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Chapter 24

Chapter 24. Electromagnetic Waves. Maxwell’s Equation (Two Versions). Electromagnetic Wave. E. Light is represented by fluctuations in the magnetic and electric field called electromagnetic waves. EM wave is a consequence of the Maxwell’s Equation. B. Basic Facts about EM waves in vacuum.

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Chapter 24

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  1. Chapter 24 Electromagnetic Waves

  2. Maxwell’s Equation(Two Versions)

  3. Electromagnetic Wave E Light is represented by fluctuations in the magnetic and electric field called electromagnetic waves. EM wave is a consequence of the Maxwell’s Equation. B

  4. Basic Facts about EM waves in vacuum • Always travels at exactly the speed of light c. • E and B are always perpendicular. • E×B gives the direction of the wave. • |E|=|cB| • Two independent direction of polarization (later)

  5. The electromagnetic spectrum

  6. Why do we see colors?

  7. Question This is precisely the speed of light! Conclusive proof that light is a kind of EM wave.

  8. Bible? And God said, Let there be light, and there was light. - Genesis 1:3

  9. Light as a wave From this equation you can figure out the frequency from the wavelength or vice versa. You will do this many times in HW 24.

  10. Polarization (no need to memorize)

  11. Circular Polarization (Skip) Combination of vertical and horizontal polarization

  12. Polarizing Filters Electrons on long polymers (long molecules) that moves only in one direction, hence absorbing energy of the E field in that direction, but let the other direction through.

  13. Two filters

  14. Intensity Rules for Polarizer Make sure you know whether the light is polarized or unpolarized!

  15. Example with two filters

  16. Polarization by Reflection At the Brewster angle (or polarizing angle) θp, the reflected beam becomes polarized.

  17. Brewster’s Angle Complete polarization by reflection occurs when the reflected beam is perpendicular to the refracted beam.

  18. Brewster’s Angle Pictures taken with polarizers at different angles. The picture on the right has the reflected light removed by the polarizer to minimize reflection.

  19. Polarization by Scattering

  20. Huygen’s Principle Every point of a wave front may be considered the source of secondary wavelets that spread out in all directions with a speed equal to the speed of wave. The final wave is the sum of all these secondary wavelets.

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