Electromagnetic Waves

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Electromagnetic Waves
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E-M waves

• Transverse
• Electric field and magnetic field- both
  perpendicular to propagation of the wave
• Can travel through a vacuum or a medium

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Frequency and E-M Spectrum

• Oscillations of electric charges at source
  determine the frequency
• Frequency determines type of wave

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Diffraction

• Bending around an obstacle
• Depends on the wavelength!
• Try diffraction in sound with a fan- if a sound
  diffracts well, it will be constant. If it
  doesnt diffract well, a fan will make it sound
  like pulses

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Polarization

• Most Light Sources Are Not Like This
• They Normally Consist of Waves In A Variety of
  Orientations
• This Is How They Would Look In A Head-On and an
  Oblique View

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Polarization

• Ordinary light vibrates in all planes
• Polarized light has a single plane of oscillation

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Polarization by filtering

• Polarizing filters contain long molecules where
  electrons only vibrate in one plane- only allow
  light waves vibrating in that plane to pass
  through

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Polarization by reflection

• When light reflects off a surface, the reflected
  wave vibrates most along the plane parallel to
  the surface

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Pairs of polarizing filters
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Uses of polarization

• Polarized sunglasses can be used to block the
  polarized glare (reflection) off a surface such
  as glass or water

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Polarizing filter
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Speed of Light

• 3.80x108m/s
• In a vacuum, is a constant c
• In one year light travels 9.46x1012 km 1 light
  year

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Speed of Light

• Astronomy is like looking back in time- light
  that we see from distant stars left those stars
  long ago
• The light from our sun takes about 9 minutes to
  reach us
• If we look at the most distant stars, we are
  looking at history closer to the big bang

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Wave Nature of Light

• Some diffraction (not as strong as sound)- thats
  why shadows have blurry edges
• Reflection
• Refraction
• Wavelength
• Doppler effect

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Color

• White light is combination of colors
• Color of light is property of its wavelength

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Color by addition

• Red, green, blue are primary colors
• Combine all 3 primary colors white light
• Combine any pair of primary colors secondary
  color
• Yellow, cyan, magenta