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Summary

• What is a wave: a moving (or changing) pattern
• Water waves (height)
• Vibration of string: (displacement)
• Sound: pressure wave
• Light: Electromagnetic wave (also radio, x-rays, ...)
• Waves described by:
• Amplitude, frequency - f, wavelength - lambda
• Velocity v = lambda f
• Velocity of waves determined by the medium through which it is transmitted
• Sound in air, around 340 m/s
• Light in vacuum, around 3 x 10⁸ m/s
• Interference is a key general property of waves
• Examples of sound (interference of sound from 2 speakers), light (interference of light from 2 slits)
• Contrast with particles - objects with mass - do NOT show interference
• Particles and waves COMPLETELY different in classical physics
• Standing waves
• Examples of waves on a string
• Only waves with N (lambda/2) = L are allowed, where L = length, lambda = wavelength, and N = an integer
• Since v = lambda f, this also means only certain frequencies, N (v/2f) = L or f = N (v/2L)
• Next Time: Does the earth really move?
  How the wave mnature of light is used to test the question:
  Is the earth moving relative to some absolute reference.
• Read for Next Time: March, Chapts. 8