Mirror Image: Reflection and Refraction of Light Mirror Image: Reflection and Refraction of Light By Jim Lucas, Live Science Contributor | October 1, 2014 10:43pm ET MORE A mirror image is the result of light rays bounding off a reflective surface. Credit: Denys Kurbatov | Shutterstock When people look into a mirror, they see an image of themselves behind the glass. That image results from light rays encountering the shiny surface and bouncing back, or reflecting, providing a "mirror image." People commonly think of the reflection as being reversed left to right; however, this is a misconception. If you face north and look straight into a mirror, the east side of your face is still on the east side of the image, and the same is true for the west side. The mirror does not reverse the image left to right; it reverses it front to back. For example, if you are facing north, your reflection is facing south. The reflection of light rays is one of the major aspects of geometric optics; the other is refraction, or the bending of light rays.

Geometric optics is one of two broad classes of optics, the field that "deals with the propagation of light through transparent media," according to Richard Fitzpatrick, a professor of physics at the University of Texas at Austin, in lecture notes for a course in Electromagnetism and Optics . (The other class is physical optics.) Geometric optics Geometric optics treats light as continuous rays (as opposed to waves or particles) that move through transparent media according to three laws. The first law states that light rays move through similar transparent media in straight lines. The second states that when a light ray encounters a smooth, shiny (or conducting) surface, such as a mirror , the ray bounces off that surface. The third law governs how light rays behave when they pass between two different media, such as air and water. For example, when you look at a spoon in a glass of water, the submerged part of the spoon appears to be in a different place than expected. This happens because the light rays change direction when they go from one transparent material (air) into another (water).

Sir Isaac Newton laid down the foundation for geometrical optics in his classic 1704 work " Opticks ." The principles he described are still used to this day to design eyeglasses, telescopes, microscopes, eyeglasses and camera lenses. In a reflecting telescope, light strikes the primary mirror and bounces back to a secondary mirror, which diverts the light to the lens in the eyepiece. Credit: Virginia Commonwealth University Reflection Reflections from flat surfaces are fairly easy to understand. A reflection appears to be the same distance from the "other side" of the mirror as the viewer's eyes are from the mirror. Also, when light is reflected from a mirror, it bounces off at the same angle in the opposite direction from which it hit. For example, if the light hits a flat or "plane mirror" at a 30-degree angle from the left, it will bounce off at a 30-degree angle to the right. However, if the surface of the mirror is curved, the angles of reflection are different at different points on the surface. The most common curved surface used in optical devices is a spherical mirror .

If the mirror is convex, or curved outward, it will reflect a wider area, in which images appear smaller and farther away than those from a flat mirror. These mirrors are often used for outside rearview mirrors on cars and for keeping large areas under surveillance in stores. If the surface is concave, or curved inward, a group of light rays from a distant source is reflected back toward a single location known as the focal point. This generally produces a magnifying effect, such as that seen in a makeup mirror. The radius of curvature of a mirror determines its magnification factor and its focal length. Newton used a concave spherical mirror to make his reflecting telescope , a design that is still popular with amateur astronomers due to its simplicity, low cost and high degree of image quality. In a Newtonian reflecting telescope, light rays from distant objects, which are essentially parallel (because they come from so far away), strike the concave main mirror at the same angle. The rays are then reflected back up through the telescope tube toward the focal point. However, before they reach the focal point, they strike a secondary, flat mirror that is tilted at a 45-degree angle. The secondary mirror diverts the light out through a hole in the side of the tube.

The eyepiece lens then focuses the light. This produces a magnified image. Also, the image appears much brighter than it does to the naked eye because the mirror gathers and concentrates the light. The shape of a spherical mirror affects the image that is reflected. Light striking near the edge of the mirror does not focus at the exact same spot as light striking nearer to the center. This results in what is called spherical aberration. This phenomenon is often corrected by using a combination of lenses, or in the case of large telescopes, by using parabolic mirrors, which are shaped like rounded cones that focus all the light from a source to a single point. A "bent" spoon in a glass of water is an example of refraction. Credit: Crok Photography Shutterstock Refraction Refraction is the bending of light rays. Normally, light travels in a straight line, and changes direction and speed when it passes from one transparent medium to another, such as from air into glass. In a vacuum, the speed of light , denoted as "c," is constant. However, when light encounters a transparent material, it slows down.

The degree to which a material causes light to slow down is called that material's refractive index, denoted as "n." According to Physics.info , approximate values of n for common materials are: Vacuum = 1 (by definition) Air = 1.0003 (at standard temperature and pressure) Water = 1.33 (at 68 degrees Fahrenheit or 20 degrees Celsius) Soda-lime crown glass = 1.51 71-percent lead flint glass = 1.89 Cubic zirconia = 2.17 Diamond = 2.42 These numbers mean that the speed of light is 1.33 times slower in water and 2.42 times slower in diamond than in a vacuum. When light passes from a region of lower n, such as air, through a surface into a region of higher n, such as glass, the light changes direction. This means its path is closer to perpendicular, or "normal," to the surface. When the light passes from a region of higher n to the region of lower n, it bends away from the "normal" direction.

This is what causes the submerged part of a spoon in a glass of water to appear to bend when you put it in water. Focus In a lens with a curved surface, parallel rays bend at different angles depending on the angle of the surface where the rays enter the lens. Parallel rays entering a convex lens converge on a point on the other side of the lens. However, when parallel rays enter a concave lens, they diverge, or spread out, on the other side of the lens. They are said to have a "virtual focal point" at the spot where the diverging rays would meet if they were extended backward to the near side of the lens. Lenses can also be formed with a cylindrical surface, either convex or concave, which will magnify or reduce, respectively, an image in only one direction. These lenses are often combined with a spherical shape to produce a toric or spherocylinder lens. Such a lens is shaped like the surface of an inner tube, i.e., it has more curvature in one direction than another.

