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Sound and Light
ISCI 2002
Sound and Light Travel in waves
Waves - vibrations
Sound – Propagation of vibrations
through a medium (solid, liquid, gas)
• Electromagnetic Spectrum– Light – Sound
1. Amplitude
2. Wavelength
3. Frequency (Hz)
4. Period
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)
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”
How is sound created?
Compressions and Rarefacations– Compressions (WL
bunched together)– Rarefacations (WL
spread out)
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)
Speed of Sound – Depends on the medium – Faster • Water vapor; warm air
Room Temperature (20 degrees Celsius)– 340 m/s
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
Speed of Light in a Vacuum–300,000 km/s or 186,000 m/s –Atmosphere (75%); Glass (67%);
Diamond (41%)
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
Wave speed changes with the medium encountered.
“Bends light”
How refraction occurs
Index of Refraction (n)• c/v
1. Eye Lens is biconvex
2. Focuses light onto the Focal Point at the back of the eye – Retina
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”
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
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)
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.
Applies to Light Waves – Blue shift vs Red shift – Galaxies and the expanding universe – Edwin Hubble
The universe is expanding?
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