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# Lecture25 - PHYSICS 149 Lecture 25 Chapter 12 Sound 12.4...

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PHYSICS 149: Lecture 25 • Chapter 12: Sound – 12.4 Standing Sound Waves • Chapter 13: Temperature and the Ideal Gas – 13.1 Temperature – 13.2 Temperature Scales Lecture 25 Purdue University, Physics 149 1

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Final Exam • Thursday, May 5, 3:20 – 5:20 PM • Place: PHYS 333 • Chapters 1 – 15 (only the sections we covered) • The exam is closed book. • The exam is a multiple-choice test. • There will be 30 multiple-choice problems. – Each problem is worth 10 points. • You may make a single crib sheet. – you may write on both sides of an 8.5” × 11.0” sheet. • Review session: Monday April 25, 10:30 AM • Conflicts: I need to know by Monday Apr 25. • Adaptive learners should contact Prof. Neumeister ASAP Lecture 10 2 Purdue University, Physics 149
Lecture 25 Purdue University, Physics 149 3 Two strings, one thick and the other thin, are connected to form one long string. A wave travels along the string and passes the point where the two strings are connected. Which of the following does not change after crossing that point: A) frequency B) wavelength C) propagation speed ILQ 1

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ILQ 2 Standing waves are produced by the superposition of two waves with a) the same amplitude and direction of propagation, but different frequencies. b) the same amplitude, frequency, and direction of propagation. c) the same amplitude and frequency, and opposite propagation directions. d) the same amplitude, different frequencies, and opposite directions of propagation. Lecture 25 4 Purdue University, Physics 149
Standing Waves Standing waves occur when a wave is reflected at a boundary in such a way that the wave appears to stand still. In a standing wave on a string, every point moves (as a whole) in simple harmonic motion (SHM) with the same frequency. Every point reaches its maximum amplitude simultaneously, and every point also reaches its minimum amplitude (namely, zero) simultaneously as well. Nodes are points of zero amplitude (that is, points that never move); antinodes are points of maximum amplitude. The distance between two adjacent nodes is ½ λ . Fixed end of a string is always a node, because it never moves. Lecture 25 5 Purdue University, Physics 149

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Lecture 25 Purdue University, Physics 149 6 • The natural frequency is related to the length of the string L. The lowest frequency (first harmonic) has one antinode • The second harmonic has two antinodes • The n-th harmonic Standing Waves
Sound Waves Sound is a longitudinal wave, with compressions and rarefactions of air.

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Lecture25 - PHYSICS 149 Lecture 25 Chapter 12 Sound 12.4...

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