This shape is commonly used in eyeglasses to correct for astigmatism , a condition that causes blurred vision due either to the irregular shape of the cornea, the clear front cover of the eye, or sometimes the curvature of the lens inside the eye, according to the American Optometric Association. If you hold a pair of these eyeglasses away from your face and look through one lens as you rotate it, the astigmatic lens will cause the image to change shape. Geometric optics does not cover all areas of optics, however. Physical optics covers topics such as diffraction, polarization, interference and various types of scattering. Quantum optics addresses the behavior and property of photons, including spontaneous emission, stimulated emission (the principle behind lasers) and wave/particle duality. Jim Lucas is a freelance writer and editor specializing in physics, astronomy and engineering. He is general manager of Lucas Technologies . Readings - Light: Refraction of light Refraction If you shine a beam of light (a bundle of parallel rays) through the air, it will travel in a straight line. Rays of light usually travel in straight lines until they hit something.

If a ray of light hits the surface of a sheet of glass, some light will be reflected by the surface of the glass. However, much of the light will pass through the glass, because glass is transparent. Water affects light rays in a similar way. Some light will be reflected off the surface of the water, but much of the light will pass through the transparent water. When a ray passes from air into glass the direction in which the light ray is travelling changes. The light ray appears to bend as it as it passes through the surface of the glass. When a light ray passes from air into water a similar thing occurs: the light ray is bent as it strikes the surface of the water. This 'bending of a ray of light' when it passes from one substance into another substance is called refraction. The bending of a ray of light also occurs when the ray comes out of glass or water and passes into air. What causes this bending? Glass and water are thicker and heavier than air. They are said to be 'denser' than air. What happens is that light slows down when it passes from the less dense air into the denser glass or water. This slowing down of the ray of light also causes the ray of light to change direction.

It is the change in the speed of the light that causes refraction. This is a bit like when a car goes partly off the road and some of the wheels go into the softer edge of the road. The softer surface drags on the wheels and slows them down. This can cause the car to pull to the left, slightly changing its direction. Direction of bending When a ray of light passes from a less dense material (eg air) into a denser material (eg glass or water) it is bent away from the surface between the two materials. This means that in this situation the angle of refraction is always less than the angle of incidence. However, if the ray of light hits the surface at right angles (ie at 90°) to the surface, the ray is not bent. When a ray of light passes from a denser material (eg water or glass) into a less dense material (eg air) it is bent towards the surface between the two materials. This means that in this situation the angle of refraction is always greater than the angle of incidence. You can apply these rules for the refraction of light to any prism, triangular or rectangular. They also apply to light passing through lenses.

Refraction with lenses The bending of a ray of light also occurs when light passes into and out of a glass lens. However, because of the curved surfaces of the lens, the bending causes the light rays in a beam either to come together (converge, picture on left-hand side) or to spread out (diverge, picture on right-hand side). Because a convex lens can cause rays of light to converge, it can produce an image on a screen. This is called focusing an image onto a screen (a real image). The concave lens spreads the light rays out and so it cannot focus an image onto a screen. © Commonwealth of Australia, 2003 Refraction Refraction Introduction For thousands of years, people have noticed that a straight stick placed obliquely in water appears to be broken at an angle where it enters the water. This is the origin of the term “refraction,” which means literally “broken back.” For about two thousand years, astronomers have known that heavenly bodies seen near the horizon appear slightly higher in the sky than they really are. This was attributed to refraction by the Earth's atmosphere; but it was not understood in detail until a couple of hundred years ago.

This astronomical refraction, in its more extreme forms, is the cause of green flashes. Refraction in the atmosphere is complicated by the continuous change in density of the air. So let's begin by considering refraction of light at a plane boundary between two uniform media — say, air and water, or air and glass. (For the moment, we will ignore the variations of density in the air.) In the diagrams below, heavy lines represent “rays” of light. If you are not familiar with this conceptual fiction, please check the Optics for Beginners page before continuing here. The Basics When a ray of light passes from one transparent material (say, air) into a different material (say, glass, or water), its direction changes; e.g., <— water vs. glass —> The change in direction of the ray (represented by the heavy line in each diagram) is what is meant by the term refraction, which just means “bending” or “breaking.” By the way, the diagrams here don't indicate which way the light is moving along the ray (from upper left to lower right, or from lower right to upper left). That's because the light follows the same path, no matter which way it goes.

We often say “light rays are reversible” to summarize this property. How Much? Comparison of the two diagrams above shows that the ray is refracted more on entering glass than on entering water. We'd like to have a numerical measure of the refraction at the interface between two transparent media; then we could compare the relative refracting abilities of (say) glass and water. But the change in direction at the interface depends on the angle at which the ray meets the surface that separates the media. You can see from symmetry that if the ray is perpendicular to the surface on one side, it will still be perpendicular to the surface on the other; then there is no bending. As the rays become more oblique, the change in direction at the interface increases. So we need a quantitative description of the bending that separates the angular effects from the material properties. The law of refraction The actual law of refraction was discovered in the early 1600s by a Dutch mathematician and geodesist, Willebrord Snel van Royen . (Because his name in Latin is “Snellius”, the law is often called “Snell's law” instead of “Snel's law”.

You can find more information about Snel at the website of the Galileo Project . ) Snel found that there is a fixed ratio of two lengths in diagrams like those above. Let a ray of sunlight SR be incident on a rectangular tank of water, as shown below, where it is refracted at R. Extend the incident ray to A, on the vertical wall of the tank. Then the length of the actual refracted ray RC bears a fixed ratio to the extrapolated length RA, regardless of the angle of incidence. This ratio, RC/RA, is called the index of refraction, and denoted by the letter n. It is a property of the two media on either side of the refracting surface. For water and air, the ratio is very nearly 4/3; for glass and air, it is close to 3/2. (It's just a coincidence that the refractive indices of these common materials are so close to simple ratios; but it makes them easy to remember.) It is convenient to assign every material an absolute value of the index of refraction, instead of dealing with a “relative index” that depends on the second material (air, in these examples).

