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Waves

Waves. Waves. Waves transmit energy and information . Sound and Light are both waves. There are two ways to transmit information/energy in our universe:. Particle Motion and Wave Motion. 1. VIBRATION OF A PENDULUM. Demo -Ball pendulum. What does the period (T) depend upon?

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Waves

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  1. Waves

  2. Waves • Waves transmit energy and information. • Sound and Light are both waves.

  3. There are two ways to transmit information/energy in our universe: Particle Motion and Wave Motion

  4. 1. VIBRATION OF A PENDULUM • Demo -Ball pendulum • What does the period (T) depend upon? • Length of the pendulum (l). • Acceleration due to gravity (g). • Period does not depend upon the bob mass.

  5. When oscillations are small, the motion is called simple harmonic motion (shm) and can be described by a simple sine curve.

  6. Sine Curve Wavelength  Amplitude A

  7. Crest l Wavelength A A - Amplitude Trough 2. WAVE DESCRIPTION Picture of a Transverse Wave

  8. - meters or feet Distance between adjacent crests in a transverse wave Distance a wave travels during one vibration Units Wavelength (l)

  9. Period (T) Time required to make one vibration. • Time required to generate one wave. • Time required for the wave to travel one wavelength.

  10. The number of vibrations per unit of time made by the vibrating source. Units - cycles per second 1/s Hertz (Hz) Frequency (f)

  11. Examples of Frequency • What is the frequency of the second hand of a clock? Frequency = 1cycle/60 sec Period = 60 sec • What is the frequency of US Presidential elections? Frequency = 1 election/4 yrs Period = 4 yrs

  12. Period Frequency

  13. 3. WAVE MOTION • Energy is transported by particles or waves. • A wave is a disturbance transmitted through a medium. • Exception: light does not require a medium.

  14. Demo - Waves on a rope A disturbance moves through the medium. Elements of the medium vibrate. Examples: ripples on water wheat waves

  15. 4. WAVE SPEED The average speed is defined as

  16. For a wave, if the distance traveled is a wavelength (l), then the time to travel this distance is the period (T). Thus or

  17. is true for all waves. Note: v is dictated by the medium. f is dictated by the source.

  18. Particles vibrate perpendicular to the motion of the waves Slinky Transverse Waves Examples: string musical instruments ripples on water electromagnetic waves e.g. Light waves. Seismic “S”-waves. 5. TRANSVERSE WAVES

  19. Picture of a Transverse Wave Crest l Wavelength A A - Amplitude Trough

  20. 6. LONGITUDINAL WAVES Particles vibrate Parallel to the motion of the waves - Slinky Longitudinal Waves e.g.Sound. Seismic P-waves.

  21. Parameters Rarefactions are regions of low density. Compressions (condensations) are regions of high density. l is the distance between…... ………….successive rarefactions or ………….successive compressions.

  22. Demo - Slinky

  23. 7. Super position INTERFERENCE Superposition of Waves Overhead - Interference

  24. Superposition A number of different waves can add, constructively or destructively. The superposition of two or more waves results in interference.

  25. Interference The superposition of two or more waves results in interference.

  26. Interference Pattern The pattern formed by superposition of different sets of waves that produce mutual reinforcement in some places and cancellation in others.

  27. Destructive Interference: Exactly out of Phase Cancellation + Zero displacement

  28. Destructive interference occurs when waves are out of phase, that is when crests are superimposed with troughs.

  29. Constructive Interference: Reinforcement +Maximum In phase displacement

  30. Constructive Interference occurs when waves are in phase, that is when crests are superimposed and troughs are superimposed.

  31. Constructive and Destructive Interference Two Slit Interference

  32. Interference is a characteristic of all waves.

  33. Standing Waves • When two sets of waves of equal amplitude and wavelength pass through each other in opposite directions, it is possible to create an interference pattern that looks like a wave that is “standing still.” • Demo - Rope and strobe • Demo - Mechanical overhead model

  34. Standing Wave Incident Wave V Reflected Wave V V Standing Wave V

  35. l Standing Waves

  36. There is maximum vibration at an antinode. l is twice the distance between successive nodes or successive antinodes. l There is no vibration at a node.

  37. There is maximum vibration at an antinode. l is twice the distance between successive nodes or successive antinodes. Notes on Standing Waves • There is no vibration at a node.

  38. Demo- Soda straw wave machine • Demo - tuning fork • Another example: musical instruments • Demo- Drumhead Vibrations

  39. 8. DOPPLER EFFECT • Refers to the change in frequency when there is relative motion between an observer of waves and the source of the waves • Doppler with Sound • Doppler with Water

  40. Doppler Effect The shift in received frequency due to motion of a vibrating source toward or away from a receiver.

  41. Doppler Effect Notes Motion of Source Sound Light and Observer Moving together Higher “Blue Shift” Pitch Moving Apart Lower “Red Shift” Pitch

  42. True Velocity Radial Velocity Tangential Velocity Radar Doppler Shift Gives Radial Velocity

  43. Lab Absorption Spectrum of Element X Star Absorption Spectrum of Element X Red Shifted Red Shift Star is moving away from us.

  44. Bow Wave The V-shaped wave made by an object moving across a liquid surface at a speed greater than the wave speed. (Since the source is moving faster than the wave speed, the wavefronts pile up.)

  45. 9. BOW WAVES • Waves in front of moving object pile up. • Demo - Barrier slide • Demo - “Bow” wave slide

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