In Concept 3 you see an end-on “close up” of several light waves striking a polarizing
filter that has a vertical transmission axis. The light waves are coming toward you. In
each case, the vertical component of the electric field of the light is transmitted, and the
filter absorbs the horizontal component. The original field is shown as a solid, dimmed
vector; its components are hollowed out. The vertical component that passes through is
drawn with a bright color, and the horizontal component that is blocked is dimmed and
marked with a red ×. In each example illustrated, the electric field amplitude of the
transmitted light, and with it the light's intensity, is reduced.
The final illustration, in Concept 4, displays an experiment with two polarizing filters.
Unpolarized light is coming toward you from a distant source. It passes first through the
upper filter, which allows the passage of light that is polarized at the angle shown by the
“slit” lines. This polarized light continues toward you and passes through the lower filter.
The left-hand part of the illustration shows the orientation of the filters, with parallel lines
indicating the transmission axis of each filter. The right-hand side shows you the
amount of light that passes through the area of overlap, and how that changes with the
angles between the two axes. When the axes are perpendicular, no light at all can pass
through.
Radiation also can be partially polarized, having a few waves oscillating in all planes,
but with most of its waves concentrated in a single plane. This is true of sunlight
scattered by the atmosphere. As the photo above shows, the sky in certain directions is
partially polarized in a vertical plane so that most of its light can pass through a pair of
sunglasses whose transmission axis is vertical. Less light (but still some) passes
through the rotated sunglasses. (Polarizing sunglasses are specifically intended to
reduce horizontally polarized glare reflected from roadways and water, not skylight.)
Many forms of artificial electromagnetic radiation are polarized. A radio transmitter emits
polarized radiation. If the rods of its antenna are vertical, then so is the electric field of
every radio wave it creates. In this case, the most efficient receiving antenna is also
vertically oriented; a horizontal receiving antenna would absorb radio waves much less
efficiently. You may be familiar with this fact if you have ever tried to maneuver a radio
antenna wire or a set of television “rabbit ears” to get the best reception. (If you do not
know what “rabbit ears” are for television, well, before there was cable television, there
was....)
Polarized light
The filter transmits polarized light
·Incoming light is unpolarized
·Transmitted light vertically polarized
·Transmitted waves all in same planeE-field component passes
through filter
If transmission axis is vertical, filter ...
·Transmits vertical E-field component
·Absorbs horizontal E-field componentTwo Polaroid filters
Light passes through back (upper) filter
Then passes through front (lower) filter
Intensity depends on orientation of filters