SOUND and LIGHT

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SOUND and LIGHT
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SOUND WAVES

• Remember, they are mechanicalmust have a medium.
• They are longitudinal so air molecules move
  parallel to the direction of the wave.

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Direction of Wave

• Energy travels out in all directions from
  vibrating object.

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Intensity of Sound

• The amount of energy in a wave.
• Intensity determines the amplitude of a wave.
• Intensity relates to the loudness of a sound -
  the greater the intensity, the louder the sound.

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Intensity

• Decibels (dB) - the units of intensity.
• Sounds over 120 dB will cause pain in the ears.
• Ear damage can begin with exposure to sounds as
  low as 85 dB.

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Decibels of other Sounds

• 40quiet conversation
• 60busy street
• 75vacuum cleaner
• 85heavy truck traffic
• 110power tools
• 140singer screaming into microphone
• 155jet engineup close

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Pitch

• This is how high or low a sound seems.
• A bird makes a high pitch. A lion makes a low
  pitch.
• Pitch has to do with frequency and amplitude.

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More on Pitch

• The amount of frequency depends on the amplitude
  of the wave.
• High pitch high frequency, shorter amplitude
• Low pitch low frequency, larger amplitude

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Hearing Frequencies

• Humans hear between 20 Hz and 20,000 Hz.
• Ultrasonicfrequencies above 20,000 Hz dogs and
  bats can hear ultrasonic
• Infrasonicfrequencies below 20 Hz wind,
  earthquakes, heavy machinery

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DOPPLER EFFECT

• An apparent frequency shift due to the relative
  motion of an observer and a wave source.
• The pitch will seem to change due to the wave
  moving.

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• As wave approaches you, you perceive a higher
  pitch.
• As wave moves away from you, you perceive a lower
  pitch.
• http//www.cpo.com/Weblabs/chap2/doppler4.htm

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What is happening here?
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What Can Sound Do?

• Can reflectsome sounds produce echoes when it
  bounces off hard surfaces.

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• Can interfere
• Destructivemakes sounds quieter
• Constructivemakes sounds louder

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LIGHT

• Can reflectobeys the Law of Reflection angle
  of incidence is equal to the angle of reflection.
  
• Can reflect in mirrorsupright, same size image
• Can diffract

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• Can interfere both constructively and
  destructively sometimes produces a color
  pattern. (Think about bubbles)

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REFRACTION OF LIGHTPRISMS

• Light slows down when it enters a prism and bends
  down when it strikes at this angle.
• When light exits the prism, it speeds back up and
  bends down again.

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• When white light enters another medium, the
  colors may spread out. Violet end slows down
  more than the red end, so it bends more.

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INDEX OF REFRACTION--Examples
Substance   Index of Refraction      n Substance Index ofRefraction      n
Diamond 2.419 Ethyl Alcohol 1.361
Cubic Zirconia   2.21 Ice 1.309
Glass (flint) 1.66 Water   1.333
Glass (crown) 1.52 Air 1.000
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LENSES

• Lenses can be convex (converging)
• Used on people with farsightedness (cant see up
  close)

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• Or lenses can be concave (diverging)
• Used on people with nearsightedness (cant see
  far away)