Question 1: What is the relationship between electric ...



Student Responses to Reading Quiz #16, due Wednesday March 10

Question 1: The book discusses some interesting applications to or explanations of physical phenomena (for example fiber optics, mirages, prisms, rainbows, etc.) using the ideas of refraction. Pick the one you think is most interesting and briefly explain the phenomena using these ideas.

1. If light travels through a bunch of fibers at an angle approximately parallel to the fibers, the light will total internally refract through the and come out the other end. This holds as long as the fibers are not bent at too sharp of an angle.

2. Fiber optics uses the principle of total internal reflection in order to transmit light down a long and narrow fiber that is curved. The light beam will hit the curved wall with an angle greater than the critical angle so there will be no refracted ray, just a reflected ray. This process continues throughout the entire fiber. You wouldn't think you would be able to have light travel in a circular path but in lab we saw it could travel in a narrow glass tube that was circular and then it would come out the other side. I thought that was pretty cool.

3. I think mirages are most interesting, because the "wet spots" that disappear have always really annoyed me when I drive because I never really understood them. These mirages are due to the warm layer of air near the ground. Warmer air is less dense, so the speed of light near the ground is slightly greater, and light bends as it goes from the cooler to warmer layer. This causes the person watching to see an image that appears to be reflected off of water as well as the actual image.

4. When light enters a fiber obtic cable parallel to the axis of the cable, the cable can bend and loop and the light will always experiences total internal reflection. This is because the light is slower inside the cable than in the air. It allows for imformation to be sent at much greater speeds because the frequency of light is so high.

5. Prism: White lite entering a prism is dispersed into rainbow colors. Explain: The index of refraction of the prism changes slightly to different wavelengths. Shorter wavelengths bend more (so violet bends the most, red bends the least)

6. Fiber optics sends light down narrow glass tubes, this kight hits the sides at an angle that is bigger than the critical angle, so the information travels near the speed of light down the tubes.

7. fiber optics work on the pricipal that the light entering nearly parallel to the axis of the fiber will experience total internal reflection. this allows the light to travel all the way down the length of the fiber despite bends in it.

8. I think mirages are pretty cool. They are created because on hot days the air near the ground is slightly warmer and less dense than the air above it. As a result, the index of refraction is different and the light is bent. This can make light that originates in high spots (like the sky or a tree) appear to originate from the ground.

9. In fiber optics, a thin strand of glass fibers are used. Light enters into one end of the strand and is reflected off the interior sides until it comes out the other end. Because the fibers have such a small diameter, the light in it is esentially parallel to the sides. The light never reaches an angle where it cam be refraced.

10. In fiber optics, information is transferred at very high rates via light beams travelling through long, narrow glass fibers. The light is essentially trapped in the fibers until it reaches the end due to total internal reflection, in which all incident light is reflected back into the incident medium and none is refracted out into the adjacent medium.

11. The index of refraction of water depends slightly on the wavelength of light, which causes the separation of the colors in the rainbow as well as the the characteristic of the angular radius of the bow. The rainbow is made of light waves through many droplets of water. The color seen at each angular radius corresponds to the wavelength of light that allows the light to reach your eye from the droplets at that angular radius. Because the index of refraction of water is smaller for larger wavelengths, red is at a slightly great angular radius than the blue is in a rainbow.

12. I've always thought mirages were very cool. Mirages are usually formed on hot days when the air near the ground has a lower index of refraction than the air higher up due to heat from the ground. this causes rays of light to bend gradually towards the eye, making it seem like an object exists where it actually does not.

13. Fiber optics work when the critical angle is very small, meaning most of the light stays inside the fibers. Most of the light then exits out the end of the fiber.

14. Fiber optic lines are very interesting to me. They act as pipes but for light instead of water. The lines are very very thin and have an index of refraction very close to one, this causes light going through the lines to always reflect back into the line (when they work perfectly). Fiber optics are really amazing and I think and revolutionizing the world. Imagine being able to send 1,000 Giga bytes of data across the US in less then a second...

15. Fiberoptics utilizes total internal reflection to transmit data from one end of a glass wire to another. Because the index of refraction of the glass is greater than the index of the surrounding air, it allows the cirtical angle of reflection to be much less, so the signal can "bend " through the pipe.

16. I think that mirages are very cool. Mirages are caused by a layer of air close to the ground that is warmer than the surrounding air. This air refracts the light as it passes through, bending it upwards. When the light enters your eye, it looks as if it is coming from the ground and you see a reflection of the object being observed.

17. rainbows are pretty and neat - the way water droplets split the light in such a huge way is amazing

Question 2: Two polarizing filters are set up so that their transmission axes are perpendicular to each other. Explain, using ideas of electromagnetic radiation and re-radiation, why little to no light would be transmitted through this filtering set-up.

1. If the transmission axes are perpendicular, the electric field affecting the light will cancel out the EM wave of light due to destructive interference (not sure)

2. Light is an electromagnetic wave that has perpendicular electric and magnetic fields. If we set up two polarizing filters perpendicular to each other, the first being the polarizer and the second the analyzer then little to no light would be transmitted. This occurs because when light is passed through the polarizer only the light incoming parallel to the polarizer will pass through. However the analyzer is oriented 90 degrees different so none of this light is parallel to the analyzer so it will not pass through at all.

