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Sound and Light

Sound and Light . ISCI 2002. Introduction . Sound and Light Travel in waves Waves - vibrations Sound Propagation of vibrations through a medium (solid, liquid, gas) Electromagnetic Spectrum Light Sound . Properties of Waves. Amplitude Wavelength Frequency (Hz) Period .

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Sound and Light

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  1. Sound and Light ISCI 2002

  2. Introduction Sound and Light Travel in waves Waves - vibrations Sound • Propagation of vibrations through a medium (solid, liquid, gas) • ElectromagneticSpectrum • Light • Sound

  3. Properties of Waves • Amplitude • Wavelength • Frequency (Hz) • Period

  4. Wave Speeds WaveSpeed = 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)

  5. Types of Waves TransverseWaves • Side-ways or right angle motion to the direction of the wave (radio waves, light waves) LongitudinalWaves • Travels along the direction of the source of the vibration • “waves of compression”

  6. Origins of Sound How is soundcreated? Compressions and Rarefacations • Compressions (WL bunched together) • Rarefacations (WL spread out)

  7. 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)

  8. Speed of Sound Speed of Sound • Depends on the medium • Faster • Water vapor; warm air RoomTemperature (20 degrees Celsius) • 340 m/s

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

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

  11. 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 TransparentObjects OpaqueObjects

  12. Refraction Wave speed changes with the mediumencountered. “Bendslight” How refraction occurs Index of Refraction (n) • c/v

  13. Dispersion and Lens • Eye Lens is biconvex • Focuses light onto the Focal Point at the back of the eye – Retina

  14. Color Colorsobserved – wavelengths of light Lowfrequencies – Red Higherfrequencies – 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”

  15. Color Mixing Allcolors 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

  16. Color Mixing PrimaryColorAddition • Red + Blue = Magenta • Red + Green = Yellow • Blue + Green = Cyan ComplementaryColors • Add together to produce white • Magenta + Green (Red + Blue + Green) • Cyan + Red (Blue + Green + Red) • Yellow + Blue (Red + Green + Blue)

  17. 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.

  18. Applications Applies to LightWaves • Blue shift vs Red shift • Galaxies and the expanding universe • Edwin Hubble The universe is expanding?

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