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Waves

Waves. Mrs. Kay Physics 11. Wave. A disturbance that causes a transfer of energy over a distance, without a net transfer of mass. A single disturbance is called a pulse. Periodic Wave. A continuous series of disturbances High point = crest Low point = trough. Transverse Waves

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Waves

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  1. Waves Mrs. Kay Physics 11

  2. Wave • A disturbance that causes a transfer of energy over a distance, without a net transfer of mass. • A single disturbance is called a pulse

  3. Periodic Wave • A continuous series of disturbances • High point = crest • Low point = trough

  4. Transverse Waves • For transverse waves the displacement of the medium is perpendicular to the direction of propagation of the wave. • A ripple on a pond and a wave on a string are easily visualized transverse waves.

  5. Longitudinal Waves • In longitudinal waves the displacement of the medium is parallel to the propagation of the wave. A wave in a "slinky" is a good visualization. Sound waves in air are longitudinal waves.

  6. Wave Properties • Period: the time required to complete a full cycle, T in seconds/cycle • Frequency: the number of cycles per second, f in 1/seconds or Hertz (Hz) • Amplitude: the maximum displacement from equilibrium • Wavelength: repeat distance of wave λ

  7. The motion relationship "distance = velocity x time" is the key to the basic wave relationship. • With the wavelength as distance, this relationship becomes λ=vT. • Then using f=1/T gives the standard wave relationship v=fλ

  8. Practice: • What is the period of a wave with a frequency of 5Hz? • What is the period of a wave if its velocity was 12m/s and its wavelength was 590nm? • Pg 293 #1-4 • Problems Pg304 #1-3

  9. Wave Interference • During the time when one wave passes through another we say that the waves interfere

  10. Constructive Interference • When the crest of one wave passes through, or is superpositioned upon, the crest of another wave, we say that the waves constructively interfere. • Link

  11. Constructive interference also occurs when the trough of one wave is superpositioned upon the trough of another wave.

  12. During any wave interference the shape of the medium is determined by the sum of the separate amplitudes of each wave. We often say that when waves interfere, amplitudes add.

  13. Destructive Interference • When the crest of one wave passes through, or is superpositioned upon, the trough of another wave, we say that the waves destructively interfere.

  14. During destructive interference, since the positive amplitudes from one crest are added to the negative amplitudes from the other trough, this addition can look like a subtraction. Link

  15. Wave Boundaries • Speed of a wave doesn’t depend on the frequency or amplitude of a wave • Speed depends on the properties of the medium the wave moves through. Ex: a water wave depends on depth A sound wave depends on air temperature

  16. Refraction It involves a change in the direction of waves as they pass from one medium to another. Refraction, or bending of the path of the waves, is accompanied by a change in speed and wavelength of the waves.

  17. Waves traveling from the deep end to the shallow end can be seen to refract (i.e., bend), decrease wavelength (the wave fronts get closer together), and slow down (they take a longer time to travel the same distance).

  18. Reflection of waves • Reflection of waves are represented using ray diagrams • A ray line is drawn at right angles to the incident ray ( or crest of the wave)

  19. The barrier is drawn at right angles to the normal • The angle between the ray of incident and normal is called angle of incidence • The angle between the ray of reflection and normal is called the angle of reflection • The law of reflection states that the angle of incidence is equal to the angle of reflection

  20. Reflection off a curved surface: the water waves will change direction and head towards a point. All the energy carried by the waves is converged at a single point known as the focal point.

  21. Diffraction diffraction involves a change in direction of waves as they pass through an opening or around a barrier in their path.

  22. The waves are seen to pass around the barrier into the regions behind it; subsequently the water behind the barrier is disturbed. The amount of diffraction (the sharpness of the bending) increases with increasing wavelength and decreases with decreasing wavelength.

  23. Problems • Pg 297 # 5-8 • Pg 304 #4,5,7,8

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