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Chapter 27

Chapter 27. Light. Electromagnetic Waves. Electromagnetic Waves - waves carrying energy emitted by vibrating electrons Also know as… Light Radiation Photons. Model of Light Wave. Transverse (NOT longitudinal). Light Wave Speed. The speed of light is the same for all f orms of light.

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Chapter 27

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  1. Chapter 27 Light

  2. Electromagnetic Waves • Electromagnetic Waves - waves carrying energy emitted by vibrating electrons • Also know as… • Light • Radiation • Photons

  3. Model of Light Wave Transverse (NOT longitudinal)

  4. Light Wave Speed • The speed of light is the same for all forms of light. • It is 3.0 x 108 m/s (or 186,000 miles/s) in a vacuum. • Light speed decreases with different mediums.

  5. Electromagnetic Spectrum A range of light waves extending in wavelength from radio waves to gamma rays.

  6. The Visible Spectrum A range of light waves extending in wavelength from about 400 to 700 namometers. Basically, different wavelength = different color!

  7. To have an idea how long each wavelength is…

  8. Question • Is it correct to say that radio wave is a low-frequency light wave? • Yup. Low frequency = low energy

  9. Question • Why is the sun dangerous to view with the unprotected eye? • High frequency = high energy

  10. Chapter 28 Color

  11. The Colors We See… • We see the colors that are REFLECTED. • We don’t see the colors that are ABSORBED.

  12. Two opposite situations. • If ALL colors are Reflected (none absorbed)… • We see WHITE! • If NO colors are Reflected (all absorbed)… • We see BLACK! Absorbing light = increased heat Which part of the rabbit is warmer?

  13. Red paint • What primary color(s) is reflected? • RED!! That’s why we can see it! • In red paint, what primarycolor(s) is absorbed fromwhite light? • Yellow & Blue • Green Paint • What primary color(s) isreflected? • Yellow & Blue!! That’s why we see Green! • In green paint, what primarycolor(s) is absorbed fromwhite light? • Red

  14. Spectrum • Visible white light forms a pattern due to wavelength. • Red (longest wavelength = less energy) • Orange • Yellow • Green • Blue • Violet (shortest wavelength = more energy)

  15. The Kirchhoff-Bunsen Experiment • These two scientists found that burning chemicals over an open flame resulted in a spectrum with bright lines. • They found that each chemical element produced its own characteristic pattern of bright spectral lines.

  16. Emission Spectra • Hot gas produces a bright line emission spectrum. • Demo - hot hydrogen gas and diffraction gratings Emission Spectrum

  17. Hydrogen Helium Oxygen Carbon Every element can be “fingerprinted” by it spectra.

  18. The color (wavelength) of light emitted by a hot object changes with its temperature. • Glowing object colors: • Reddish coolest glowing object • Orange-ish • Yellowish • (White) • Bluish  hottest glowing object

  19. Emission Spectra of Hydrogen Discrete Emission Spectrum Slit Film Low Density Glowing Hydrogen Gas Prism Photographic Film

  20. Absorption Spectraof Hydrogen Discrete Emission Spectrum Discrete Absorption Spectrum Slit Hydrogen Gas Film White Light Source Prism Photographic Film

  21. Emission Spectra • Therefore, each element emits is own characteristic pattern of light frequencies.

  22. Chapter 29 Reflection & Refraction

  23.   Law of Reflection Angle of Reflection = Angle of Incidence

  24. Example Question… • What is the measure of angle theta? • 55 degrees

  25. Winning at Pool… • Imagine you areshooting at the mirror image of the red ball.

  26. What is wrong with this picture? • The girl in Manet'spainting, The Bar at the Folies-Bergeres, isstanding in front of a large mirror. • We see her back reflected and the face of a man sheseems to be talking to. • From the law of reflection what is wrong with thispainting?

  27. Refraction

  28. Index of Refraction • Higher index of refraction = more angle!

  29. Refraction Equations • n1 sinθ1 = n2 sinθ2 • n = v1/v2 (v = 3.00 x 106 m/s) • When light starts in air, n = sinθ1/sinθ2 • Because n1 = 1.00 in air or vacuum

  30. Chapter 31 Diffraction & Interference

  31. Water waves bend around obstacles  

  32. Diffraction • The bending of light around an obstacles or through a narrow slit in such a way that fringes of light and dark bans are produced.

  33. What does the size of the opening do to the waves? • Smaller opening = more bending!

  34. Wave Interference In some places the water wavefronts are in phase (bright spots). In other places the fronts overlap with peak and valley and interfere destructively (darker spots).

  35. Wave Interference

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