Refraction

1. Refraction

2. 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. Changing Speed

3. Air 1.00029 Ice 1.31 Water 1.333 Alcohol 1.36 Quartz 1.4584 Plexiglas 1.51 Crown glass 1.52 Flint glass 1.66 Zircon 1.923 Diamond 2.417 Values at 589 nm Every transmitting medium has its own index of refraction. Clear Media

4. The geometry for refraction follow the same rules as reflection. Normal to the surface Incident angle qi Reflected angle qr There is also a refracted ray. Transmitted angle qt Refraction Geometry

5. 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. Snell’s Law

6. Light is refracted into a crown glass slab at 30.0°. Find the angle in crown glass. n1 = 1.00 and n2 = 1.52 θ2 = sin-1(n1 / n2) sin θ1 = 19.2o The ray bends toward the normal. Always true for the higher index of refraction Bending In

7. 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. Bent Rays

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

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

10. 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. Prism

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