SAT Physics Physical Optics - Polarization Of Light
SAT Physics Physical Optics - Polarization Of LightPOLARIZATION OF LIGHT
Light waves are electromagnetic waves consisting of both an oscillating electric field and an oscillating magnetic field. These two oscillations sustain each other and allow light to propagate independently, even through a vacuum. The electric field and magnetic field waves are both transverse waves where the oscillating fields are perpendicular to the direction of wave travel. In addition, the electric field oscillation is perpendicular to the magnetic field oscillation. Working with both of these perpendicular oscillations is complex. As a result, light waves are often simplified as a single transverse wave involving only the electric field oscillation.
Because the oscillating electric field occurs in a set plane, light waves are polarized. The poles of the oscillation are the crests and troughs of the electric field wave, which maintain their orientation as light waves propagate. The plane in which the electric field oscillates is known as the plane of polarization. In Figure 17.7, the electric field is oscillating in die x-y plane and this electromagnetic wave is polarized along the y-axis.
Figure 17.7. Electromagnetic wave
Light waves can be polarized in any direction. Light arriving from the Sun consists of countless waves, each polarized in random directions. When treated together, all of these random polarizations cancel each other. So the light from the Sun, as well as light from other conventional light sources, is unpolarized. The diagrams in Figure 17.8 are simplified by showing the polarization of light for two light waves coming directly out of the page. Figure 17.8(a) is polarized in the y-direction only. Figure 17.8(b) consists of waves polarized in a variety of directions and is an example of unpolarized light.
Figure 17.8. Polarized (a) and unpolarized (b) light
If unpolarized light passes through a polarizing filter, it will become polarized. A polarizing filter contains a transparent sheet imbedded with long, organic molecules oriented in only one direction. It is similar to the bars of a jail cell, where some things can pass through and others cannot. Only the light rays oscillating in one direction will pass through the polarizing filter. Light oscillating in all other directions is blocked.
Unfortunately, polarization is often shown incorrectly in diagrams in order to simplify the concept for beginning students. Figure 17.9 is the simplified, incorrect example. It shows unpolarized light passing through a polarizing filter where the organic molecules are aligned in the y-direction.
Figure 17.9. Simplified but incorrect example of polarization
This transfer of energy absorbs the light polarized in the direction matching the alignment of the organic molecules. The light that actually transmits through the filter is the light perpendicular to the strands of organic molecules, as shown in Figure 17.10.
Figure 17.10 Correct example of polarization light
Exams are more likely to focus on the fact that a single polarizing filter allows light waves oscillating in only one direction to pass through. You should also note that this phenomenon experimentally demonstrates that light is a transverse wave. In addition, exams will often test the effect of two polarizing filters used together, as shown in Figure 17.11.
Figure 17.11. Effect of two polarizing filters
When two polarizing filters have the same orientation, light is polarized in the same manner as if only one filter is present. When two polarizing filters are perpendicular, they block all waves in any orientation. No light passes through. If the filters start in the position shown in Figure 17.11(a) and one filter is turned about the axis of propagation, the light passing through will become dimmer and dimmer. When the filter has turned 90°, all light will be blocked. Polarizing filters are used in 3-D glasses to view movies. A 3-D movie is actually two polarized movies superimposed on the screen. One lens of the 3-D glass allows vertically polarized light to pass through, and the other lens allows horizontally polarized light to pass through. Each eye is watching a different movie. The brain interprets the resulting images as three dimensional.
Light reflecting off of surfaces is partially polarized. The direction of this polarization matches the surface from which the light is reflected. When sunlight reflects off of the ocean, lakes, and the hoods of cars, it is slightly polarized in the horizontal direction. This type of polarization is commonly referred to as reflected glare. Polarized sunglasses are actually polarizing filters oriented to block this horizontally polarized reflected glare.
Visible light consists of the colors extending from red to violet in the electromagnetic spectrum. In order to see specific colors, light waves must be aimed at and enter the eye in order to stimulate the photoreceptors in the retina. There are two ways to see light. Either a beam of light is shined directly into the eye from a light source, or light can reflect off of a surface and then enter the eye. If a light source is red, an observer will see red. However, the reflection of light is more complicated.
Absorption and Reflection
When light strikes a surface, some wavelengths will be absorbed and others will reflect. If light is absorbed, it cannot be seen. Only the reflected rays bouncing off of an object are capable of entering the human eye. When objects are observed with the eye, the reflected colors are seen. For example, think of green leaves. Leaves reflect the wavelengths of light that appear green. This means that other wavelengths of light are being absorbed. Leaves absorb the wavelengths consistent with red and blue light, which are the wavelengths needed for photosynthesis.
