Objective

In this lab you will determine experimentally the speed at which sound travels in air (at room temperature).

Reference

Serway & Faughn's College Physics, Chapter 15

Serway's Physics for Scientists & Engineers, Chapter 17

Apparatus

Sound wave Resonance tube (on back counter), and 2 tuning forks, (select two between 300 Hz and 2000 Hz), and striker(cab 4B), Thermometer (cab 4D), Vernier Caliper (cab 5B).

Theory

The frequency of these tuning forks is extremely accurate, and will remain so as long as you guys don't go around banging them on everything, and remains fixed over a fairly large range of

temperatures. The wave length, however, varies with temperature, and since the speed of sound, v = f l, so does the speed of sound. In this experiment you will treat the frequency of a tuning fork as fixed, obtain the length of l experimentally, and use it to calculate the speed of sound v. The sound generated by striking the tuning fork over the hollow tube will be noticeably amplified when the length of the tube equals an odd multiple of l/4. You will measure the length at which the first and third harmonics occur,

L = l/4, and L = 3l/4, and use these to calculate the wave length l at current room temperature, then use this together with the frequency stamped on the fork to calculate the speed of sound v = fl.

Procedure

Part I. Finding the Speed of Sound Using First Tuning Fork.

1. Select a tuning fork, note and record the frequency stamped on it as f1.

2. Obtain a ballpark figure for the wavelength l of this tuning fork by using the value of fA stamped on the tuning fork, and V = 340 m/s. Record this as lbp. Estimate the value of L1 using L1 = lbp/4.

3. Set the apparatus so that the water level is about 4 cm above the estimated L1.

4. Pinch the tube and lower the can well below your estimate for L1.

5. Strike the fork and release the tube allowing the water level to fall slowly until the sound reaches the first maximum level. Record this length as L11 for trial 1 and repeat the experiment two more times, record these results as L12 and L13 for trial 2 and 3, compute and record the average value L1.

6. Calculate l11 = 4L1.

7. Estimate the second length L2 at which resonance occurs using L2 = 3l11/4. Set the water level about 4 cm above this mark and obtain the actual value of L2 using the same procedure used in steps 4 and 5 above to obtain L1.

8. Calculate l12 = 4L2/3.

9. Now calculate and record l1 = (l11 + l12)/2.

Calculate and record V1 = f1.l1 on your data sheet.

Part II. Finding the Speed of Sound Using Second Tuning Fork.

Select another tuning fork and repeat steps 1 thru 10 in Part I to find l2 and V2.

Part III. CALCULATIONS.

Find the average (V1 + V2)/2 = Vexp and record on data sheet.

2. Obtain room temperature T using a thermometer and record.

3. Calculate the speed of sound at this temperature using the formula

Vcal = (332 + .6 T) m/s.

(T is in centigrade degrees)

4. Find the percent error of the experimental value of the speed of sound (using Vcal in the denominator of your formula as the correct value).

Questions:

1. Find the radius of the resonance tube.

2. Using Vcal and the frequency stamped on the first tuning fork, calculate the correct value of the wavelength of the first tuning fork you used, obtain LA, the value your L1 = l/4 should have been for that first part of the experiment. Assuming that the correction which needs to be added to L1 to make it equal to LA is simply proportional to the radius of the tube, calculate the value of this correction in terms of the radius r of the hollow tube.

(In other words, find the equation LA = L1 + kr. (your main job is to find k.))

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