3. The part of the electric field that is parallel to the transmission axis light is transmitted through the polarizing filter, and the perpendicular part is absorbed. Therefore, when two filters are set up with their axes perpendicular, only the light parallel to the first one makes it through the first filter, and then all of this light is absorbed by the second filter since the first filter (and thus the transmitted light) is perpendicular to it. This is consistent with Malus's law, because in this case theta=90, and the cosine of 90 is zero.

4. When unpolarized light hits the first of the two polarizing plates, all the electric field components that are not perpendicular to the transmission axis are absorbed. The light is now polarized and continues on. When the electric waves strike the next plate, they are incident to the tranmission axis and are absorbed also.

5. Through the first filter, only E paralell to the transmission axis of the first filter gets through. This E has no component paralell to the axis of the second filter. So no light gets through

6. The E field is perpendclar to the filters, so the light is traveling though the filters and is almost all absorbed.

7. the radiation that is not paralell with the axis of polarization of the first lens is abosorbed, and so only radiation oriented in a specific way gets passed to the second filter. since the axis of the second is perpandicular it absorbs all of the radiation it receives from the second

8. The light that is incident on the first polarizing filter has components of its electric field in both the x and y directions. Assume that the first filter is aligned with the y-axis. Now only light that has an electric parallel to the y-axis will pass through the filter. When it reaches the polarizer that is aligned with x-axis there will no longer be any electric fields aligned in that direction, so no light will pass through. In terms of radiation and re-radiation, there must be a conductor in the material. The electric field from the light will create a current in this conductor. So, all the light that has an electric field component parallel to the conductor will be absorbed. The rest of the light is transmitted. The light that is absorbed is reradiated, which causes a reflection.

9. When light travels through the first polarizing filter that polarizes light in the verticle direction, about half of the light will be absorbed. The other half will be in the verticle plane. When the second filter that polarizes light in the horizontal direction, is placed behind the first filter, it will block all the light in the vertical direction. Since the light from the first filter is in the verticle direction, all of it will be absorbed by the second filter.

10. Assume the light is travelling in the z direction, the polarizing filters lie in the x-y plane, and the transmission axes of the filters coincide with the x and y axes. If the light first travels through the filter whose transmission axis is along the x axis, the y component of the oscillating electric field passing through the filter will be eliminated, leaving only the x component. When the electric field comes to the second filter, which has a transmission axis along the y axis, the x component of the electric field will be eliminated. Because both the x and y components of the electric field have been eliminated, no light is transmitted through the second filter.

11. Little or no light would show through two polarizing films when their transmission axes are perpendicular because the intensity of the light on the second polarizing film depends on the angle between the transmission axeses such that I=Iocos^2(theta). When the setup is at a 90 degree angle, the intensity, as calculated from this equation, would be zero.

12. All the light is transmitted when the electric field is parallel to the transmission axis and all is absorbed when it is perpendicular to the transmission axis.

13. If both axis are perpedicular to each other, then the half of the light in the x direction is filtered and the other half in the y-axis is also filtered, leaving no light seen.

14. If the transmission axes are perpendicular to each other they interfere in a destructive manner so most to all the light is disappated.

15. The first polarizer would "weed out" say all the vertically oriented waves (re-radiatin horizonal waves), then the second would weed out all of the horizontal waves. Afterwhich, there would be no waves left.

16. When the radiation passes through the first polarizing filter, it blocks out all the light that is not vibrating in one plane. The second polarizing filter blocks out all the radiation that is vibrating in the direction allowed by the first filter, but allows radiation that is perpendicular to the first polarization. Some light comes from outside sources that don't pass through both filters, so some light gets through.

17. Little light would be transferred because the first polarizing lens would only allow light waves propigating in one direction through. The other lens would only allow waves propagating in a different direction through that wouldnt match the first one

Question 3: What are the conceptual and mathematical issues from the reading that you would like to discuss in class?'

1. I do not understand the polarization chapter well, an explantion will be helpful

2. All the different polarization methods were confusing.

3. can't think of anything

4.

5. Physical mechanism for reflection and refraction (page 1043) What does it mean by polarization of light? Polarization by Scattering Polarization by BireFringence

6.

7.

8.

9.

10. The cause of dispersion

11.

12.

13. Polarization by Reflection

14. polarization and transmission axes

15.

16. none

17. nope

Question 4: What concerns or issues do you still have with material from previous classes?

1. I still have some issues with the material in chapter 35, when i get a chance i will probably stop by your office to ask question. I am not sure when this will be

2. None

3. i think i'm ok

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5.

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9.

10. None

11.

12.

13. I'm still having difficulties with the assigned problems and such from the previous material. (chap 35)

14. still having some trouble some of the problems that deal with minima or maxima at multiple wavelengths, like number 82 for the hand ins.

15.

16. none

17. none

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