He Angles, She Refracts

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Other deaths are present for me, as well, in their particulars,. Do I think everything has memory in the form of energy, so nothing. I wish I could hold that thought. My tongue tingles now with magnesium-depleted nerve shocks, a mouthful of shards so small they would look lovely and undangerous if I could spit them into my palm and show you, like the memory of broken glass I saw on a night street from my childhood in Jersey City, and said, [End Page ].

Mama, these must be fallen stars. Her hand was warm around mine, and we walked in unison, her pace slowing, so briefly we were one four-legged animal staring at the littered ground with dual wonder. That might be where it began for me, this searching for the god of science, a way to bear the beauty of what I would come to love.

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One of her poems was selected by Sherman Alexie for inclusion in The Best American Poetry , and she has edited two anthologies. The light travels down the fibre only making glancing collisions with the walls so that total internal reflection occurs. Fibre-optic cabling is becoming more important in telecommunications roll-out of the NBN and in medicine clear pictures of inside the body can be taken. Sound waves propagating through air are bent and undergo refraction when the air temperature varies the higher the temperature, the greater the speed of sound.

On a warm day, the air near the ground may be appreciably warmer than the rest of the air, so the speed of sound near the ground is greater. The sound will be refracted and bent away from the ground resulting in sound that does not seem to travel as far.

Refraction and Lenses: Problem Set

Medicine To determine the refraction of (an eye, for example). . Iowa, the new material makes it possible to refract visible light to the left, or at a negative angle. Refraction and the Ray Model of Light - Lesson 1 - Refraction at a Boundary As you look at Mary in class, you are able to see Mary because she is illuminated . knows that the amount of refraction that occurs is dependent upon the angle at.

At night, the ground is cold and the speed of sound is less than the speed further above the ground, resulting in the sound being bent towards the ground. Sounds can be heard over considerably longer distances. Refraction of sound waves. Sound waves are bend in air.

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We hear thunder when the lightning is close to us, but we often do not hear the thunder for distant lightning because of refraction — sounds travel slower at higher altitudes and bends away from the ground, so that we may not hear the thunder clap. Refraction leads to a bending of the wavefronts when entering a new medium where the speed of the wave is different. To see why more clearly, we can consider a solder analogy as shown in figure 7. The solders are marching from firm ground medium 1 into a muddy region medium 2.

The solders that reach the mud first are slowed down first and the row of solders bend. Look at figure 6 again — in warmer air, part of the wavefront moves faster than in colder air, so the bending of the wavefront is either away or towards the ground. The multiple reflections and refractions of ultrasonic waves are used by doctors for generating images inside our bodies. When high frequency short wavelength ultrasound enters the body, it reflects more strongly from the outside of an organ than from its interior, and an image of the organ is obtained.

Image of a fetus using short wavelength ultrasonic waves. Predict how the relative intensity of the reflected and refracted waves change as the parameters are changed. Think about a golf ball or a stone skipping across the surface of water. List of refractive indices. The point of the question is to point out the myriad of situations in which the Law of Reflection holds.

Two famous British scientists, Isaac Newton and Robert Hooke, debated the nature of light in the s. Newton claimed light was composed of tiny "corpuscles", or particles. Hooke claimed light was a continuous wave. Think about the behavior of light when it is reflected by a by a smooth surface, and b by a rough surface.

In each case, is the behavior of light more like particles, more like a wave, or explained equally well by either theory? Newton's theory of light is nicely explained in the book Einstein and Bohr found in the References page. Students are not expected to have familiarity with the arguments, but hopefully they will recognize that both particles and waves obey the law of reflection from both smooth and rough surfaces.

We see objects when light reflected by them reaches our eyes.

Ray Optics: Refraction and Lenses

Do you think this reflection by most objects is total reflection or diffuse reflection? Since most objects are visible from all directions, light is scattered by them in all directions. Thus the reflection is diffuse. Laser light is generally not visible as it travels through air. If you have access to a laser or to a laser pointer, verify this for yourself. Yet if you shine a laser through chalk dust, the beam is visible.

How to calculate the angle of refraction of a ray inside a glass block

Explain why this occurs. Chalk dust provides multiple surfaces from which the laser beam can reflect. Since the laser beam will strike dust particles at a wide range of incident angles, the light will be diffusely reflected and thus visible from a variety of angles. Without the dust, no reflection occurs, so no laser light reaches the observer. If a laser beam is sent across a classroom, only students in the direct line of the beam would be able to see that the laser is shining. But if the beam strikes a wall, the entire class will be able to see the spot made by the beam on the wall.

