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Reflection of Light

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Leigh Ellis

on 22 April 2011

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Transcript of Reflection of Light

Reflection of Light Light traveling though a uniform substance, such as air, water, or a vacuum, always travels in a straight line. When light encounters a a differant substance, its path will change. If a material is opaque to the light, such as the dark, highly polished surface of a wooden table, the light will not pass into the table more than a few wave lengths. Part of the light is absorbed, and the rest is deflected at the surface. Mirrors Flat Mirrors There are 4 different types of mirrors. Flat Curved Convex Sperical Parabolic The manner in which light is reflected from a surface depends on the surface's smoothness. Light that is redlected from a rough textured surface, such as paper, cloth, or unpolished wood, is reflectedin many different directions Light reflected from smooth, shiny surfaces, such as a mirror or water in a pond, is reflected on one direction only. This type of reflection is called specular reflection. A surface is considered smooth if its surface cariations are small compared with the wavelength of the incoming light. The simplest mirror is the Flat mirror. If an object, such as a pencil, is placed at a distance in front of a flat mirror, light is bouned off pencil, light rays will spread out from the pencil and and reflect from the mirrors surface. When incoming rays of light strike a smooth reflecting surface at an angle close to the surface, the reflected rays are also close to the surface. When the incoming rays are high above the reflecting surface, the reflected rays are also high above the the surface. Curved Mirrors Concave Spherical Small, circular mirrors such as those used on dressing tables, may appear to be flat mirrors at a glance. However, objects that are close to the mirror appear larger than the object. Objects far from the mirror appear smaller and upside down. A sperical mirror with light reflecting from its silvered, concave surface is called a concave spherical mirror. As the name implies, this mirror has a the shape of part of a sphere's surface. This mirror is used whenever a magnified image of an object is needed. A light bulb is placed upright at a distance from the concave sperical mirror. The base of the bulb is along the mirrors principal axis, which is the line that extends infanantly from the center of the mirrors surface throught the center of curvature. Light rays diverge from the light bulb, reflect from the mirrors surface, and converge at some distance in front of the mirror. Becasue the light rays reflected by the mirror actually pass through the image point which in this case is below the principal axis, the image is in front of the mirror. If you place a piece of paper at the image point, you will see on the paper a sharp and clear image of the light bulb. As you move the paper in either directoin away from the image point, the rays diverge, and the image becomes unfocused. An image of this tyoe is called a real image. This is the way that movies are displayed in a screen when you go to the movies or watch them on a projector. Convex Spherical Mirrors whose reflecting surface is an outward-curved segment of a sphere. Images in this mirrorare distorted near the mirrors edges, and the image is smaller than the object. This mirror is also called a diverging mirror because the incoming rays diverge after reflection as though they were coming from some point beyond the mirror. The resulting image is is therefore always virtual and the image distance is negative. Convex Sperical mirrors take the objects in a large field of view and produce a small image so they are well suited for providing a fixed observer with a complete view of a large area. These mirrors are often placedin stores to help employees monitor customers and at the intersections of busy hallways so that people in both hallways can tell when others are approaching. The side biew mirror on the passenger's side of a car is another example of a convex spherical mirror. This mirror usually carries the warning, "objects are closer than they appear." Without this warningm a driver might think that he or she is looking into a flat mirror, which does not alter the size of the image. The driver could therefore think that the vehicle is farther away than it really is because the image is smaller. Parabolic Mirror When light rays from an object are near the principal axis, all of the reflected rays pass through the image point. Rays that reflect at points on the mirror far from the principal axis converage at slightly different points on the axis. This produces a blurred image. This affect is called Spherical Aberration. Parabolic mirrors are segments of a paraboloid ( a three-dimensional porabola) whose inner surface is reflecting. All rays parrallel to the principal axis converge at the focal point regardless of where on the mirror's surface the rays reflect. Parabolic reflectors are ideal for flashlights and automobile headlights. These reflectors are exclusively used because they are reasier to manufacture than parabolic mirrors and are less expensive. Reflecting tetescopes also use parabolic mirrors, but not all telescopes use visible light. Because all electromagnetic radiation obeys the law of reflection, parabolic surfaces can be constructed to reflect and focus electromagnetis radiation of different wavelengths. A radio telescope consists of a large metal parabolic surface that reflets radio waves in order to revieve radio signals from objects in space. There are 2 types of telescopes that use visible light. The Refracting Telescope uses a combination of lenses to form an image. The other type uses a curved mirror and small lense to form an image. This type is called a Reflecting Telescope.
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