If we assign an absolute index of unity to vacuum, the index for air turns out to be nearly 1.0003 under ordinary conditions; then the absolute indices for most materials are very close to their relative indices, measured against air. So the index of refraction of water is about 1.33, and that of glass is about 1.5. Analytical treatment Of course, Snel's treatment of the problem is geometrical. If you know trigonometry, you can see that the ratio of the horizontal length RH to the diagonal RA is just the sine of the angle RAH, which is equal to the angle of incidence i measured from the line drawn perpendicular to the refracting surface at R. Likewise, the ratio RH/RC is just the sine of the angle of refraction RCH, or r. So Snel's ratio RC/RA is the same as (sin i)/(sin r). Consequently, the law of refraction is usually written as sin i = n sin r these days, where n is the refractive index. Interactive demonstration There is a nice interactive demonstration of the angular behavior of Snel's law in Fig. 3 on a commercial website.

When you move the light source (at the right side of that diagram), pay particular attention to how quickly the ray in air moves when it is nearly horizontal, and the source is under water. This extreme sensitivity near grazing incidence is the key to understanding how small variations in the refractive index of air can produce the spectacular effects of mirages and green flashes. Funny Business near Grazing Incidence This behavior near grazing incidence is so important for mirages and low-Sun phenomena that it deserves a closer look. Here's a plot of the angle in air against the angle in the water (both measured from the normal to the surface, remember; so grazing incidence means the angle in air is near 90°). See that little hook at the upper right end of the curve? At the very end, the curve becomes vertical; a tiny change in angle in the water corresponds to a very appreciable change in the angle in air. You might think that this wouldn't happen with the much smaller refraction of air (n = 1.0003) against vacuum (n = 1 exactly).

After all, air is about a thousand times less dense than water, and the refractivity (n − 1) of air (0.0003) is about a thousand times less than that of water (0.33). But take a look (note that the scale is magnified somewhat compared to the plot above): The curved part is only about half a degree here, as opposed to 10° or so for water in the previous plot. But there's still a hook, and the curve still becomes vertical at the end of it. Why doesn't the size of these angular effects scale with refractivity? Well, remember that we are dealing with the sines of angles near 90°, which is the same as saying, “the cosines of angles near zero.” Those who have had calculus will recall that, for small angles x (in radians), so that Now, suppose we continue to put the angle i on the low-index side of the surface between the two media — i.e., in the vacuum in this case.

Combine Snel's law sin i = n sin r with i = 90° − x so that sin i = cos x and play the same game with r that we just did with i: if the deviation of r from 90° is y, then Snel's law becomes cos x = n cos y where both x and y, the angles the rays make with the surface (instead of with its normal), are small. Now use the small-angle approximation discussed above, which gives 1 − x2/2 = n (1− y2/2 ) or n y2/2 − x2/2 = (n−1) . Now let the incident ray be grazing; that is, let x = 0. Then n y2/2 = (n−1) . But, as n differs from unity by less than 3 × 10−4, we may as well replace the factor of n on the left side by unity. Then, solving for y, we find y = [ 2 (n−1) ]1/2 .

That means that, even for two layers of air whose temperatures differ by one degree, so that the difference in n is only 10−6, y is 1.4 × 10−3 radian, or about 4.2 minutes of arc — more than an eighth of the Sun's angular diameter. And, as the refraction at grazing incidence is proportional to the square root of the temperature difference of the layers, we see that even temperature differences of less than a tenth of a degree will produce refraction effects easily visible to the naked eye. This shows why the small temperature differences between adjacent layers of air can have such obvious effects on the shape of the setting Sun, in spite of their very small differences in index of refraction. On the other hand, these appreciable effects occur only very near the horizon, where the angle of incidence is really grazing. [More precisely, the term x2/2 must be small compared to (n−1) to get these large effects, so that it can be regarded as “negligible” and dropped, as we did above.] If the layers of air are very nearly horizontal, then only very nearly horizontal rays will experience these marked effects.

That is why mirages and green flashes are observed only at (and below) the astronomical horizon: the rays have to be horizontal somewhere if they are to display these large effects. Calculating atmospheric refraction All the discussion above deals with plane surfaces. But the Earth isn't flat! To deal with refraction in a curved atmosphere, we have to introduce some geometrical considerations, which have been put on a separate page . Likewise, the atmosphere doesn't contain separate layers of different refractive index. The ray bending produced by a continuous distribution of density is discussed on another page . If you're not interested in the details of the calculation, but still want to know more about the refraction of astronomical objects by the atmosphere, see the page on astronomical refraction . Copyright © 2002 – 2012 Andrew T. Young Go back to the ... Compare And Contrast Reflection And Refraction Compare And Contrast Reflection And Refraction Compare and contrast reflection and refraction? science giorgiana1976 | College Teacher | (Level 3) Valedictorian Posted on February 24, 2010 at 3:11 AM Refraction is changing of light direction when crossing from a transparent medium to another.

Because light travels with different speeds in different environments, it has to change the speed at passing from one medium to another.If a beam of light reaches the surface at an angle, then the light on the beam side,which is reaching first the surface of separation, is forced to slow or to increase their speed before the light of the other side to reach the new environment.This causes bending, or refraction of the beam at separation surface. For example light reflected by an object under water passes first through the water and then by air to reach the eye of an observer. From some angles,a partially submerged object appears bent where it enters in water, because light coming from under the water is refracted. Refractive index of an environment is the ratio between velocity light in vacuum and the speed of light in that environment. Reflection also occurs when light reaches the surface of separation between two environments .Some of the light that reaches the surface of separation will be reflected in the first environment.

