Electromagnetic WavesSo farSlide 3Reflection & RefractionReflectionLight ReflectionPrinciple of Least TimeSlide 8Mirror, Mirror, on the wall, how big do you have to be to see it all? The strange world of images.The speed of lightIndex of RefractionNoticeHuygen’s PrincipleSlide 14Slide 15Slide 16Some GeometrySlide 18Snell’s Law of RefractionAnother View Of Reflection (Huygen’s)Both TogetherSlide 22Slide 23Total Reflection – Optical FiberSlide 25Slide 26dichroismSlide 28Slide 29Slide 30Slide 31MirageSlide 33Part IIElectromagnetic Waves1So far2We have discussedThe nature of EM wavesSome of the properties of EM waves.Now we will discussEM waves and opticsMirrorsLensesApplications3Reflection & Refraction4Reflection5Light Reflection6Angles of incidence measured from the NORMAL to the mirror.For reflection – The angle of incidence equals the angle of reflection.surface normalsameangleincident rayexit rayPrinciple of Least Time7ABtoo longshortest path;equal angles8PHY102Your eye focuses the diverging rays reflected by the mirror.The light rays appear to come from behind the mirror.An image is virtual if the light rays from a point on the object are directed as if they diverged from a point on the image, even though the rays do not actually pass through the image point.Mirror, Mirror, on the wall, how big do you have to be to see it all? The strange world of images.9“image” you“real” youThe speed of light10Light travel’s at a speed c in a vacuum.In an actual material, it travels a bit slower, at a velocity of v.The speed of light depends on the material through which it is traveling.DEFINITION – INDEX OF REFRACTION (or refractive index):1mediumnt transparaain light ofvelocity vacuumain light ofvelocity nIndex of Refraction11Notice12vacuumfcfcnfvvcn1For two materials12212211nndividennvacuumvacuumHuygen’s Principle13Each point on a wavefront actsas a secondary source of sphericalwaves that progress from thesource at the speed of light (whateverit may be).A spherical wave with very large radius,behaves as a plane wave.1415PHY102.Not there yet!16The Wave Nature of LightThe law of refraction is explained by Huygen’s PrincipleThe little wavelets move slower in medium 2 than in medium 1. Doing the tangent shows how the wave fronts bend.Some Geometry1700909018The Wave Nature of LightADC 2 BAD 1sin1v1tAD and sin2v2tAD2112121212221112212121//sinsin//sinsinnnncncvvtvtvnnnnncncvvIf medium 1 is air, thenn11 and v1c and 1n/nSnell’s Law of Refraction192211sinsinnn Law of Reflection21Another ViewOf Reflection(Huygen’s)20Both Together212223abcriticalbbcriticalaabnnSinnnSinnnn)90sin(0At the critical angle andbeyond, only reflection ispossible.Total Reflection – Optical Fiber2425A cross section of a submarine communications cable.1 - Polyethylene2 - Mylar tape3 - Stranded steel wires4 - Aluminium water barrier5 - Polycarbonate6 - Copper or aluminum tube7 - Petroleum jelly8 - Optical fibersLengths of 100 KM are possible before amplification is necessary.Thousands of conversations can be carried on a single fiber.26Waves on a string.dichroism2780%1% of opposite
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