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Electromagnetic Waves

Electromagnetic Waves. Physics 202 Professor Vogel Lecture 13. Reflection and Refraction. Angles measured from normal !! Angle of incidence ( q 1 ) Angle of reflection ( q 1 ’) Angle of refraction ( q 2 ) Law of Reflection q 1 ’ = q 1 Law of Refraction

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Electromagnetic Waves

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  1. Electromagnetic Waves Physics 202 Professor Vogel Lecture 13

  2. Reflection andRefraction • Angles measured from normal !! • Angle of incidence (q1) • Angle of reflection (q1’) • Angle of refraction (q2) • Law of Reflection • q1’ = q1 • Law of Refraction n2 sin q2 = n1 sin q1

  3. General Cases • n2 > n1 • Light is bent towards the normal • q2 < q1 • e.g. air to glass • n2 < n1 • Light is bent away from the normal • q2 > q1 • e.g. glass to air

  4. Index of Refraction • Every material has an index of refraction that determines its optical properties • Indices of refraction determine bending, by law of refraction • Index of refraction also determines the speed of light within the material • v=c/n • generally, v<c

  5. Consequences of Laws • Law of Reflection • The angle of reflection is equal to the angle of incidence (q1’ = q1) • Light changes direction when it reflects • but our vision expects light to travel on a straight line • we see images where light appears to come from

  6. Plane Mirror • q1’ = q1 • we see images where light appears to come from • Consider how light from your eye reflects from a mirror to get to your eye, so you can see it • repeat for light from your feet

  7. Images in Plane Mirror • Upright • Same distance behind mirror as object is in front • Generally “front” is side light comes from. • Same size as object • Left and right are reversed. • Cardinal directions aren’t reversed.

  8. Images in Plane MirrorBased on depth perception. Where do both the purple and the green rays appear to come from?

  9. Images in 2-D corner Reflector • Can see an image in each mirror • Light can also reflect from both mirrors, then back to you. • You see image of image 1 • Also see image of image 2 • Both should be same place

  10. Images in 2-D corner Reflector • Image of image • reflected twice • left and right exchanged twice • If you are right-handed, so is that image!

  11. Images in Curved Mirrors • Concave mirror • think “cave” • like bowl of spoon • image is upright and larger – if object is close • image is inverted and smaller – if object is far • Convex mirror • like back of spoon • image is upright and smaller – any distance

  12. Consequences of Laws • Law of Refraction n2 sin q2 = n1 sin q1 • Light changes direction when it refracts • but our vision expects light to travel on a straight line • we see images where light appears to come from • Demo

  13. Chromatic Dispersion • The index of refraction depends on the wavelength of light • In general, n is larger for shorter wavelengths • Blue light bent more than red • Incident white light is spread out into its constituent colors • Chromatic dispersion with raindrops causes rainbows

  14. Chromatic Dispersion

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