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Waves

Waves. A wave is a vibratory disturbance that propagates through a medium (body of matter) or field. Examples of waves: sound, light, water waves, microwaves. Waves and Energy Transfer. Waves transfer energy from one place to another by repeated small vibrations of particles.

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Waves

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  1. Waves

  2. A wave is a vibratory disturbance that propagates through a medium (body of matter) or field. Examples of waves: sound, light, water waves, microwaves.

  3. Waves and Energy Transfer • Waves transfer energy from one place to another by repeated small vibrations of particles. • Waves ONLY transfer energy NOT mass. Notice that all the matter is in the same place after the wave has passed.

  4. Wave Types • Mechanical Waves: need a medium to travel through (air or water). • Sounds waves • Water waves

  5. Wave Types • 2. Electromagnetic Waves: do not need a medium to travel through and can travel through a vacuum. • Radio waves • Light waves

  6. Types of Wave Motion • Longitudinal Wave: a wave in which the motion of the vibration is parallel to the direction of wave travel. Ex. Sound waves, compression waves in a spring, and earthquake P-waves.

  7. Direction of wave motion Source Of Sound Wave This is how energy is transferred for a sound wave. Notice the individual particles remain in the same location after the wave passes by. Also notice that the direction of motion of the wave and the direction of particle motion is parallel to each other.

  8. This is how energy is transferred by compressing a spring or slinky.

  9. This is how energy is transferred through the earth with an earthquake P-wave. Notice the black square, it starts and ends in the same location showing us how waves transfer energy NOT matter.

  10. Types of Wave Motion • Transverse Wave: a wave in which the motion of the vibration is perpendicular to the direction of wave travel. Particle Motion Wave Motion Ex. Electromagnetic waves (light), earthquake S-waves.

  11. Particle Motion Wave Motion This is how energy is transferred in a transverse wave. Fix your eye on one of the particles. Notice it’s movement as the wave passes by. It moves up, then down, then back up again. This movement is perpendicular to the wave motion.

  12. This is how energy is transferred through the earth with an earthquake S-wave. Notice the black square, it moves up, then down, then back up to it’s original position showing us that only energy is transferred NOT matter.

  13. Unlike longitudinal waves, transverse waves can be oriented in many different planes.

  14. Pulses vs. Periodic Waves • A pulse is a single short disturbance or wave that moves from one place to another. The speed of the pulse depends on the medium.

  15. If a rope with a traveling pulse is attached to a fixed unyielding object, like a wall in the picture below, the pulse will be reflected. Reflection is the rebounding of a pulse or wave as it strikes a barrier.

  16. What specifically happens to the pulse when it hits the wall? Remember Newton’s 3rd Law? When the pulse arrives at the wall it exerts an upward force on the wall. The wall then exerts a force that is equal in magnitude (size of the wave doesn’t change) but opposite in direction. This reaction inverts the pulse.

  17. As a pulse reaches a new medium, part of the pulse is transmitted through the medium, part is absorbed, and part is reflected back towards the source. Low Density Medium to High Density Medium Reflected wave is inverted, transmitted wave is slower.

  18. High Density Medium to Low Density Medium Reflected wave is upright, transmitted wave is faster.

  19. A periodic wave is a series of pulses or evenly timed disturbances.

  20. Characteristics of Periodic Waves • The complete series of changes (one complete vibration) at one point in a medium as a wave passes is called a cycle. Here particles move forward and then back as the wave passes. This forward-back motion is one cycle.

  21. Here particles move up, down, then back to it’s original position as the wave passes. This up-down-up motion is one cycle.

