1. 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

2. 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 p 742 and 743.

3. 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)

4. 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 p747

5. 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 ( )
See Example p 749

6. 24-11 Scattering of Light by the Atmosphere

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