Presentation on theme: "What is polarized light? x Looking "head-on" we only see the blue arrows up & down y z x y z Light is polarized if the light wave and electric force field."— Presentation transcript:
What is polarized light? x Looking "head-on" we only see the blue arrows up & down y z x y z Light is polarized if the light wave and electric force field arrows remains in the same plane – The (blue) arrows must be perpendicular to the ray This is a light ray traveling in the z- direction and polarized in the y- direction Here is a light ray traveling in the same direction but polarized in the x- direction We see the polarization in the x-y plane, looking at rays head-on – The blue arrows point up and down or left and right, stacked up behind one- another.
y x What is unpolarized light? For unpolarized light the plane of polarization keeps jumping around – But the electric field arrows remain perpendicular to the ray (direction of travel of the wave) – We visualize this in the x-y plane (looking into the ray) as shown at right The many crossed double sided arrows are the symbol for unpolarized light See Physics 2000 x y z electric force arrows jump around while remaining perpen- dicular to the ray wave travels in z-direction
3 Polarization Polarization is a phenomenon of light that is used in sun-glasses, photography and 3-D movies. Play with the two polarizing filters for a few minutes and note what is happening and see if you can think of any reasons for it.
4 Polarization Hint Light vibrates in all directions. A polarizing filter acts like a picket fence. It only lets certain direction vibrations pass through it. Therefore, if you pass light through two of them you can completely block the light from passing through. HOW?
For light: Polarizers (Polaroid films) Same story:
Polaroid sunglasses (and camera filters) take advantage of this effect to block bright reflected light from the snow, beach, road, water, sky, etc. When you wear polaroid sunglasses they block light polarized in the plane of your two eyes – When your head is vertical this is the horizontal plane – Since reflected light from the ground or scattered light from the sun are mostly polarized in the horizontal plane such light is mostly blocked Demo with polaroid filters – The first filter blocks one polarization and lets through the other (perpendicular) one – The second blocks more and more of the remaining polarized light as its axis is rotated so as to permit only the polarization blocked by the first – When the axes of the two polaroid filters are at right angles to each other no light comes through
Polarization Photography Reduce Sun Glare Reduce Reflections Darkens Sky Increase Color Saturation Reduce Haze
Polarization Photography Without Polarizer With Polarizer Provides better Color Saturation Darkens the sky
Polarization Photography Without Polarizer With Polarizer
Light as Plane Waves Polarized Wave: Has only one preferred orientation. Un-polarized Wave: Has no preferred orientation. or has all orientations. Partially polarized wave: Has preferred orientation but has energy in other orientations as well. 180 o
Polarizer Puzzle If crossed polarizers block all light, why does putting a third polarizer at 45° between them result in some transmission of light?