http://www.ck12.org Chapter 21. Physical Optics
FIGURE 21.18
Vertical and horizontal transverse wavesOrdinary non-polarized light can be made polarized by two methods: polarization by transmission and polarization
by reflection.
Polarization by Transmission.
Certain transparent materials (called polarizers) have long chains of parallel molecules that act like the slots de-
scribed above. For instance, the mineral tourmaline is a known polarizer. However, most polarizers used in everyday
life are synthetic plastic.
A polarizer only allows through the vibrations that occur in a particular plane.Figure21.19 shows how a polarizer
permits a particular plane of the vibrating electric field to pass if it is aligned with the chains of molecules (top
figure) and how a polarizer that is oriented perpendicular to the vibrations (bottom figure) block the vibrating electric
field. Note that the direction of those molecular chains, defining the direction of polarization, is called the axis of
polarization.
FIGURE 21.19
To help clarify the idea, consider an example of polarized mechanical waves, such as a rope that is moved up and
down in a vertical plane. Under this condition, the rope can be considered a vertically polarized wave. A set of
vertical slots as shown inFigure21.20, can serve as a polarizer. If the rope is shaken in the vertical plane, the
vibrations will pass through the slots. If the rope is shaken horizontally, the vibrations will not pass through the
slots.
Conversely, if the slots are horizontal, then the vertical vibrations, as shown inFigure21.21, are prevented from