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Chapter 25 -27 Optics Introduction to Geometric and Physical Optics Geometric Optics: Reflection and Refraction Reflection The Law of Reflection Angle of incidence = Angle of reflection qi = qr All angles are measured with respect to the normal. normal Snell’s Law of Refraction n1 sinq1 = n2 sinq2 n: The refractive index nvacuum º 1, nair » 1, nwater » 1.33, nglass » 1.5 n increases with density n1 n2 More on refractive index nmedium cvacuum = cmedium cvacuum = 3 ´ 10 m / s : speed of light in vacuum 8 n is dimensionless If ndiamond = 2.42, find the speed of light in diamond. cvacuum 3 ´ 10 m / s = = = 1.24 ´ 10 8 m / s ndiamond 2.42 8 cdiamond Optical Illusion Physical optics •Geometric optics treats light as particles (or rays) that travels in straight lines. •Physical optics (wave optics) deals with the wave nature of light, such as the spreading of waves (diffraction) and the interference of waves. Adding waves Constructive interference Destructive interference Combining two waves does not always give you a bigger wave! Ripples Young’s Double Slit (1800) Interference around us
