Chapter%2025-1 - COLLEGE PHYSICS Part II Chapter 25 THE...

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Chapter 25: THE REFLECTION OF LIGHT: MIRRORS 1. Wave Fronts and Rays 2. The Reflection of Light 2. The Formation of Images by a Plane Mirror 3. Reflection by Spherical Mirrors 4. The Formation of Images by Spherical Mirrors 5. The Mirror Equation and the Magnification Equation COLLEGE PHYSICS, Part II
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Reflection and Refraction When an incident light beam hits a surface that separates two transparent materials, such as air and glass, the light is being partially reflected and partially transmitted ( refracted ). (There are other effects, such as absorption, scattering, diffraction, but for now we consider only reflection and transmission.) Usually consideration of just one ray is enough. The directions of the incident, reflected, and refracted rays are usually presented by the angles they make with the normal to the surface, as shown in the lower right part of the Figure.
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LAW OF REFLECTION The incident ray, the reflected ray, and the normal to the surface all lie in the same plane, and the angle of incidence equals the angle of reflection. r i θ θ =
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At large distances from the source, the wavefronts become less and less curved. Waves whose wavefronts are flat surfaces are called plane waves . Naturally, the rays of a plane wave are parallel to each other. Wavefront is a surface that is perpendicular to the direction of propagation of the wave, and all rays have the same phase at the wavefront.
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In specular reflection, the reflected rays are parallel to each other. Reflection at a defined angle from a smooth planar surface is called specular reflection . Random reflection from a rough surface is called diffuse reflection .
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The image obtained by reflection is not identical to the object: In the mirror, the sense of right and left is reversed. The person’s right hand becomes the image’s left hand. A right handed helix becomes a left handed helix, etc. Right-handed helix Left-handed helix
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The reflection in a plane (flat) mirror: 1. is upright. 2. is the same size as the object. 3. the image is as far behind the mirror as the object in front of it. A ray of light from the top of the chess piece reflects from the mirror. To the eye, the ray seems to come from behind the mirror. Because none of the rays directly comes from the image, it is called a virtual image . Formation of Images by a Plane Mirror
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The image distance is equal to the object distance. o 1 90 θ β + = o 2 90 α β + = and but α θ = hence 1 2 β β = The triangles ABC and CBD are identical (congruent) . o 1 2 i d htan htan d β β = = = h So, the object and the image are at equal distances from the surface of the mirror.
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