LIGHT OBSERVATIONS 1 Light propagates in straight lines

LIGHT: OBSERVATIONS 1. Light propagates in straight lines from a source. Makes triangulation, surveying, star location, etc. possible.

REFLECTION normal qi qr air glass qi = qr Incident ray, reflected ray, normal, lie in a plane.

REFRACTION Li gh t. B Air ea m qi Water qr qi > qr

VARYING qi FOR AIR/WATER qi qr qi/qr sinqi/sinqr 10 30 60 80 7. 5 22. 1 40. 6 47. 8 1. 33 1. 36 1. 48 1. 68 1. 33

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

LIGHT PIPES

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

COLOR

INTERPRETATION The index of refraction varies with color. For Glass: Red: 1. 514 Green: 1. 520 Violet: 1. 529

POLARIZATION x z y I(q) = I 0 cos 2(q)

THE RAINBOW 420 maximum return angle

BACKSCATTERING CONE no bac kscatte ring From sun backs catteri ng

CORNER REFLECTOR q q

CRUDE LENS

CRUDE LENS

AIR BUBBLE IN WATER

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 vair qi air water qr vwater vpar

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

Decisive Test of Particle Theory fixed mirror water-filled tube source rotating mirror air water