White light arriving from the Sun is composed of all the wavelengths of visible light. These wavelengths can be separated into distinct colors of light through a process known as dispersion. This process is commonly demonstrated using a prism. Dispersion takes advantage of both refraction and geometric optics. When white light strikes a prism at an angle, the light separates (disperses) into individual colors. Each wavelength (color) of light has a slightly different wavelength and index of refraction when it moves through the prism. As a result, each color bends at a slightly different angle as it enters and leaves the prism, as shown in Figure 17.12. The short wavelengths of light (violet and blue) have the highest index of refraction. So they bend the most. All the colors of the spectrum are separated. A rainbow effect is seen that extends from red to violet.
Figure 17.12. Dispersion of light through a triangular prism
When light rays in the atmosphere strike particles in the air, the light rays are reflected in various directions. This process is known as scattering. Shorter wavelengths of light are scattered the most. The blue light is reflected off the particles in the air and enters the eye, giving the sky its blue appearance.
Thanks for sharing such a nice article. It is really useful to me and all people. One thing in my mind came while reading that it is not wasting of time. currency exchange app shopify , currency converter box free online , best shopify apps to boost sales in 2019ReplyDelete
I guess you are a smart cookie because of your knowledge and insight. The articles brings some advice. I learn more from them. Please update more posts. I usually read them. Thank you very much.sale discount app on Shopify , Product discount master , best shopify free apps to boost sales in 2019ReplyDelete
Thanks for such a pleasant post. This post loaded with lots of useful information. Keep it up. If you are looking for the best information and suggestions related to O Level Physics Tuition then visit Tuition Solution.ReplyDelete
I read all the information you have mentioned in your blog that is really commendable. I really like your post, please share more information with us.ReplyDelete
leaving cert physics notes
Thanks for such a amazing post. This post is filled with lots of useful information. Keep up the good work.ReplyDelete
IELTS training in noida
I read your post and got it quite informative. I couldn't find any knowledge on this matter prior to. I would like to thanks for sharing this article here. home tutorReplyDelete
Really glad to say, your post is very interesting to read. I never stop myself to say anything about it. You are doing a great job. Thank you for sharing this blog hereReplyDelete
Online Schooling For High School In India
I am very thankful to you for sharing this best knowledge. This information is helpful for everyone. So please always share this kind of knowledge. Thanks. 1000 Watt Metal Halide Led ReplacementReplyDelete
Remarkable post. I simply came across your blog and desired to say that I have really enjoyed searching your blog posts. Thank you for sharing such blogs. 480v single phase led lightingReplyDelete
I agree with a lot of the points you made in this article. If you are looking for the Higher Chinese, then visit Chinese Distinction. I appreciate the work you have put into this and hope you continue writing on this subject.ReplyDelete
Great article by the great author, it is very massive and informative but still preaches the way to sounds like that it has some beautiful thoughts described so I really appreciate this article. Best physics home tuition bhopal service provider.ReplyDelete
You have a real ability to write a content that is helpful for us. Thank you for your efforts in sharing such blogs to us. black churches in atlanta georgiaReplyDelete
This comment has been removed by the author.ReplyDelete
This comment has been removed by the author.ReplyDelete
Your contents are completely awesome and share worthy. I really appreciate your efforts that you put on this. Keep sharing. For more Tutoring Catherine Fields related information visit Sprouts AcademyReplyDelete
I am attracted by the info which you have provided in the above post about light. It is genuinely good and beneficial info for us. Continue posting, Thank you. green underwater lightsReplyDelete
This comment has been removed by the author.ReplyDelete
Hey what a brilliant post I have come across and believe me I have been searching out for this similar kind of post for past a week and hardly came across this. Thank you very much and will look for more postings from you Best how to start learning mandarin service provider.ReplyDelete
You've written a very useful article. This article provided me with some useful knowledge. Thank you for providing this information. Keep up the good work. Led Light Company in DubaiReplyDelete
The delightful article you have posted here. This is a good way to increase our knowledge.Glass manufacturer Continue sharing this kind of articles, Thank you.ReplyDelete
Nice info, I am very thankful to you for sharing this important knowledge. This information is helpful for everyone. Read more info about Private Tutors Adelaide. So please always share this kind of information. Thanks.ReplyDelete
This article contains a lot of critical information. I'm dazed by the idea of the information and moreover it is a useful article for us, Gratitude for share it.Tutoring Services In PflugervilleReplyDelete