Waves & The Electromagnetic Spectrum

The shared properties

• All electromagnetic (EM) waves share four key features:
  • They are transverse waves
  • They all travel through a vacuum (and through air, water, glass, etc.)
  • They all travel at the same speed in a vacuum: c = 3.0 × 10⁸ m/s
  • They all obey the wave equation v = f × λ, so within the spectrum, longer wavelengths come with lower frequencies and vice versa

The seven bands of the spectrum

• The continuous electromagnetic spectrum is divided into seven named bands, listed below from longest wavelength / lowest frequency to shortest wavelength / highest frequency:
  1. Radio waves
  2. Microwaves
  3. Infrared
  4. Visible light
  5. Ultraviolet
  6. X-rays
  7. Gamma rays
• Mnemonics to lock the order in:
  • "Rock Musicians Invariably Vote United at X-mas (mostly Guitarists)"
  • "Roman Men Invented Very Unusual X-ray Guns"
• The frequency of an EM wave is inversely proportional to its wavelength; longer wavelength means lower frequency

The visible spectrum

• Of all seven bands, only visible light is picked up directly by the human eye, and even that occupies just a sliver of the full electromagnetic spectrum
• Within visible light, the colours run from longest to shortest wavelength as:
  • Red → Orange → Yellow → Green → Blue → Indigo → Violet
  • mnemonics: "Roy G. Biv" or "Richard Of York Gave Battle In Vain"
• Red has the longest wavelength and lowest frequency in the visible range
• Violet has the shortest wavelength and highest frequency in the visible range
• Other animals see beyond the visible band; bees pick up ultraviolet patterns on flowers, and some snakes detect infrared signatures of warm prey