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Waves and Sound

Learn how to analyze pressure vs. time graphs to determine wave properties such as period and amplitude. Understand the concept of wavelength, medium, and wave velocity. Discover how to calculate wave speed in different mediums. Explore real-life applications of wave properties, such as using sound for distance measurement in auto-focusing cameras.

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Waves and Sound

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  1. Waves and Sound

  2. POD Use the pressure vs. time graph below to answer questions #1-2. 1. The period of the wave in the diagram above is given by letter ______. 2. The amplitude of the wave in the diagram above is given by letter _____. 3. Indicate the interval which represents one period. a. A to C b. B to D c. A to G d. C to G Answers 1. A 2. D 3.D

  3. Wavelength • The length of the wave for one cycle • From peak to peak • Trough to trough • MUST be in meters!!! • Cannot find wavelength on a time graph! • Symbol for wavelength is λ X λ pressure Distance (m)

  4. Medium • The material that carries the wave • The medium for sound in this room is air • The medium for a water wave is the ocean • The medium for a stadium wave is the people

  5. Motion is two dimensions • If you drop a pebble in a puddle • The wave moves from the splash to the edges of the puddle • The wave also moves up and down • The water from the splash does not move forward with the wave • Think of stadium wave you move up and down not to a new seat

  6. When an object oscillates • Energy is transferred from one place to another • The moving tuning fork moves the air • The compression of the air changes the pressure and the wave moves forward across the room • As the energy moves away from the source the intensity decreases

  7. The motion is in 2D so • There is velocity in both directions • As the wave moves forward it has a constant value that depends on the material • This velocity is called wave speed • This is the speed of the wave moving away from the source. • There is no net displacement • Stadium wave – the people stay in their seats but the wave goes around the stadium

  8. Wave speed V = fλ Wave velocity = frequency x wavelength V for sound is about 343m/s V=d/t

  9. The velocity of a wave • Is a constant value for a given medium • Is a property of the material • To change the velocity you must change the medium • Change the mass • The forces • The temperature • The density

  10. Go do tuning fork lab 2

  11. How to determine v in a medium • For the air TF = 9/5 TC + 32o TC = T - 273

  12. Auto focusing cameras use sound to determine the distance to the object to be photographed. Assuming the speed of sound is 340m/s, how much time is necessary to focus the camera if the person is 1m away? 20m away? Time = d/v must double distance 2/340 = 0.0059s and 0.12s

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