If the light reaches separation surface at an angle, then the light is reflected on the same angle, similar how to a ball jumps when it reaches the ground.Light that is reflected from a flat surface, such as surface between air and a lake, will form a mirror image.Light reflected from a curve surface can be focused in a point, a line, or in an area, so depending on the curvature of the surface. like 2 dislike 0 February 23, 2010 at 11:18 AM When light passes from from one type of medium to another type of medium, the medium being composed of substances like air, glass or water, one or both of two different types of changes take place in the direction of the ray of light as it strikes the surface separating the two mediums. These changes in direction of light are called reflection and refraction. Part of the light may not enter the new medium at all. Instead it may bounce back in original medium. This change in direction of light within a medium without entering another medium is called reflection. In the process of refraction the light enters from one medium to another instead of being bounced of the surface.

When this happens the direction of the light changes to some extent, but not completely reversed. The exact degree and orientation of change in direction depends on the angle at which the ray strikes the surface separating the two mediums and the comparative refractive indices of the two medium. As can be seen from the description above in case of reflection the light continues to travel in the original medium. In case of refraction the light travels from one kind of medium in to another. In case of reflection the angle the original ray of light makes with the the normal to the reflecting surface is equal to the angle made bu reflected surface although on the other side of normal. In contrast in case of reflection the angles with the normal made by original and refracted ray are different. In case of refraction there is no change in direction of light that strikes the refracting surface at right angle. In case of reflection the direction of original and reflected light is exactly opposite when the striking the reflecting surface at right angles. like 2 dislike 0 August 14, 2015 at 12:59 PM All light waves can be reflected and refracted. Reflection is when light is "bounced off" a shiny surface , e.g. a mirror.

The normal is at 90degrees to the surface. The light ray hitting the surface is known as incident Ray and the angle between the Incident Ray and the normal is known as the angle of incidence. The ray that is reflected from the mirror is known as the reflected Ray. The angle between the normal and the reflected Ray is known as the angle of reflection. For a plane (flat) mirror, the angle of incidence is equal to the angle of reflection. Refraction is the bending of light when light travels from one medium to another. Refraction occurs because the speed of the wave changes as it passes through different medium. If light travels from a less dense medium to a more dense medium, (from air into glass), the the speed of the light slows down. The angle between the incident Ray and the normal is greater than the angle between the refracted Ray and the normal. It bends towards the normal If if light travels from a denser medium to a less dense medium! (eg from glass to sit), then the speed of the wave increases and the angle of incidence is smaller than the angle of Refraction. It bends away from the normal.

like 0 dislike 0 February 23, 2010 at 11:57 PM Comparision: Both reflection and refractions is phenomenon related with wavemotion of sound, electromagnetic waves icluding light. 1a The sound or light or wave bounce back in reflection. The incident ray ,and the point of incidence, the normal drawn at the point of incidence and the relected ray reflected ray are all in the same plane. 1b. In refraction also the incident ray, the point of incidence, the normal drawn at the point of incidence and the refracted ray are all in the same olane. Contrast: 2a.In reflection, the angle of incidenct ray with the normal = angle of reflected ray with the normal 2b. In refraction, the angle i, of incidence with the normal and the angle r of refracted ray are different and they obey Snell's law. sin i / sin r = velocity of incidence/ velocity of refraction = 3a In reflection the image gets the lateral inversion 3b In refraction the image gets change in vertical plane or inversion etc.

like 0 dislike 0 Polarization Light Waves and Color - Lesson 1 - How Do We Know Light is a Wave? Polarization Thin Film Interference Polarization A light wave is an electromagnetic wave that travels through the vacuum of outer space. Light waves are produced by vibrating electric charges. The nature of such electromagnetic waves is beyond the scope of The Physics Classroom Tutorial . For our purposes, it is sufficient to merely say that an electromagnetic wave is a transverse wave that has both an electric and a magnetic component. The transverse nature of an electromagnetic wave is quite different from any other type of wave that has been discussed in The Physics Classroom Tutorial . Let's suppose that we use the customary slinky to model the behavior of an electromagnetic wave. As an electromagnetic wave traveled towards you, then you would observe the vibrations of the slinky occurring in more than one plane of vibration. This is quite different than what you might notice if you were to look along a slinky and observe a slinky wave traveling towards you. Indeed, the coils of the slinky would be vibrating back and forth as the slinky approached; yet these vibrations would occur in a single plane of space.

That is, the coils of the slinky might vibrate up and down or left and right. Yet regardless of their direction of vibration, they would be moving along the same linear direction as you sighted along the slinky. If a slinky wave were an electromagnetic wave, then the vibrations of the slinky would occur in multiple planes. Unlike a usual slinky wave, the electric and magnetic vibrations of an electromagnetic wave occur in numerous planes. A light wave that is vibrating in more than one plane is referred to as unpolarized light. Light emitted by the sun, by a lamp in the classroom, or by a candle flame is unpolarized light. Such light waves are created by electric charges that vibrate in a variety of directions, thus creating an electromagnetic wave that vibrates in a variety of directions. This concept of unpolarized light is rather difficult to visualize. In general, it is helpful to picture unpolarized light as a wave that has an average of half its vibrations in a horizontal plane and half of its vibrations in a vertical plane. It is possible to transform unpolarized light into polarized light. Polarized light waves are light waves in which the vibrations occur in a single plane.

The process of transforming unpolarized light into polarized light is known as polarization. There are a variety of methods of polarizing light. The four methods discussed on this page are: Polarization by Use of a Polaroid Filter The most common method of polarization involves the use of a Polaroid filter. Polaroid filters are made of a special material that is capable of blocking one of the two planes of vibration of an electromagnetic wave. (Remember, the notion of two planes or directions of vibration is merely a simplification that helps us to visualize the wavelike nature of the electromagnetic wave.) In this sense, a Polaroid serves as a device that filters out one-half of the vibrations upon transmission of the light through the filter. When unpolarized light is transmitted through a Polaroid filter, it emerges with one-half the intensity and with vibrations in a single plane; it emerges as polarized light. A Polaroid filter is able to polarize light because of the chemical composition of the filter material. The filter can be thought of as having long-chain molecules that are aligned within the filter in the same direction.

