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LIGHT: OBSERVATIONS. Light propagates in straight lines from a source. Makes triangulation, surveying, star location, etc. possible. REFLECTION. normal. q r. q i. air. q i = q r. glass. Incident ray, reflected ray, normal, lie in a plane. REFRACTION. Light Beam. q i. Air.

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light observations
LIGHT: OBSERVATIONS
  • Light propagates in straight lines
  • from a source.

Makes triangulation, surveying,

star location, etc. possible.

reflection
REFLECTION

normal

qr

qi

air

qi = qr

glass

Incident ray, reflected ray, normal, lie in a plane.

refraction
REFRACTION

Light Beam

qi

Air

Water

qr

qi > qr

varying q i for air water

sinqi/sinqr

qi/qr

1.33

1.33

1.33

1.33

1.33

1.36

1.48

1.68

VARYING qi FOR AIR/WATER

qr

qi

7.5

22.1

40.6

47.8

10

30

60

80

index of refraction
INDEX OF REFRACTION

For light propagating between air and

another transparent material,

n = sinqi/sinqr

is the index of refraction of the material

The value of n depends on the material:

water: n = 1.33

glass: n = 1.5

diamond: n = 2.4

total reflection
TOTAL REFLECTION

glass or plastic

intersecting beams
INTERSECTING BEAMS
  • When two light beams intersect, they do not interact with each other at all.
interpretation
INTERPRETATION

The index of refraction varies with color.

For Glass:

Red: 1.514

Green: 1.520

Violet: 1.529

polarization

x

z

y

POLARIZATION

I(q) = I0cos2(q)

the rainbow
THE RAINBOW

420 maximum

return angle

backscattering cone
BACKSCATTERING CONE

no backscattering

From

sun

backscattering

newton s particle theory of light
NEWTON’S PARTICLE THEORY OF LIGHT

Light is made up of little particles.

They obey the same laws of physics as other masses

like baseballs and planets.

They are tiny so the particles in two intersecting

beams do not scatter off each other.

particle theory of refraction
PARTICLE THEORY OF REFRACTION

A light particle deep within a medium

experiences no net force.

Near an interface, e.g. between air and

water, light particles experience an

attractive force towards the water.

Could this be the cause of refraction?

slide20

vpar

vpar

qi

vair

air

water

qr

vwater

newton s explanation of snell s law
NEWTON’S EXPLANATION OF SNELL’S LAW

sin(qi) = vpar/vair

sin(qr) = vpar/vwater

sin(qi)/sin(qr) = vwater/vair

other properties
OTHER PROPERTIES

Colors

Polarization

decisive test of particle theory

water-filled tube

Decisive Test of Particle Theory

fixed mirror

source

rotating

mirror

air

water