Sound and Light

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Sound and Light

• ISCI 2002

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Introduction

• Sound and Light Travel in waves
• Waves - vibrations
• Sound
• Propagation of vibrations through a medium
  (solid, liquid, gas)
• Electromagnetic Spectrum
• Light
• Sound

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Properties of Waves

• Amplitude
• Wavelength
• Frequency (Hz)
• Period

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Wave Speeds

• Wave Speed wavelength x frequency
• Example - Water waves
• Count time as crests pass by (period)
• Observe the distance between the crests
• Speed distance / time
• Distance (wavelength) / time (period)

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Types of Waves

• Transverse Waves
• Side-ways or right angle motion to the direction
  of the wave (radio waves, light waves)
• Longitudinal Waves
• Travels along the direction of the source of the
  vibration
• waves of compression

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Origins of Sound

• How is sound created?
• Compressions and Rarefacations
• Compressions (WL bunched together)
• Rarefacations (WL spread out)

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Nature of Sound

• Sound travels through all types of mediums
• Cannot travel through a vacuum
• Must have a medium to produce a vibration!
• Pitch
• How we perceive sound
• Human hearing (20 to 20,000 Hz)

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Speed of Sound

• Speed of Sound
• Depends on the medium
• Faster
• Water vapor warm air
• Room Temperature (20 degrees Celsius)
• 340 m/s

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Nature of Light

• Where does light come from?
• Acceleration of electrons
• Wave/particle (photons)
• Visible Light
• 400 nm to 700 nm
• Different frequencies (colors)
• Dependent on wavelengths
• Red vs Violet and Blue

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Speed of Light

• Speed of Light in a Vacuum
• 300,000 km/s or 186,000 m/s
• Atmosphere (75) Glass (67) Diamond (41)

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Reflection

• Reflection
• Law of Reflection The angle of reflection equals
  the angle of incidence
• Not all light is reflected
• Glass (4) Aluminum (90)
• Absorption and transmission
• Transparent Objects
• Opaque Objects

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Refraction

• Wave speed changes with the medium encountered.
• Bends light
• How refraction occurs
• Index of Refraction (n)
• c/v

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Dispersion and Lens

1. Eye Lens is biconvex
2. Focuses light onto the Focal Point at the back of
   the eye Retina

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Color

• Colors observed wavelengths of light
• Low frequencies Red
• Higher frequencies blue
• Color of an object
• What color it reflects (absorbs the others)
• Some objects color (yellow) reflect several
  frequencies of light (red, green and yellow)
• Selective Reflection vs Selective Transmission

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Color Mixing

• All colors combined white light
• Cones (photoreceptors in eyes)
• 3 types
• Low frequency (red) middle (green) high (blue)
  if all cones are stimulated at the same time ---?
  see white

Additive Primary Colors
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Color Mixing

• Primary Color Addition
• Red Blue Magenta
• Red Green Yellow
• Blue Green Cyan
• Complementary Colors
• Add together to produce white
• Magenta Green (Red Blue Green)
• Cyan Red (Blue Green Red)
• Yellow Blue (Red Green Blue)

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The Doppler Effect
The change of frequency of a wave as measured by
an observer due to the motion of the source or
due to the motion of the observer.
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Applications

• Applies to Light Waves
• Blue shift vs Red shift
• Galaxies and the expanding universe
• Edwin Hubble
• The universe is expanding?