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?