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Electromagnetic Spectrum Basics

Electromagnetic Spectrum Basics. H. Paul Shuch Visiting Professor of Physics and Astronomy Lycoming College. Lesson Objectives Upon completion of this lesson, you will demonstrate mastery by: Deriving and recalling the speed of light

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Electromagnetic Spectrum Basics

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  1. ElectromagneticSpectrum Basics H. Paul Shuch Visiting Professor of Physics and Astronomy Lycoming College

  2. Lesson Objectives • Upon completion of this lesson, you will • demonstrate mastery by: • Deriving and recalling the speed of light • Identifying the frequencies and wavelengths • defining the RF, Microwave, and visible spectra • Converting between frequency and wavelength • Knowing Planck's Constant from memory • Calculating the energy and mass of a photon

  3. All waves behave Fundamentally Alike Gauss Faraday Ampere

  4. A continuum -- DC to Daylight . . . and Beyond!

  5. Visible Light Less than one octave

  6. l = Wavelength: Meters per Cycle n = Frequency: Cycles per Second (Hz)

  7. Speed of Light c = l n

  8. Red: 750 nm * 400 THz Violet: 400 nm * 750 THz c = l n (both equal 3 * 108 m/s!)

  9. (that’s three hundred million meters per second) (or three hundred kilometers per millisecond)

  10. The Rest of the Spectrum The long and the short of it

  11. The RF Spectrum ELF SLF ULF VLF LF M F H F VH F UH F SH F EH F

  12. RF Frequencies 3 30 300 3 30 300 3 30 300 3 30 300 Hz Hz Hz kHz kHz kHz MHz MHz MHz GHz GHz GHz ELF SLF ULF VLF LF M F H F VH F UH F SH F EH F

  13. RF Wavelengths 100 10 1 100 10 1 100 10 1 10 1 1 Mm Mm Mm km km km m m m cm cm mm l (m) = 300 / n (MHz) ELF SLF ULF VLF LF M F H F VH F UH F SH F EH F

  14. Microwave Bands 1 GHz 100 GHz Optical Components Lumped Components Distributed Components L S C X Ku mm

  15. Microwave Bands GHz: 1 2 4 8 12 18 100 L S C X Ku mm

  16. Microwave Bands l (cm) = 30 / n (GHz) GHz: 1 2 4 8 12 18 100 cm: 30 15 7.5 3.75 2.5 1.67 0.3 L S C X Ku mm

  17. Microwave Band’s Greatest Hits

  18. Photons: are they waves, or particles? Actually, both!

  19. Energy per Photon – Planck’s Law e = h n Where h = 6.626 * 10-34 Joules * seconds

  20. Remember red light? energy per photon e = h * νe = (6.626 * 10-34 J * s) * (400 * 1012 cycles/s)e = 2.65 * 10-19 Joules

  21. How about violet? energy per photon e = h * νe = (6.626 * 10-34 J * s) * (750 * 1012 cycles/s)e = 4.97 * 10-19 Joules

  22. How much energy per visible photon? Less than a billionth of a billionth of a Joule!

  23. Sunlight falling on Earth: ~ 1 kW/m2 (billions and billions of photons per second per square meter!)

  24. The spectrum as An energy continuum Left to right, Low to high energies

  25. Q: How are Photonslike quick Catholics? A: They have relativistic mass!

  26. (OK, so the rest mass of a photon is zero. However…) e = h n and e = m c2 so, h n = m c2 and relativistic mass: m = hn/c2

  27. Let’s calculate relativistic mass for a red photon: m = hn/c2 = (6.626 * 10-34 J * s) * (400 * 1012 Hz) (3 * 108 m/s)2 = 2.94 * 10-36 kg

  28. Is a red photon massive? (no, that’s only about a millionth of the mass of an electron!)

  29. Review Exercises

  30. 1. What is the velocity of forward propagation of radiant electromagnetic energy in free space? c = 3 * 108 m/s

  31. 2. From memory, what frequencies and wave-lengths define the edges of the visible light spectrum? n = 400 - 750 THz l = 750 - 400 nm

  32. 3. What is the value of Planck's Constant? h = 6.626 * 10-34 J*s

  33. 4. Interstellar hydrogen emits a strong spectral radiation line at a wavelength of 21 cm. To what frequency does this correspond? n = c / l n = 1420 MHz

  34. 5. Interstellar hydrogen emits a strong spectral radiation line in which segment of the electromagnetic spectrum? 1420 MHz is in the UHF spectrum, which extends from 300 to 3000 MHz.

  35. 6. Interstellar hydrogen emits a strong spectral radiation line in which microwave band? 21 cm is in L-band, which extends from 30 to 15 cm wavelength.

  36. 7. Hydrogen line receiving equipment would be composed of which type of components? All microwave circuitry incorporates distributed components.

  37. 8. How much energy is emitted by one hydrogen photon? e = h * ν e = (6.626 * 10-34 J*s) * (1.420 * 109 Hz) e = 9.4 * 10-25 Joules

  38. 9. How much does that hydrogen photon weigh? m = hn/c2 = (6.626 * 10-34 J * s) * (1.42 * 109 Hz) (3 * 108 m/s)2 = 1.05 * 10-41 kg

  39. 10. What is the most important characteristic of all electromagnetic waves? They all behave fundamentally alike.

  40. Did you score eight or higher? You’ve mastered spectrum basics!

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