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Light is a WAVE

Light is a WAVE. 5.2.1 EM Spectrum & EM Waves. The Speed of Light (well, EM Waves really). Equation. EM Waves travel at 3.0 x 10 8 m/s (in a vacuum). They are slower in denser mediums. Speed of a medium depends on INDEX OF REFRACTION .

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Light is a WAVE

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  1. Light is a WAVE 5.2.1 EM Spectrum & EM Waves

  2. The Speed of Light (well, EM Waves really) Equation • EM Waves travel at 3.0 x 108 m/s(in a vacuum). • They are slower in denser mediums. • Speed of a medium depends on INDEX OF REFRACTION. • The closer the index is to 1.0 the faster the medium. Index of Refraction Speed of Light in vacuum Speed of Light in medium

  3. Example 1 What is the speed of light in a medium with an index of refraction of 2.0? Try it before going to the side with answers!

  4. Example 1 What is the speed of light in a medium with an index of refraction of 2.0?

  5. Example 2 The speed of light (f=5.09 × 1014Hz) in a trans­parent material is 0.75 times its speed in air. The absolute index of refraction of the material is ap­proximately • 0.75 • 1.3 • 2.3 • 4.0 Try it before going to the side with answers!

  6. Example 2 The speed of light (f=5.09 × 1014Hz) in a transparent material is 0.75 times its speed in air. The absolute index of refraction of the material is approximately • 0.75 • 1.3 • 2.3 • 4.0

  7. EM Wave Types Wavelength (m) Radio Microwave Infrared Visible Ultraviolet X-ray Gamma Ray An EM Wave’s type depends on its frequency/wavelength 103 10-2 10-5 10-7 10-8 10-10 10-12 About the size of… Building Human Honey Bee Pinpoint Protozoan Molecules Atoms Atomic Nuclei Freq (Hz) 104 108 1012 1015 1016 1018 1020 Temperature of bodies emitting the wavelength 1 K 100 K 10000 K 10 million K All objects emit EM radiation

  8. Color (Frequency) depends on Temperature https://www.youtube.com/watch?v=cPQeaAkAM_A

  9. EM Waves • Charged objects generate electric fields. • When they move, the field changes. • Changing electric fields produce MAGNETIC FIELDS. • Changing magnetic fields produce ELECTRIC FIELDS. • The E-fields and B-fields are perpendicular to each other. • Waving a charge back and forth generates an EM WAVE. Require a medium Do not require a medium

  10. Electromagnetic Wave Animation • https://www.youtube.com/watch?v=aCTRjVEmeC0

  11. Practice • The constellation of Orion is a highly recognizable arrangement of stars. There are two very distinct stars in this constellation, Betelgeuse which is a red star and Rigel which is a bluish star. The color red has a wavelength of about 750 nm and the color blue has a wavelength of about 400 nm. • Which color has the higher frequency? • Which star is hotter, Betelgeuse or Rigel? BLUE RIGEL

  12. Practice • An EM wave is traveling through outer space with a frequency of 8.0 x 1013 hertz. • What is the wavelength of this wave? v = fλ λ= v / f λ = (3.0 x 108 m/s) / (8.0 x 1013 Hz) λ = (3.8 x 10-6 m) • What type of wave is this? Infrared

  13. Practice • Listed below are the properties of several EM Waves. State whether the property given is a wavelength or frequency, then state which type of EM Wave it is. • 500000 hertz _______________ ______________ • 5.0 x 10-9 meter _______________ ______________ • 3.0 x 1013 hertz _______________ ______________ • 4.5 x 1014 hertz _______________ ______________ • 200 meters _______________ ______________ frequency radio wavelength X ray / UV frequency infrared (IR) visible light (red) frequency wavelength radio

  14. End of 5.2.1

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