Material after quiz and still on everyone s Unit 11 test.

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Sheila Rose
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Material from here on out though is NOT on the final exam for seniors but IS on the final for nonseniors When light travels out of glass or water and back into

$Calculating the Critical Angle (CA) The CA is the angle of incidence that provides an angle of refraction of 90 o.$

1 Material after quiz and still on everyone s Unit 11 test. When light travels from a fast material like air into a slow material like glass, Snell s Law always works. Material from here on out though is NOT on the final exam for seniors but IS on the final for nonseniors When light travels out of glass or water and back into air, something unusual happens as the angle of incidence gets larger. Calculating the Critical Angle (CA) The CA is the angle of incidence that provides an angle of refraction of 90 o. Substituting into Snell s Law reveals that the CA can be calculated by taking the inverse sine of the ratio of the indices of refraction. The ratio of n r /n i is a value less than one. It has to be. This ratio must be less than one. Try it! Θcrit = sin -1 (n r /n i ) I won t be providing this equation. It can still be determined from Snell s law bc angle of refraction is 90 o, and you ll have both n s. What is the critical angle for water? 1

$incidence when refraction still occurs BUT If$ $angle, refraction no longer occurs.$ Instead the light is internally reflected!

reflection of all the incident light bounces

medium and approaching a less dense medium

socalled critical angle Will happen for light

2 The critical angle is the largest angle of incidence when refraction still occurs BUT If the angle of incidence exceeds the critical angle, refraction no longer occurs. Instead the light is internally reflected! Total Internal Reflection Occurs when the reflection of all the incident light bounces off the boundary Light is in the more dense medium and approaching a less dense medium Angle of incidence is greater than the socalled critical angle Will happen for light traveling from water to air, but not air to water Fish Tank TIR Fish View of the World 2

$Refraction$ Phenomena

3 Sparkling Diamond TIR and Fiber Optics Fiber Optics TIR and Prisms Interesting Refraction Phenomena Prisms, Rainbows, Mirages 3

Dispersion The separation of visible light into its

frequency and will bend varying amounts upon passage

the n value for frequencies of violet light is 1.

$different index of refraction, so each color bends a$ Rainbows To view a rainbow your back must be to the

4 Dispersion The separation of visible light into its different colors Each color has a distinct wave frequency and will bend varying amounts upon passage through a prism For instance for some types of glass, the n value for frequencies of violet light is 1.53; and the n value for frequencies of red light is ROYGBIV! Dispersion Each color of light has a slightly different index of refraction, so each color bends a different amount. Rainbows To view a rainbow your back must be to the sun as you look at approximated 40o above the ground with suspended droplets of water, even a mist. Each droplet then acts as a little prism Rainbows 4

Double Rainbow Double Rainbow https://youtu.

5 Double Rainbow Double Rainbow Structures of the Human Eye Human Eye Diagram (p500) Blind spot cards Look at your blood flowing through your eye! Why don t you normally see this? Refraction Structures Cornea (3/4) - fixed Lens (1/4) - adjustable 5

Common Disorders Cataract cloudy cornea, fixed with surgery. Glaucoma high pressure in eye fluid, fixed with medicine or surgery. Macular Degeneration leading cause of blindness over 50.

It is the second part of your eye, after the cornea, that helps to focus light and images on your retina.

The ciliary muscles, which are part of the ciliary body, are attached to the lens and contract or release to change the lens shape and curvature.

and therefore loses some of its ability to focus on near objects. This is called presbyopia and explains why people need reading glasses as they become older.

Most people are between 40 and 50 when they begin to realize that the letters of the telephone book are "too small" or that it's necessary to hold the newspaper further away in order to see clearly.

Near sightedness You can see near things: With myopia, you can see close-up objects clearly, but distant objects are blurred.

