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Electromagnetic Spectrum Basics - Mastering Frequencies, Wavelengths, and Energy

Learn the fundamentals of the electromagnetic spectrum with Dr. H. Paul Shuch. This lesson covers deriving the speed of light, identifying visible light frequencies and wavelengths, converting between frequency and wavelength, and understanding Planck's Constant and energy per photon. Discover the continuum of waves from DC to Daylight and beyond, and explore the energy continuum from low to high energies.

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Electromagnetic Spectrum Basics - Mastering Frequencies, Wavelengths, and Energy

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  1. ElectromagneticSpectrum Basics Dr. H. Paul Shuch (rhymes with“luck”)

  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 that define the visible light spectrum • Converting between frequency and wavelength • Knowing Planck's Constant from memory • Calculating the energy per photon

  3. All waves behave Fundamentally Alike

  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 * 10^8 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. Waves, or particles? Actually, both!

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

  13. Remember red light? energy per photon e = h * νe = (6.626 * 10^-34 J * s) * (400 * 10^12 cycles/Sec)e = 2.65 * 10^-19 Joules

  14. How about violet? energy per photon e = h * νe = (6.626 * 10^-34 J * s) * (750 * 10^12 cycles/Sec)e = 4.97 * 10^-19 Joules

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

  16. Sunlight falling on the Earth: ~ 1 kW/m^2 (billions and billions of photons per second!)

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

  18. Review Exercises

  19. 1. What is the velocity of forward propagation of radiant electromagnetic energy in free space? c = 3 * 10^8 m/s

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

  21. 3. What is the value of Planck's Constant? k = 6.626 * 10^-34 J*s

  22. 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

  23. 5. How much energy is emitted by one hydrogen photon? e = h * ν e = (6.626 * 10^-34 J*s) * (1.420 * 10^9 Hz) e = 9.4 * 10^-25 Joules

  24. Did you score four or higher? You’ve mastered spectrum basics!

  25. Next lesson: Quantify those other portions of the spectrum

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