Class 35. Wave properties. PHY 231 Fall 2004 Prof. S. Billinge

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Eugene Dixon
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1 Class 35 Wave properties

2 Announcements Clicker scores were sent by message to LONCAPA. Please check and report problems to me ASAP

3 Concepts overview 1. Wavelength, amplitude, frequency, period 2. Superposition of waves 1. Constructive/destructive interference 3. Reflection of traveling waves 4. Sound 1. Speed of sound 2. Energy and intensity of sound

4 v = fλ Wavelength, amplitude, velocity

5 The green arrow on the figure above indicates the wave s: 1. Wavelength 2. Half wavelength 3. Period 4. Amplitude 5. Half-amplitude

6 The green arrow on the figure above indicates the wave s: 1. Wavelength 2. Half wavelength 3. Period 4. Amplitude 5. Half-amplitude 6. None of the above

7 x The green arrow on the figure above indicates the wave s: 1. Wavelength 2. Half wavelength 3. Period 4. Amplitude 5. Half-amplitude 6. None of the above

8 A wave is sent along a long spring by moving the left end rapidly to the right and keeping it there.the figure shows the wave pulse at QR part RS of the long spring is as yet undisturbed.which of the graphs 1 5 correctly shows the relation between displacement s and position x? (Displacements to the right are positive.)

9 Waves on a string Wave velocity v = F µ F = tension in the string µ = mass per unit length Note about reflection of waves Fixed end, reflected pulse is inverted Free end, reflected wave is not inverted

10 A violin string is replaced with another of four times the mass/unit length and pulled to the same tension as before. What happens to the frequency of the sound. 1. It is 4x higher 2. It is 4x lower 3. It doubles 4. It is halved 5. None of the above

11 By shaking one end of a stretched string, a single pulse is generated.the traveling pulse Carries 1. energy. 2. momentum. 3. energy and momentum. 4. neither of the two.

12 Superposition and interference

13 Two identical pulses of opposite amplitude travel along a stretched string and interfere destructively. Which of the following is/are true? 1. There is an instant at which the string is completely straight. 2. When the two pulses interfere, the energy of the pulses is momentarily zero. 3. There is a point on the string that never moves up or down and and 3

14 A string is clamped at both ends and plucked so it vibrates in a standing mode between two extreme positions a and b. Let upward motion correspond to positive velocities.when the string is in position c, the instantaneous velocity of points along the string: 1. is zero everywhere. 2. is positive everywhere. 3. is negative everywhere. 4. depends on location.

15 A string is clamped at both ends and plucked so it vibrates in a standing mode between two extreme positions a and b. Let upward motion correspond to positive velocities.when the string is in position b, the instantaneous velocity of points along the string 1. is zero everywhere. 2. is positive everywhere. 3. is negative everywhere. 4. depends on location.

16 Sound Wave velocity (speed of sound) v = B ρ B = bulk modulus (compressibility) of the fluid (e.g., air) = - V P/ V ρ = density

Phys101 Lectures 28, 29. Wave Motion

Phys101 Lectures 28, 29. Wave Motion Phys101 Lectures 8, 9 Wave Motion Key points: Types of Waves: Transverse and Longitudinal Mathematical Representation of a Traveling Wave The Principle of Superposition Standing Waves; Resonance Ref: 11-7,8,9,10,11,16,1,13,16.