During the fabrication of the filter, the long-chain molecules are stretched across the filter so that each molecule is (as much as possible) aligned in say the vertical direction. As unpolarized light strikes the filter, the portion of the waves vibrating in the vertical direction are absorbed by the filter. The general rule is that the electromagnetic vibrations that are in a direction parallel to the alignment of the molecules are absorbed. The alignment of these molecules gives the filter a polarization axis. This polarization axis extends across the length of the filter and only allows vibrations of the electromagnetic wave that are parallel to the axis to pass through. Any vibrations that are perpendicular to the polarization axis are blocked by the filter. Thus, a Polaroid filter with its long-chain molecules aligned horizontally will have a polarization axis aligned vertically. Such a filter will block all horizontal vibrations and allow the vertical vibrations to be transmitted (see diagram above). On the other hand, a Polaroid filter with its long-chain molecules aligned vertically will have a polarization axis aligned horizontally; this filter will block all vertical vibrations and allow the horizontal vibrations to be transmitted. Polarization of light by use of a Polaroid filter is often demonstrated in a Physics class through a variety of demonstrations. Filters are used to look through and view objects.

The filter does not distort the shape or dimensions of the object; it merely serves to produce a dimmer image of the object since one-half of the light is blocked as it passed through the filter. A pair of filters is often placed back to back in order to view objects looking through two filters. By slowly rotating the second filter, an orientation can be found in which all the light from an object is blocked and the object can no longer be seen when viewed through two filters. What happened? In this demonstration, the light was polarized upon passage through the first filter; perhaps only vertical vibrations were able to pass through. These vertical vibrations were then blocked by the second filter since its polarization filter is aligned in a horizontal direction. While you are unable to see the axes on the filter, you will know when the axes are aligned perpendicular to each other because with this orientation, all light is blocked. So by use of two filters, one can completely block all of the light that is incident upon the set; this will only occur if the polarization axes are rotated such that they are perpendicular to each other. A picket-fence analogy is often used to explain how this dual-filter demonstration works.

A picket fence can act as a polarizer by transforming an unpolarized wave in a rope into a wave that vibrates in a single plane. The spaces between the pickets of the fence will allow vibrations that are parallel to the spacings to pass through while blocking any vibrations that are perpendicular to the spacings. Obviously, a vertical vibration would not have the room to make it through a horizontal spacing. If two picket fences are oriented such that the pickets are both aligned vertically, then vertical vibrations will pass through both fences. On the other hand, if the pickets of the second fence are aligned horizontally, then the vertical vibrations that pass through the first fence will be blocked by the second fence. This is depicted in the diagram below. In the same manner, two Polaroid filters oriented with their polarization axes perpendicular to each other will block all the light. Now that's a pretty cool observation that could never be explained by a particle view of light. Polarization by Reflection Unpolarized light can also undergo polarization by reflection off of nonmetallic surfaces. The extent to which polarization occurs is dependent upon the angle at which the light approaches the surface and upon the material that the surface is made of.

Metallic surfaces reflect light with a variety of vibrational directions; such reflected light is unpolarized. However, nonmetallic surfaces such as asphalt roadways, snowfields and water reflect light such that there is a large concentration of vibrations in a plane parallel to the reflecting surface. A person viewing objects by means of light reflected off of nonmetallic surfaces will often perceive a glare if the extent of polarization is large. Fishermen are familiar with this glare since it prevents them from seeing fish that lie below the water. Light reflected off a lake is partially polarized in a direction parallel to the water's surface. Fishermen know that the use of glare-reducing sunglasses with the proper polarization axis allows for the blocking of this partially polarized light. By blocking the plane-polarized light, the glare is reduced and the fisherman can more easily see fish located under the water. Polarization by Refraction Polarization can also occur by the refraction of light. Refraction occurs when a beam of light passes from one material into another material. At the surface of the two materials, the path of the beam changes its direction. The refracted beam acquires some degree of polarization. Most often, the polarization occurs in a plane perpendicular to the surface.

The polarization of refracted light is often demonstrated in a Physics class using a unique crystal that serves as a double-refracting crystal. Iceland Spar, a rather rare form of the mineral calcite, refracts incident light into two different paths. The light is split into two beams upon entering the crystal. Subsequently, if an object is viewed by looking through an Iceland Spar crystal, two images will be seen. The two images are the result of the double refraction of light. Both refracted light beams are polarized - one in a direction parallel to the surface and the other in a direction perpendicular to the surface. Since these two refracted rays are polarized with a perpendicular orientation, a polarizing filter can be used to completely block one of the images. If the polarization axis of the filter is aligned perpendicular to the plane of polarized light, the light is completely blocked by the filter; meanwhile the second image is as bright as can be. And if the filter is then turned 90-degrees in either direction, the second image reappears and the first image disappears. Now that's pretty neat observation that could never be observed if light did not exhibit any wavelike behavior. Watch It!

In the demonstration below, the word PHUN (as in Physics is ...) is written on the glass panel of a classroom-style overhead projector. A sample of Iceland spar is placed over the word PHUN. Two images of the word PHUN can be faintly seen in the early seconds of the movie. The crystal double refracts light that passes through it. At about the 8-second mark, a Polaroid filter is placed over the crystal and rotated. As it rotates, the two images alternately fade in and out. The light passing through the crystal becomes polarized and when the Polaroid filter is rotated, it blocks and transmits the two light paths in alternating fashion. The result is that the two images of PHUN can be seen one at a time. Pretty cool stuff! Polarization by Scattering Polarization also occurs when light is scattered while traveling through a medium. When light strikes the atoms of a material, it will often set the electrons of those atoms into vibration. The vibrating electrons then produce their own electromagnetic wave that is radiated outward in all directions. This newly generated wave strikes neighboring atoms, forcing their electrons into vibrations at the same original frequency. These vibrating electrons produce another electromagnetic wave that is once more radiated outward in all directions.

