http://www.ck12.org Chapter 21. Physical Optics
Polarization by reflection
Light that reflects off of nonmetallic surfaces, such as water, glass, or pavement, is also polarized. The axis of
polarization is in the same plane as the surface off which the light reflects. For example, the light that reflects off
of a horizontal pavement is polarized parallel to the plane of the pavement. Light reflected off of the surface of the
ocean is polarized horizontally as well and accounts for most of the annoying glare we experience on sunny days.
Polarized sunglasses have a vertical axis of polarization in order to block the horizontally polarized light and reduce
that glare.
Camera lenses can be fitted with polarizers to minimize the effects of glare, as shown inFigure21.22. Notice how
the picture on the left shows the glare off of the water, but the picture on the right, taken with a polarizer, does not.
FIGURE 21.22
Light polarized by reflection is also a clue to astronomers who are searching for planets about other stars (extrasolar
planets). The light from extrasolar planets is often obscured by the much brighter light of the star it orbits. However,
the reflected light from the planet is polarized while the star light is not. Thus, astronomers have a “polarized light
signal” with which to search for extrasolar planets.
- When white light passes through a glass prism, a rainbow-like array of colors, called the visible spectrum, exits
the prism. The spreading of light in this manner is called dispersion. - Dispersion is caused by the fact that the speed of light in a medium other than vacuum depends on its frequency
(color). - Red light is refracted the least and violet light refracted the most.
- Light with wavelengthλin air, has a wavelengthλn=λnin a medium of refractive indexn.
5a. Constructive interference condition for a double-slit is arrangement given by the equation
dsinθ=mλ,m= 0 , 1 , 2 ,...
wheredis the distance between the slits,θis the diffracting angle,mis the order andλis the wavelength of the light.
5b. Destructive interference condition for a double-slit arrangement is given by the equation
dsinθ=
(
m+^12)
λ,m= 0 , 1 , 2 ,...6a. Constructive interference for a thin film of thicknessdand wavelength of lightλ(in the film) when there is no
effective phase change, is given by the equation