  22. Frequency (f): # of cycles per second A frequency of 1 cycle per second is called 1 hertz (Hz). 1 Hz = 1 s

  23. Sound Waves and Frequency • The frequency of a sound wave determines the pitch. http://www.youtube.com/watch?v=d-XbjFn3aqE&feature=player_embedded

  24. Light Waves and Frequency • The frequency of a light wave determines its color.

  25. Try this… 10 wave cycles pass a fixed point in a medium in 5 seconds. What is the frequency (cycles per second) of the wave? f = 10 cycles 5 seconds = 2 cycles 1 second = 2 Hz

  26. Frequency of the Human Ear • Humans can detect frequencies in the range of 20 to 20,000 Hz. • How does the human ear work? http://www.youtube.com/watch?v=sxstfmtLVi0&feature=related http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter19/animation__effect_of_sound_waves_on_cochlear_structures__quiz_2_.html

  27. The frequency tells us how many cycles per second travel through a medium. Sometimes we just want to know the time it takes to complete only 1 cycle. This is the period (T) of a wave. T = 1 f

  28. Try this… The frequency of a wave is 2 hertz. What is the period of the wave? T = 1 f = 1 2 Hz = .5s It takes .5 s for one complete wave cycle to pass by a point in a medium.

  29. Try this… The frequency of a light wave is 5.0 x 1014 hertz. What is the period of the wave? T = 1 f = 1 5.0 x 1014 Hz = 2.0 x 10-15 s

  30. Which wave has the longest period (would take the longest time for one cycle to pass)?

  31. Amplitude: height of a wave

  32. The amplitude of a wave shows the amount of energy in a wave. • With sound waves amplitude is represented by loudness. Sound waves with large amplitudes are loud. • With light waves amplitude is represented by brightness. Light waves with large amplitudes are brighter.

  33. More wave characteristics: wavelength /condensations

  34. Wavelength (λ) • A wavelength is the distance between any two successive points in the same position on a wave. It’s the length of one complete wave cycle. λ λ Longitudinal Transverse

  35. What is the λ of the wave train below? 5 m 2.5 waves = 2 m

  36. Find the amplitude and λ for the series of waves below. λ= 1.5 m 2.5 waves = .6 m Amplitude = .1 m

  37. Wave Phase • Certain parts of a single wave have a phase associated with it. • Let’s start by looking at a circle: 90° 0° 180° 360° 270°

  38. Points on successive waves that are in the same position on the wave (360° apart or 1 wavelength apart) are said to be “in phase.” 360°/λ

  39. Which two points are in phase with each other? C and F

  40. Which 2 points are 180° out of phase? 1λ 2 B and D, or E and G

  41. Immediately after the wave moves through point A , will point B move up, down, left, or right? B A Before you answer any question like this make sure you re-draw the wave after it has moved. B A B would move up

  42. Speed of Waves v = fλ From this equation what is the relationship between frequency and wavelength? λ = v f Inverse relationship- if a wave has a high frequency then it is going to have a small or short wavelength.

  43. Find the velocity of the wave below if it has a frequency of 40 Hz. v = fλ v = 40 Hz(1.5 m) v = 60 m/s

  44. The speed of a wave depends upon its type and the medium through which it travels.

  45. Sound vs. Light Waves Remember sound and light waves are different types of waves. Sound – longitudinal. Light – transverse. Therefore they travel differently and at different speeds. Speed of Sound – 331 m/s (3.31 x 102 m/s) Speed of Light – 300,000,000 m/s (3.00 x 108 m/s) Light is 1 million times faster than sound!

  46. This is why you “see” lightning before you “hear” it. You can approximate the storms distance in miles by counting the seconds between the lightning and thunder. Every 5 seconds is approximately 1 mile.

  47. http://www.youtube.com/watch?v=-d9A2oq1N38&feature=player_embeddedhttp://www.youtube.com/watch?v=-d9A2oq1N38&feature=player_embedded When a source, this time something like a fighter jet, travels at a speed greater than the speed of sound, it actually outruns the sound waves, and is said to break the sound barrier, and arrives before the sound does.

  48. Try this… The following diagram shows a segment of a periodic wave in a rope traveling to the right to point G. • What type of wave is represented in the diagram? • What is the amplitude of the wave? • What is the wavelength of the wave? • If the frequency of the wave is 2 Hz, what is the period of the wave? • Determine the speed of the wave. • Name the two points on the wave that are in phase. • Immediately after the wave moves through point g, will point B move up, down, left, or right? 2.4 m 6.0 m

  49. Wave Fronts • In a 3-dimensional medium such as air, waves radiate in concentric spheres from a vibration point. Wavefronts/Crests Troughs

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