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?