This absorption and reemission of light waves causes the light to be scattered about the medium. (This process of scattering contributes to the blueness of our skies, a topic to be discussed later .) This scattered light is partially polarized. Polarization by scattering is observed as light passes through our atmosphere. The scattered light often produces a glare in the skies. Photographers know that this partial polarization of scattered light leads to photographs characterized by a washed-out sky. The problem can easily be corrected by the use of a Polaroid filter. As the filter is rotated, the partially polarized light is blocked and the glare is reduced. The photographic secret of capturing a vivid blue sky as the backdrop of a beautiful foreground lies in the physics of polarization and Polaroid filters. Applications of Polarization Polarization has a wealth of other applications besides their use in glare-reducing sunglasses. In industry, Polaroid filters are used to perform stress analysis tests on transparent plastics. As light passes through a plastic, each color of visible light is polarized with its own orientation. If such a plastic is placed between two polarizing plates, a colorful pattern is revealed. As the top plate is turned, the color pattern changes as new colors become blocked and the formerly blocked colors are transmitted.

A common Physics demonstration involves placing a plastic protractor between two Polaroid plates and placing them on top of an overhead projector. It is known that structural stress in plastic is signified at locations where there is a large concentration of colored bands. This location of stress is usually the location where structural failure will most likely occur. Perhaps you wish that a more careful stress analysis were performed on the plastic case of the CD that you recently purchased. Polarization is also used in the entertainment industry to produce and show 3-D movies. Three-dimensional movies are actually two movies being shown at the same time through two projectors. The two movies are filmed from two slightly different camera locations. Each individual movie is then projected from different sides of the audience onto a metal screen. The movies are projected through a polarizing filter. The polarizing filter used for the projector on the left may have its polarization axis aligned horizontally while the polarizing filter used for the projector on the right would have its polarization axis aligned vertically. Consequently, there are two slightly different movies being projected onto a screen. Each movie is cast by light that is polarized with an orientation perpendicular to the other movie. The audience then wears glasses that have two Polaroid filters.

Each filter has a different polarization axis - one is horizontal and the other is vertical. The result of this arrangement of projectors and filters is that the left eye sees the movie that is projected from the right projector while the right eye sees the movie that is projected from the left projector. This gives the viewer a perception of depth. Our model of the polarization of light provides some substantial support for the wavelike nature of light. It would be extremely difficult to explain polarization phenomenon using a particle view of light. Polarization would only occur with a transverse wave. For this reason, polarization is one more reason why scientists believe that light exhibits wavelike behavior. Watch It! The pattern of a hot air balloon was sketched onto a glass plate. Cellophane tape was then added to the pattern such that each "sector" of the balloon consisted of tape alligned in a distinctly different direction than adjacent "sectors". A hobby knife was used to carefully remove overlap of tape from one sector into adjoining sectors. The cellophane tape is able to rotate the axis of polarization of the wavelengths (i.e., color) of polarized light different amounts.

In the demonstration, a polaroid filter is placed upon the glass panel of a classroom style overhead projector. Light passing through the filter becomes polarized. Different sectors of the taped glass will rotate the axes of polarization of the different wavelengths of light different amounts. A second filter is then placed over the taped glass. This second filter permits passage of wavelengths (i.e. colors) of light whose axis of polarization line up with the transmitting axis of the filter; other wavelengths are blocked. Thus, different sectors appear different colors when viewed through both filters. Refrection of light | definition of Refrection of light by Medical dictionary Refrection of light | definition of Refrection of light by Medical dictionary Related to Refrection of light: Refraction of Light , Dispersion of light refraction [re-frak´shun] the act or process of refracting; specifically, the determination of the refractive errors of the eye and their correction with glasses. the deviation of light in passing obliquely from one medium to another of different density. cycloplegic refraction a type of static refraction , measured after lens accommodation is paralyzed by administration of cycloplegic eye drops. double refraction refraction in which incident rays are divided into two refracted rays.

dynamic refraction refraction of the eye during accommodation. ocular refraction the refraction of light produced by the media of the normal eye and resulting in the focusing of images upon the retina. static refraction refraction of the eye when its accommodation is paralyzed. re·frac·tion (rē-frak'shŭn), 1. The deflection of a ray of light when it passes from one medium into another of different optic density; in passing from a denser into a rarer medium it is deflected away from a line perpendicular to the surface of the refracting medium; in passing from a rarer to a denser medium it is bent toward this perpendicular line. 2. The act of determining the nature and degree of the refractive errors in the eye and correction of the same by lenses. refraction /re·frac·tion/ (re-frak´shun) 1. the act or process of refracting; specifically, the determination of the refractive errors of the eye and their correction with lenses. Refraction by the eye in (A) emmetropia; (B) hyperopia; and (C) myopia. 2.

the deviation of light in passing obliquely from one medium to another of different density.refrac´tive double refraction refraction in which incident rays are divided into two refracted rays, so as to produce a double image. dynamic refraction the normal accommodation of the eye which is continually exerted without conscious effort. refraction (rĭ-frăk′shən) n. 1. The deflection of a wave, such as a light or sound wave, when it passes obliquely from one medium into another having a different index of refraction. 2. Medicine a. The ability of the eye to bend light so that an image is focused on the retina. b. Determination of this ability in an eye. re·frac′tion·al, re·frac′tive adj. re·frac′tive·ly adv. re·frac′tive·ness, re′frac·tiv′i·ty (rē′frăk-tĭv′ĭ-tē) n.

refraction [rifrak′shən] Etymology: L, refringere, to break apart 1 n, the change of direction of energy as it passes from one medium to another of different density. 2 n, an examination to determine and correct refractive errors of the eye. 3 n, (in ultrasonography) the phenomenon of bending wave fronts as the acoustic energy propagates from the medium of one acoustic velocity to a second medium of differing acoustic velocity. 4 adj, pertaining to the recovery period after an action potential either in muscular or nervous tissue. refractive, adj. refraction Ophthalmology The determination of the optical state of the eye and the basis for prescribing glasses and contact lenses. Optics The alteration of a light wave when it passes from one medium to another—e.g., from a lens to water. re·frac·tion (rē-frak'shŭn) 1.

