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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 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
q CORNER REFLECTOR q
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