PHYSICS ELECTROMAGNETIC SPECTRUM

• Electromagnetic spectrum


  The entire distribution of electromagnetic radiation according to frequency or wavelength
• Electromagnetic spectrum includes


  • Radio waves
  • Microwaves
  • Infrared
  • Optical
  • Ultraviolet
  • X-rays
  • Gamma-rays
• Frequency


  Measured in cycles per second, or Hertz
• Wavelength


  Measured in meters
• Energy


  Measured in electron volts
• The three quantities (frequency, wavelength, energy) for describing EM radiation are related to each other in a precise mathematical way
• Radio waves


  • Longest wavelengths in the electromagnetic spectrum, ranging from 10^-1 m to 10^4 m
  • Heinrich Hertz proved their existence in the late 1880s
• Radio spectrum bands


  • Extremely Low Frequency (ELF)
  • Very Low Frequency (VLF)
  • Low Frequency (LF)
  • Medium Frequency (MF)
  • High Frequency (HF)
  • Very High Frequency (VHF)
  • Ultra High Frequency (UHF)
  • Super High Frequency (SHF)
  • Extremely High Frequency (EHF)
• Microwaves


  • Shorter than radio waves with wavelengths measured in centimeters
  • Discovered by James Clerk Maxwell in 1864
  • Easily absorbed by water molecules, used in microwave ovens
  • Frequencies ranging from about 1 GHz to 300 GHz, wavelengths of about 30 cm to 1 mm
• Microwaves can cause cataracts, so it's a bad habit to put your face near a microwave oven
• Infrared waves


  • Part of the electromagnetic spectrum, people can detect them as heat
  • Wavelengths range from 7x10^-7 m to 10^-3 m
  • Discovered by Sir William Herschel around 1800
  • Used in remote controls, alarm systems, and night vision
• Too much exposure to infrared rays can lead to overheating
• Visible light


  • The part of the electromagnetic spectrum visible to the unaided eye
  • Extends from the short wave violet (λ=4x10^-7 m) to the long wave red (λ=7.6x10^-7 m)
  • Approximate wavelengths of different colors: Violet 410 nm, Blue 470 nm, Green 550 nm, Yellow 590 nm, Orange 610 nm, Red 760 nm
  • Indigo is not usually distinguished as a separate color, being so close to blue and violet
• The range in wavelengths of the visible light spectrum was discovered by Isaac Newton in the 17th century, although it had been discovered four centuries earlier in the 13th century by Roger Bacon
• Ultraviolet (UV) rays


  • Wavelengths ranging from 6x10^-10 m to 4x10^-7 m
  • Major source is the sun, also emitted by special lamps
  • Used to detect forged bank notes
  • Too much exposure can burn skin and produce suntan
  • Three main types: UVA (longest wavelength), UVB, UVC (shortest wavelength)
  • UVC and some UVB absorbed by Earth's ozone layer, so most UV is UVA with some UVB
• 1. rays


  • Thousand times shorter than the shortest visible light, have very high frequencies
  • Wavelength range of 0.01–10 nm, frequencies of 3x10^16–3x10^19 Hz, energies of 100 eV to 100 keV
  • Soft X-rays can penetrate soft substances like flesh and bones, hard X-rays are more penetrating and used in industry
  • Discovered in 1895 by Wilhelm Conrad Röentgen
• Gamma rays


  • Given off by radioactive materials like cobalt-60 and cesium-137
  • Highly penetrating due to very short wavelengths ranging from less than 10^-14 m to 10^-10 m
  • Discovered by Paul Villard in 1900
  • Smallest wavelengths and most energy of any wave in the electromagnetic spectrum
  • Produced by the hottest and most energetic objects in the universe, as well as nuclear explosions, lightning, and radioactive decay