PhysicsLAB AP Free Response Question
2004 Form B - B3

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A vibrating tuning fork is held above a column of air, as shown in the diagrams above. The reservoir is raised and lowered to change the water level, and thus the length of the column of air. The shortest length of air column that produces a resonance is L1 = 0.25 m, and the next resonance is heard when the air column is L2 = 0.80 m long. The speed of sound in air at 20°C is 343 m/sec and the speed of sound in water is 1490 m/sec.
 (a) Calculate the wavelength of the standing sound wave produced by this tuning fork.

 (b) Calculate the frequency of the tuning fork that produces the standing wave, assuming the air is at 20°C.

 (c) Calculate the wavelength of the sound waves produced by this tuning fork in the water.

 (d) The water level is lowered again until a third resonance is heard. Calculate the length L3 of the air column that produces this third resonance.

 (e) The student performing this experiment determines that the temperature of the room is actually slightly higher than 20°C. Is the calculation of the frequency in part (b) too high, too low, or still correct? Justify your answer.

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