24-8 Interference by Thin Films When a liquid, with lower n, makes a film on top of water (or other liquid), the reflection occurs both at the surface and at the second liquid for portions of the light. Each color has a different response to the refraction and interference makes one color bright at each viewing angle. (See p740 figure 24-29) Newton’s rings can be formed in a similar way with a planoconvex lens setting on a flat-reflective surface. See pg 740 figure 24-30

24-8 Interference by Thin Films If light is reflected by a material whose n is greater than that of the original material, the phase changes by 1/2l. …if the n values relationship is changed…n2 < n1 then no change occurs. See Example 24-8 p 741. Thin films can cut down on reflected light. See Example 24-9 and 24-10 p 742 and 743.

24-9 Michelson Interferometer Interference by thin films is the basis of the Michelson interferometer, invented by Albert Michelson. This device uses a half-mirrored surface and 2 other mirrors, one movable to measure very small distances. (See p 745 figure 24-39)

24-10 Polarization When light is polarized from multiple directions down to only one plane of travel, we say it has been plane-polarized. When light is non-polarized, it has light waves traveling in all 3-d planes. Polarizing materials were discovered by Edwin Land in 1929. The intensity of a plane polarized beam can be calculated by I=I0 cos2q See Example 24-11 p747

24-10 Polarization Reflected light can be polarized by reflection. The amount of polarization can be determinded if you know the angle and the n values for the 2 media. Tan qp = n2/ n1 …if n1 is air, then … Tan qp = n2 is called Brewster’s angle…after David Brewster (1781-1868) See Example 24-13 p 749

24-11 Scattering of Light by the Atmosphere

HOMEWORK P754 ADD 38-40, 49,54-56