The deflection of a ray of light when it passes from one medium into another of different optic density; in passing from a denser into a rarer medium, it is deflected away from a line perpendicular to the surface of the refracting medium; in passing from a rarer to a denser medium, it is bent toward this perpendicular line. 2. The act of determining the nature and degree of the refractive errors in the eye and correction of them by lenses. Synonym(s): refringence . refraction 1. The bending of light rays that occurs when they pass obliquely from a transparent medium of one density to one of another density. 2. The assessment of the optical errors of the eyes so that appropriate correcting spectacles can be prescribed. Refraction The bending of light rays as they pass from one medium through another. Used to describe the action of the cornea and lens on light rays as they enter they eye. Also used to describe the determination and measurement of the eye's focusing system by an optometrist or ophthalmologist. ; refringence radiation divergence as it passes between media of different densities or across an interface refraction 1.

The change in direction of the path of light as it passes obliquely from one medium to another having a different index of refraction (Fig. R7). 2. The process of measuring and correcting the refractive error of the eyes. Syn. refraction of the eye; sight testing (obsolete term). angle of refraction See angle of refraction . binocular refraction A clinical procedure in which the subjective measurement of refraction of each eye is performed while both eyes are viewing a test. The visual examination is thus carried out under more natural conditions than when one eye is closed; the sizes of the pupils are similar and the accommodation-convergence relationship is maintained. There are various such methods; using polarized targets (e.g. Vectograph slides; Parallel-testing Infinity Balance test), using a septum (e.g. Turville Infinity Balance test), or fogging (e.g. Humphriss Immediate Contrast test). These methods give better results than refracting monocularly, especially in latent hyperopia, hyperopic anisometropia, pseudomyopia, cyclophoria, etc. and no additional step for binocular balancing is necessary. See Humphriss method; balancing test; infinity balance Turville test; testing in parallel .

cycloplegic refraction Assessment of the refract-ive state of the eye when accommodation has been totally or partially paralysed by a cycloplegic (e.g. cyclopentolate 1% eyedrops, or atropine 0.5 or 1% ointment). This may be carried out in children to reveal the full extent of a hyperopia or in the initial assessment of accommodative esotropia, but only occasionally in adults as fogging methods usually suffice for them. See cycloplegia ; accommodative strabismus . double refraction The splitting of an incident ray into two (ordinary and extraordinary) by a birefringent medium. See anisotropic ; birefringence ; Nicol prism ; Wollaston prism . dynamic refraction Determination of the refract-ive state of the eye when accommodation is stimulated, as distinguished from static refraction which is the determination of the refractive state of the eye when accommodation is at rest or paralysed. See refractive error ; dynamic retinoscopy . error of refraction See ametropia ; refractive error . refraction of the eye 1. See refraction. 2.

Refraction of light by the optical media of the eye. index of refraction See index of refraction . laser refraction A method of subjective refraction in which the patient observes a slowly rotating drum, on the surface of which is perceived a speckle pattern resulting from illumination by a laser. The speckle pattern appears to move only when the eye is not focused for the fixation distance. If the perceived movement of the pattern is opposite to that of the drum, the eye is myopic and if the perceived movement of the pattern is in the same direction as the drum, the eye is hyperopic. Correction can be determined by placing a lens in front of the eye, which will neutralize the movement; at that point the eye is focused for the fixation distance. Astigmatism can be measured by rotating the drum in various meridians. The drum can be placed at infinity or at near (an allowance for the radius of curvature of the drum and the distance must then be made). This method can be useful for mass screening, especially children, as accommodation is not stimulated as much as with Snellen letters. It has been very useful as a research tool for accommodation studies where it is arranged as part of a Badal optometer.

manifest refraction The refractive error or the process of determining it, when accommodation is at rest (but not paralysed). See cycloplegic refraction . objective refraction Measurement of the refraction of the eye that is not based on the patient's judgements, as when using an objective optometer or a retinoscope. See photorefraction . static refraction See dynamic refraction ; refract-ive error. subjective refraction Measurement of the refraction of the eye based on the patient's judgements. See fogging method; optometer ; duochrome test; fan and block test; plus 1.00 D blur test. Fig. R7 Refraction of light from water into air. Object O forms an image at O′ which appears closer to the surface than it actually is.

Thus the apparent thickness t′ of a pool of water (or block of glass), in air, is smaller than its true thickness t and the greater the index of refraction n, the smaller it appears, i.e Apparent depth | definition of Apparent depth by Medical dictionary Apparent depth | definition of Apparent depth by Medical dictionary refraction [re-frak´shun] the act or process of refracting; specifically, the determination of the refractive errors of the eye and their correction with glasses. the deviation of light in passing obliquely from one medium to another of different density. cycloplegic refraction a type of static refraction , measured after lens accommodation is paralyzed by administration of cycloplegic eye drops. double refraction refraction in which incident rays are divided into two refracted rays. dynamic refraction refraction of the eye during accommodation. ocular refraction the refraction of light produced by the media of the normal eye and resulting in the focusing of images upon the retina. static refraction refraction of the eye when its accommodation is paralyzed. re·frac·tion (rē-frak'shŭn), 1.

The deflection of a ray of light when it passes from one medium into another of different optic density; in passing from a denser into a rarer medium it is deflected away from a line perpendicular to the surface of the refracting medium; in passing from a rarer to a denser medium it is bent toward this perpendicular line. 2. The act of determining the nature and degree of the refractive errors in the eye and correction of the same by lenses. refraction /re·frac·tion/ (re-frak´shun) 1. the act or process of refracting; specifically, the determination of the refractive errors of the eye and their correction with lenses. Refraction by the eye in (A) emmetropia; (B) hyperopia; and (C) myopia. 2. the deviation of light in passing obliquely from one medium to another of different density.refrac´tive double refraction refraction in which incident rays are divided into two refracted rays, so as to produce a double image. dynamic refraction the normal accommodation of the eye which is continually exerted without conscious effort. refraction (rĭ-frăk′shən) n. 1.