6 Common Disorders Cataract cloudy cornea, fixed with surgery. Glaucoma high pressure in eye fluid, fixed with medicine or surgery. Macular Degeneration leading cause of blindness over 50. Thinning and degeneration of the central part of the retina. The lens is composed of transparent, flexible tissue and is located directly behind the iris and the pupil. It is the second part of your eye, after the cornea, that helps to focus light and images on your retina. Because the lens is flexible and elastic, it can change its curved shape to focus on objects and people that are either nearby or at a distance. The ciliary muscles, which are part of the ciliary body, are attached to the lens and contract or release to change the lens shape and curvature. The lens becomes more rounded to focus on near objects (left pic) and more elongated (or stretched) to focus on objects that are far away (right pic) Over time, the lens loses some of its elasticity and therefore loses some of its ability to focus on near objects. This is called presbyopia and explains why people need reading glasses as they become older. Presbyopia Presbyopia makes it difficult to focus on close-up words or images. Most people are between 40 and 50 when they begin to realize that the letters of the telephone book are "too small" or that it's necessary to hold the newspaper further away in order to see clearly. At the same time, the ability to focus on objects that are far away remains intact. Near sightedness You can see near things: With myopia, you can see close-up objects clearly, but distant objects are blurred. Myopia occurs when the eyeball is too long for light rays to focus correctly on your retina. The more myopic you are, the blurrier your vision will be at a distance and objects will have to be closer to you in order to see them clearly. Far Sightedness Astigmatism With hyperopia, you can see distant objects clearly far things, but close-up objects are blurred. Hyperopia occurs when the eyeball is too short for light rays to focus correctly on your retina If you have astigmatism, it means that the surface of your eye (the cornea) is not smoothly curved; instead, the surface is irregular. Normally, the surface of your cornea is rounded, much like a basketball; with astigmatism, however, your cornea is shaped more a like a football (American football, that is). This doesn't allow light rays to focus clearly on a single point on your retina. Astigmatism is usually accompanied by myopia or hyperopia and is usually correctable with eyeglasses. 6

Corrective Lenses (what type of lens fixes what?

Light Are Light Waves Longitudinal or Transverse?

7 Corrective Lenses (what type of lens fixes what?) Good Lens and Cheap Lens Nearsightedness Farsightedness Astigmatism Polarization of Light Are Light Waves Longitudinal or Transverse? EM waves are caused by vibrating charged particles (often electrons). Light waves are transverse. The charged particles vibrate in a direction perpendicular to the direction of travel of the light wave. Unpolarized Light - A collection of waves from charges vibrating in many directions. The sun, a lamp in the classroom, a candle all emit unpolarized light. 7

Polaroid filters Unpolarized light passes through the filter and emerges with HALF the intensity and

8 Polarized light It is possible to polarize unpolarized light Three Ways to Polarize Light 1. Polarizing Filters selective absorption. Polaroid filters Unpolarized light passes through the filter and emerges with HALF the intensity and vibrations in a single plane Only vibrations parallel to the filter pass through Is it possible to polarize ALL of the light? Polarized Light Are the glasses really polarizing? 8

$2. Calcite double refraction$ Surface https://www.youtube.

9 2. Calcite double refraction 3. Reflection from Non-metal Surface ZJ9E Vertical Glare from Vertical Surfaces Adding a Filter to a Camera Light reflected off water is partially polarized in a direction parallel to the water s surface. Which direction is this filter polarized? Which way should sun glasses be made? 9

10 Which way should sun glasses be made? Glare is greatly reduced Non-reflective coating Put a coating which is the average between glass and air on your lens, so the amount of reflection is about equal for both mediumchanges. Destructive interference can occur completely for one wavelength, and partially for other nearby wavelengths. Often, coatings use 550 nm (right in the middle of visible spectrum). Red and violet are not usually affected, which is why people with glasses seem to have a certain glare associated with those colors. 10

In Summary: Polarized Light Polarized light lies

polarized because the electrons vibrate in random

Light that is not polarized can be polarized by a

Polarized Light Light that reflects at glancing

$the road? Light can also be polarized by refraction.$ $Both refracted light beams are polarized - one in a$

11 In Summary: Polarized Light Polarized light lies along the same plane as that of the vibrating electron that produced it. A vertically vibrating electron emits light that is vertically polarized. A horizontally vibrating electron emits horizontally polarized light. Common light sources emit light that is not polarized because the electrons vibrate in random directions. Light that is not polarized can be polarized by a polarizing filter. Polarized Light Light that reflects at glancing angles from nonmetallic surfaces vibrates mainly in the plane of the reflecting surface. Which pair of glasses would best block glare from the road? Light can also be polarized by refraction. the mineral calcite refracts incident light into two different paths. Both refracted light beams are polarized - one in a direction parallel to the surface and the other in a direction perpendicular to the surface. Polarized Light Light will pass through a pair of polarizing filters when their polarizing axes are aligned, but not when they are crossed at right angles. 11

12 Polarized Light and 3-D Viewing Vision in 3 dimensions depends on the fact that each eye views a scene from a slightly different angle. Slide shows or movies achieve a 3-D effect by projecting a pair of views that are polarized at right angles to each other. Polarizing eyeglasses ensure that each eye sees a separate picture. Sixty Symbols- How 3D Glasses work, very cool video on the use of polarization frn for most of the unit ht for polarization and double slit experiment Stop here for Spring 18 12

Refraction Phenomena Apparent Depth & Volume

$Refraction Phenomena Apparent Depth & Volume$ Refraction Phenomena Apparent Depth & Volume Refraction can change the perception of depth and volume because the apparent path of light does not equal the actual path of light. 1 Underwater Vision Atmospheric