LIGHT: OBSERVATIONS

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# LIGHT: OBSERVATIONS - PowerPoint PPT Presentation

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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Presentation Transcript
LIGHT: OBSERVATIONS
• Light propagates in straight lines
• from a source.

Makes triangulation, surveying,

star location, etc. possible.

REFLECTION

normal

qr

qi

air

qi = qr

glass

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

REFRACTION

Light Beam

qi

Air

Water

qr

qi > qr

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

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

glass or plastic

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

The index of refraction varies with color.

For Glass:

Red: 1.514

Green: 1.520

Violet: 1.529

x

z

y

POLARIZATION

I(q) = I0cos2(q)

THE RAINBOW

420 maximum

return angle

BACKSCATTERING CONE

no backscattering

From

sun

backscattering

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

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?

vpar

vpar

qi

vair

air

water

qr

vwater

NEWTON’S EXPLANATION OF SNELL’S LAW

sin(qi) = vpar/vair

sin(qr) = vpar/vwater

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

OTHER PROPERTIES

Colors

Polarization

water-filled tube

Decisive Test of Particle Theory

fixed mirror

source

rotating

mirror

air

water