Dr. Jie Zou PHY 1161 1 Chapter 26 Geometric Optics (Lecture I)
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Dr. Jie Zou PHY 1161 1
Chapter 26
Geometric Optics (Lecture I)
Dr. Jie Zou PHY 1161 2
Outline
Reflection of light The law of reflection Specular and diffuse reflection
Refraction of light Index of refraction Snell’s law
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Rays and Wave Fronts Describe light in terms of
“wave fronts” and “rays” Wave fronts: In the case of
a water wave created by a rock dropped into a still pool of water, the wave fronts indicate the crests of water waves.
Rays: The radial motion of the waves is indicated by the outward-pointing arrows, referred to as rays.
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The Law of Reflection Reflection: Light changes
its direction as being reflected onto a new path from for example a mirror or other shiny objects.
Law of Reflection: r = i and the incident ray, the reflected ray, and the normal lie in the same plane.
i = angle of incidence r = angle of reflection
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Specular reflection: the reflection of light from a smooth surface, in which all the reflected light propagates in a single direction.
Diffuse reflection: If the surface is rough, the reflected light is sent out in a variety of directions.
Specular and Diffuse Reflection
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The Refraction of Light Refraction: When a wave
propagates from a medium in which its speed is v1 to another in which its speed is v2v1 , it will, in general, change its direction of motion. This phenomena is called refraction.
Refraction is the bending of wave fronts and change in direction of propagation due to a change in speed.
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sin1v1
sin2v2
Index of Refraction and Snell’s Law
The speed of light in a given medium, v, is determined by the medium’s index of refraction, n. v = c/n For example: Diamond, n =
2.42; Flint glass, n=1.66; Water, n = 1.33; Air, n = 1.000293 (see Table 26-2)
Snell’s Law: n1sin1 = n2sin2
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Example 26-4
A beam of light in air enters (a) water (n = 1.33) or (b) glass (n = 1.50) at an angle of 60.0° relative to the normal. Find the angle of refraction for each case.
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Homework #11
Chapter 26, P. 941-942, Problems: #50, 51, 53, 54 (Physics, Walker, 4th edition).
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