Part II Electromagnetic Waves 1

So far 2 We have discussed The nature of EM waves Some of the properties of EM waves. Now we will discuss EM waves and optics Mirrors Lenses Applications

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Reflection & Refraction 4

Reflection 5

Light Reflection 6 Angles of incidence measured from the NORMAL to the mirror. For reflection – The angle of incidence equals the angle of reflection. surface normal same angle incident ray exit ray

Principle of Least Time 7 A B too long shortest path; equal angles

8 PHY102 Your 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” you

The speed of light 10 Light 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):

Index of Refraction 11

Notice 12 For two materials

Huygen’s Principle 13 Each point on a wavefront acts as a secondary source of spherical waves that progress from the source at the speed of light (whatever it may be). A spherical wave with very large radius, behaves as a plane wave.

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15 PHY102. Not there yet!

16 The Wave Nature of Light The law of refraction is explained by Huygen’s Principle The little wavelets move slower in medium 2 than in medium 1. Doing the tangent shows how the wave fronts bend.

Some Geometry 17

18 The Wave Nature of Light

Snell’s Law of Refraction 19 Law of Reflection

Another View Of Reflection (Huygen’s) 20

Both Together 21

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23 At the critical angle and beyond, only reflection is possible.

Total Reflection – Optical Fiber 24

25 A cross section of a submarine communications cable. 1 - Polyethylene 2 - Mylar tape 3 - Stranded steel wires 4 - Aluminium water barrier 5 - Polycarbonate 6 - Copper or aluminum tube 7 - Petroleum jelly 8 - Optical fiberscross sectionPolyethyleneMylarsteelAluminiumPolycarbonatePetroleum jellyOptical fibers Lengths of 100 KM are possible before amplification is necessary. Thousands of conversations can be carried on a single fiber.

26 Waves on a string.

dichroism 27 80% 1% of opposite polarization

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Mirage 32

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