Chapter 13 - Lecture notes 13.1 PDF

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Lecture notes for chapter 13 part 1 ...

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Chapter 13.1 Sunlight Questions associated with sunlight 1. Why is the sky blue? 2. 2. Why are sunsets red? 3. What causes a rainbow? The first two involve Rayleigh Scattering, the ability of tiny particles to absorb light, become tiny antennae, and radiate the light at different wavelengths. The radiated light occurs for all angles including directions perpendicular to the original light path. This happens more easily for blue light. As the light from the sun passes overhead the Rayleigh scattered light is directed downward and is mainly blue. At sunsets where the light from the sun travels great distances more or less parallel to the earth’s surface. The blue light is removed and the remaining Rayleigh scattered light is red. Sunlight that enters a water droplet is first bent (refracted) at the he first surface. Then it is reflected at the back surface. The reflection is due to the sudden change in index of refraction, n, called impedance matching. The light goes back to the front surface where it is refracted again, this time away from the normal. The angle of refraction is different for different wavelengths. Violet is bent more,

There is one other important property of light crucial for rainbows. This is dispersion, the speed of the light in the medium depends on the wavelength. Red light travels about 1 % faster through water than violet light. This also aids in separating the colors that emerge from the drop. Thin films Think of a layer of oil on a water surface. The reflected light is typically in circles of different colors. This has to do with interference of the light reflected from the upper and lower surfaces of the oil. The path difference between the ray reflected from the lower surface and the ray reflected from the upper surface determines whether the interference will be constructive or destructive. A path difference of 2  will produce constructive interference. Polarization by reflection Certain materials called polarizers have the ability to only allow electric field that are in the vertical x-y plane to pass through. The transmitted light is called linear or plane polarized light. Normal unpolarized slight can strike a surface at a shallow angle, like sunlight bouncing off a highway into your eye. The light polarized perpendicular to the surface dies. It has difficulty causing the atoms of the surface to oscillate. The light polarized parallel to the surface causes the atoms of the surface to vibrate parallel to the surface. The antennae radiate light polarized parallel to the surface.

Polarized glasses that only allow vertically polarized light through will absorb this horizontally polarized light, eliminating the glare....