The deflection of a wave, such as a light or sound wave, when it passes obliquely from one medium into another having a different index of refraction. 2. Medicine a. The ability of the eye to bend light so that an image is focused on the retina. b. Determination of this ability in an eye. re·frac′tion·al, re·frac′tive adj. re·frac′tive·ly adv. re·frac′tive·ness, re′frac·tiv′i·ty (rē′frăk-tĭv′ĭ-tē) n. refraction [rifrak′shən] Etymology: L, refringere, to break apart 1 n, the change of direction of energy as it passes from one medium to another of different density. 2 n, an examination to determine and correct refractive errors of the eye. 3 n, (in ultrasonography) the phenomenon of bending wave fronts as the acoustic energy propagates from the medium of one acoustic velocity to a second medium of differing acoustic velocity. 4 adj, pertaining to the recovery period after an action potential either in muscular or nervous tissue. refractive, adj.

refraction Ophthalmology The determination of the optical state of the eye and the basis for prescribing glasses and contact lenses. Optics The alteration of a light wave when it passes from one medium to another—e.g., from a lens to water. re·frac·tion (rē-frak'shŭn) 1. The deflection of a ray of light when it passes from one medium into another of different optic density; in passing from a denser into a rarer medium, it is deflected away from a line perpendicular to the surface of the refracting medium; in passing from a rarer to a denser medium, it is bent toward this perpendicular line. 2. The act of determining the nature and degree of the refractive errors in the eye and correction of them by lenses. Synonym(s): refringence . refraction 1. The bending of light rays that occurs when they pass obliquely from a transparent medium of one density to one of another density. 2. The assessment of the optical errors of the eyes so that appropriate correcting spectacles can be prescribed. Refraction The bending of light rays as they pass from one medium through another.

Used to describe the action of the cornea and lens on light rays as they enter they eye. Also used to describe the determination and measurement of the eye's focusing system by an optometrist or ophthalmologist. ; refringence radiation divergence as it passes between media of different densities or across an interface refraction 1. The change in direction of the path of light as it passes obliquely from one medium to another having a different index of refraction (Fig. R7). 2. The process of measuring and correcting the refractive error of the eyes. Syn. refraction of the eye; sight testing (obsolete term). angle of refraction See angle of refraction . binocular refraction A clinical procedure in which the subjective measurement of refraction of each eye is performed while both eyes are viewing a test. The visual examination is thus carried out under more natural conditions than when one eye is closed; the sizes of the pupils are similar and the accommodation-convergence relationship is maintained. There are various such methods; using polarized targets (e.g. Vectograph slides; Parallel-testing Infinity Balance test), using a septum (e.g. Turville Infinity Balance test), or fogging (e.g. Humphriss Immediate Contrast test).

These methods give better results than refracting monocularly, especially in latent hyperopia, hyperopic anisometropia, pseudomyopia, cyclophoria, etc. and no additional step for binocular balancing is necessary. See Humphriss method; balancing test; infinity balance Turville test; testing in parallel . cycloplegic refraction Assessment of the refract-ive state of the eye when accommodation has been totally or partially paralysed by a cycloplegic (e.g. cyclopentolate 1% eyedrops, or atropine 0.5 or 1% ointment). This may be carried out in children to reveal the full extent of a hyperopia or in the initial assessment of accommodative esotropia, but only occasionally in adults as fogging methods usually suffice for them. See cycloplegia ; accommodative strabismus . double refraction The splitting of an incident ray into two (ordinary and extraordinary) by a birefringent medium. See anisotropic ; birefringence ; Nicol prism ; Wollaston prism .

dynamic refraction Determination of the refract-ive state of the eye when accommodation is stimulated, as distinguished from static refraction which is the determination of the refractive state of the eye when accommodation is at rest or paralysed. See refractive error ; dynamic retinoscopy . error of refraction See ametropia ; refractive error . refraction of the eye 1. See refraction. 2. Refraction of light by the optical media of the eye. index of refraction See index of refraction . laser refraction A method of subjective refraction in which the patient observes a slowly rotating drum, on the surface of which is perceived a speckle pattern resulting from illumination by a laser. The speckle pattern appears to move only when the eye is not focused for the fixation distance. If the perceived movement of the pattern is opposite to that of the drum, the eye is myopic and if the perceived movement of the pattern is in the same direction as the drum, the eye is hyperopic. Correction can be determined by placing a lens in front of the eye, which will neutralize the movement; at that point the eye is focused for the fixation distance.

Astigmatism can be measured by rotating the drum in various meridians. The drum can be placed at infinity or at near (an allowance for the radius of curvature of the drum and the distance must then be made). This method can be useful for mass screening, especially children, as accommodation is not stimulated as much as with Snellen letters. It has been very useful as a research tool for accommodation studies where it is arranged as part of a Badal optometer. manifest refraction The refractive error or the process of determining it, when accommodation is at rest (but not paralysed). See cycloplegic refraction . objective refraction Measurement of the refraction of the eye that is not based on the patient's judgements, as when using an objective optometer or a retinoscope. See photorefraction . static refraction See dynamic refraction ; refract-ive error. subjective refraction Measurement of the refraction of the eye based on the patient's judgements. See fogging method; optometer ; duochrome test; fan and block test; plus 1.00 D blur test. Fig. R7 Refraction of light from water into air.

Object O forms an image at O′ which appears closer to the surface than it actually is. Thus the apparent thickness t′ of a pool of water (or block of glass), in air, is smaller than its true thickness t and the greater the index of refraction n, the smaller it appears, i.e

Question: What is the name for the change of direction when a ray of light passes from one medium (e.g. water) to another (e.g. air)?
Answer: Refraction