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Experiment_12 - Lab#12 Waves Purpose a To explore the...

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1 Lab #12 Waves Purpose: a) To explore the formation of standing waves in a vibrating string, and to use experimentally gathered data to determine the string’s mass per unit length. b) To explore the phenomenon of resonance, and to use experimentally measured data to determine the speed of sound in air. Equipment: Vibrating string apparatus Resonance column apparatus Hanger and weights Tuning forks Graph Paper Barometer & Thermometer Strobe light for demonstrations Discussion: (General) Waves may be divided into one of two categories: transverse waves or longitudinal waves. Transverse waves are those in which the particles in the wave medium move PERPENDICULAR to the direction of propagation of the wave itself. An example is seen after a stone is tossed into a quiet pond. The wave travels outward in an expanding circular shape, and its motion is visibly horizontal. But we can see from the motion of a waterbug or leaf on the surface that the motion of the water particles themselves as the wave passes by is vertical. Longitude waves are those in which the particles in the wave medium move in the SAME DIRECTION as the direction of propagation of the wave itself. An example may be seen in the toy spring known as “slinky”. Suppose it is stretched along the floor between two people. If one person suddenly compressed his/her end, sending a wave down the slinky toward the other person, we would notice that as the wave passes a particular coil, that coil moves in the same direction as that of the passing wave. We might also observe that the coils are closer together in the vicinity of the passing wave. These areas are called compressions, whereas the areas along the slinky in which the coils are stretched farther apart than normal are called rarefactions. In today’s lab, we will observe both kinds of waves. With the vibrating string, we will see up-and-down motion by the string as the wave passes from one side to the other. With the resonance column, we will be dealing with sound waves, which are longitudinal waves. One last general point of wave motion (and this applies to ALL waves): the velocity of a wave equals the product of its frequency and its wavelengths, or v = ± f. For example, since the speed of sound in air is roughly 340 m/s, then sound at a freq. of 1000 hz (cycles per sec) has a ± of 0.34 m, and sound at a freq. of 500 hz has a ± of 0.68 m.
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2 Discussion Part I: The velocity of wave traveling down a string depends on two factors: the tension in the string and the mass per unit length of the string (called linear mass density). The relation
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