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## Physics library

### Course: Physics library>Unit 14

Lesson 1: Introduction to electromagnetic waves

# Polarization of light, linear and circular

This video explains how light, as electromagnetic waves, can oscillate in specific directions, a phenomenon known as polarization. Dive into the distinctions between polarized and non-polarized light, and see how this concept plays a vital role in everyday items like sunglasses and 3D movies. Created by David SantoPietro.

## Want to join the conversation?

• How does the plastic sheet limit the polarity?
• It's a good idea if you don't consider it a plastic sheet. Consider it a crystal, with a sort of slit. A slit which only allows a wave oscillating in say an up-down manner to pass through. That said, all waves which conform to this arrangement make it through, no sweat. However, it is not necessary that all other waves are blocked. Some of them could have vector components which can conform to the arrangement, and those components go through. All in all, the intensity of the incident light goes down, but the result is polarized.
• Hey,
Why is the phenomena of "Polarization" focus so much importance to the orientation of electric field but not the magnetic field?
Isn't the magnetic field, the vertical component in an electromagnetic wave and the electric field is perpendicular to it?
Am I right?
Murtuza Abbas.
• Because it's often good enough just to know the direction of one of the fields. The other is always perpendicular to the first, thus making it easy to study phenomena like Polarization. Also, it gets messy while considering both of the fields. Why do it the hard way when you get the answer the easier way?
• So if I put 2 left-eye lenses from the 3D glasses in the same frames, would I see the movie in 2D without it being fuzzy?
• Yes I believe. Because the other image that makes it fuzzy would be completely blocked.
• Why is sky blue?
• That, sir, is a great question!
The sky is blue because of an effect called light scattering. Basically when light hits small particles, it spreads out. The particles in the atmosphere of the Earth have a size that mostly affects blue light. That is also the reason that makes the sun yellow (the blue is partially removed from the light of the sun).

• How do the 3d glasses create a circular polarization filter, and how do they select clockwise vs. counterclockwise?
• The glasses actually have 2 filters, one of which has two "slits" which let through light polarized in two directions, which, as explained in the video, will result in diagonal linear polarization. Then the second filter has a slit only with that one direction.

The other eye is the same way, except the first filter will create (because the light "spins" the other way) a diagonal polarization rotated by 90° compared to the first, and the second filter, again, lets through only that light.

It's hard to visualize, so here is a picture: http://en.wikipedia.org/wiki/File:Circular.Polarization.Circularly.Polarized.Light_Circular.Polarizer_Passing.Left.Handed.Helix.View.svg
• Regarding the E & B field, How the polarizer affect E&B field together? I saw the SEM image of polarizer and I understand how It works if only include E field into account. So if we have up&down polarizer, what will happen with the left&right B field? Will it get blocked too?
• For most materials, the magnetic permeability is extremely low, so there is almost no interaction between the magnetic field and the material. This means that it is not absorbed by the polarizer, and simply propagates with the associated E field.
• I can't understand the polarization
please explain it to me ?
• I liked my teacher's example with a mechanical wave in a rope. Picture you have a rope, and a piece of wood with a rectangular opening, just thin enough so the rope can slide vertically in the opening.
You secure the piece of wood and pass the rope through it, and secure the rope's far end in a wall or something, while holding the other end. At this configuration, you send waves in a random pattern and watch as they go through the rectangular opening.
http://soumaisenem.com.br/sites/default/files/onda23.jpg (got this image from a brazilian website aimed for university admission exams)
The waves will be polarized, which means that now they only oscillate in one direction.
For electromagnetic waves, since they are generated and propagate through the oscillation of electrons, a polarizer will allow the electrons to oscillate in only one direction (kinda like the rectangular opening of the rope and wood example). Thus, the wave will propagate oscillating only at that direction.
• please explain diffraction as a limit on resolving power. and what is resolving power of microscope and telescope
• Diffraction is the super position of waves coming from an infinite source across the width of the slit.Resolving power come into play only for objects like microscope ,telescope etc because the eye piece of these instruments act like the small slit that collects or gathers light from the infinite source say the sun.
Resolving power of the microscope is the reciprocal of the limit of resolution .Limit of resolution is the distance between two close objects which can be resolved when seen throgh a microscope.
RP=2n sinB/1.22*wavelength
n=refractive index;
sinB=semi vertical angle;
n*sinB is known as the numerical apperture

Resolving power of the telescope is the reciprocal of limit of angular resolution of seperation .Limit of angular resolution of seperation is the smallest angular seperation between two distant objects so that they appear just seperated when seen through a telescope.
RP=D/1.22*wavelength.
D=diameter of the objective