Laser light is by definition well-columnated, so it will not be emitted toward students other than those in the direct path of the beam. The wall, however, scatters the light in all directions due to diffuse reflection. An apparently smooth wall looks very bumpy to a laser beam. The reflected light is thus visible to the entire class as a spot on the wall. A scientist looking into a flat mirror hung perfectly perpendicular to the floor cannot see her feet but can only see down to the hem of her labcoat. Will she be able to see her feet if she backs away from the mirror?

What if she moves toward the mirror? A drawing of light rays may help you explain your answer. This one will be tricky for students who have not studied ray diagrams in more detail than this material provides.

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The scientist's view is limited by what light can reflect off the bottom of the mirror and reach her eye as constrained by the law of reflection. In this problem, the bottom of the mirror is located halfway between the labcoat hem and the eye. In the ray diagram to the left below, the red light ray from the hem of the coat is reflected by the mirror into the scientist's eye.

The blue light ray from her shoe, however, is reflected above her head. As the scientist moves back, the mirror will continue to be vertically located halfway between the hem and the eye, and both the eye and the hem will continue to be equal distances from the mirror. Thus the angle of light incident on the mirror from the hem and the angle of reflection by the mirror to the eye will change together.

The scientist will not be able to see any more of herself as she backs up. The ray diagram on the right below shows that the ray from the hem still reaches the eye but the ray from the shoe still reflects over her head. Due to the difficulties in drawing accurate ray diagrams for two-dimensional images, students might claim that the diagram on the right shows more of the scientist's image in the mirror.

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But one must carefully draw the light rays from each point on the image to get an accurate picture. Such treatment should show that no more and no less of the scientist is imaged as she moves back from the mirror. A stream of tennis balls striking a metal plate will exhibit total reflection, while the same stream of tennis balls reflecting off of an old, cracked sidewalk will exhibit diffuse reflection. What characteristic s of a surface distinguish es whether tennis balls exhibit diffuse or total reflection when striking that surface? If the irregularities in a surface are close to the same size as the tennis ball greater than a few percent of the part of the ball in contact with the surface , they can influence the average force on the ball and so visibly affect the direction it travels.

Smaller bumps will have a less significant effect overall. The cracks in the sidewalk are big compared with tennis balls, so whether or not a ball lands on the crack makes a big difference in its final trajectory. The irregularities in a metal plate are generally much tinier than a tennis ball, so the balls will all see the surface as smooth.

Snell's law

A stream of tennis balls striking a concrete wall will exhibit total reflection while a laser beam of light striking the same wall will be scattered in all directions. What characteristic s of an object distinguish es whether that object exhibits diffuse or total reflection when striking a given surface? This is similar to the previous question. Since the tennis balls are so much bigger than the irregularities in a concrete wall, each tennis ball will have approximately the same angle of incidence when averaged over the portion of the ball in contact with the wall.

Light, on the other hand, interacts at a much smaller scale. The wavelength of light provides a general scale for interactions, and the irregularities in a concrete wall are generally much larger than the wavelengths of visible light. Thus the individual interactions of light with the wall will occur at different angles of incidence, leading to diffuse reflection. What angle will the reflected light make with the surface?

Reflection Refraction

What is the angle of reflection? What was the angle of incidence? What are the physical limits on the index of refraction? According to the theory of relativity, information cannot move between two points any faster than c , the speed of light in vacuum.


Yet a shadow can move much faster than c. You shine this super-flashlight at a large white wall 10 m away, then pass your finger in front of the lamp. On the wall, the shadow of your finger also passes through the beam in 0. But the shadow must travel through a distance of 20 meters in that 0.

Expert Answer

With the development of modern optical and electromagnetic theory, the ancient Snell's law was brought into a new stage. The index of the water cladding is 1. It is the dispersion of light by ordinary glass that is responsible for the familiar splitting of light into its component colors by a prism. Given n lines L and a point P L on each line, find the locus of points Q such that the lengths of the line segments QP L satisfy certain conditions. Light can be transmitted along an optical fibre with almost zero energy loss. This means that a person can be diagnosed and treated through a small incision cut. The critical angle is:

If, instead of your finger, a high-speed bullet passes through the light beam, the resulting shadow will move even faster. The speeds of the shadow in the above example are still well below c , but you can extend this analogy to a wall 20 m away where the beam is 40 m in diameter or to a wall 2,, m away. Of course, a flashlight that would have measureable intensity over a wide angle at that distance would blind individuals near it, but one could still imagine the situation.

It is, after all, analagous to a star that radiates uniformly in all directions with an appreciable intensity at exceptionally far distances. A planet or a giant cloud of interstellar dust passing between that star and the observer would cast a shadow, however small, that could move faster than c at the observer's location.