Refraction

Changing Speed  The speed of light in a material depends on the electromagnetic properties. Permittivity and permeability  The ratio of the speed in a material to that of a vacuum is the index of refraction.

Clear Media  Air  Ice1.31  Water1.333  Alcohol1.36  Quartz  Plexiglas1.51  Crown glass1.52  Flint glass1.66  Zircon1.923  Diamond2.417 Values at 589 nm  Every transmitting medium has its own index of refraction.

Refraction Geometry  The geometry for refraction follow the same rules as reflection. Normal to the surfaceNormal to the surface Incident angle  iIncident angle  i Reflected angle  rReflected angle  r  There is also a refracted ray. Transmitted angle  tTransmitted angle  t

Snell’s Law  The ratio of the sines of the incident and reflected angles is proportional to the relative wavelengths in the material.  The wavelength is inversely proportional to the index.  Combined they become Snell’s law of refraction.

Bending In  Light is refracted into a crown glass slab at 30.0°. Find the angle in crown glass. n 1 = 1.00 and n 2 = 1.52n 1 = 1.00 and n 2 = 1.52 θ 2 = sin -1 (n 1 / n 2 ) sin θ 1 = 19.2 oθ 2 = sin -1 (n 1 / n 2 ) sin θ 1 = 19.2 o  The ray bends toward the normal. Always true for the higher index of refractionAlways true for the higher index of refraction

Bent Rays  The refraction at the interface between water and air can cause objects to appear in the wrong place.  A split spoon in a clear glass of water is a common example.

Mirage  Air temperature affects the index of refraction. Lower for less dense, hot airLower for less dense, hot air  The difference causes refraction.

Inversion  At some times of the year there is a layer of cool air near the ground. Inverted mirageInverted mirage

Prism  The index of refraction depends on the wavelength. Longer wavelengths - lower indexes  A triangular prism has two refracting surfaces. One into glass One back to air  The wavelengths are separated into a spectrum.

Polarization  At an interface light becomes partially polarized. Separated beams reflected and transmittedSeparated beams reflected and transmitted  If the beams are perpendicular then the reflected ray is fully polarized. Brewster’s angleBrewster’s angle next