l = 4 x L (Record this value in meters.)

 

4. The velocity of sound is equal to the product of the wavelength and frequency. VE = f x l. This velocity of sound will be considered the experimental value.

 

5. Compute error/percentage of error using the above values of VE and VT, and record them. If your value for the percentage of error is more than 10%, look closely for errors, and repeat the experiment.

 

6. Repeat steps 1- 5, using a tuning fork with a different frequency, (512).