The Electromagnetic Spectrum

The Electromagnetic Spectrum

1. Discovery of waves

   • Isaac Newton discovered the visible spectrum in 1666
     • The visible spectrum is the range of light waves that can be seen by the human eye
   • 1800 William Herschel discovered infrared (heat) waves.
     • Used a row of thermometers to measure the temperature of different parts of the visible spectrum
     • He noticed that the temperature increased slightly as he moved the thermometers to the red end of the visible spectrum
     • When he moved them into the dark region beyond the red end, the temperature increased rapidly.
   • 1801 Johann Ritter discovered ultraviolet rays.
   • 1888 Heinrich Hertz discovered radio waves
   • 1895 Wilhelm Rontgen discovered X-rays
   • 1900 Paul Villard doscovered gamma rays

2. Electromagnetic waves

   • energy from the sun travels to the earth in the form of electromagnetic waves.
     • These waves form the electromagnetic spectrum in which they are ordered according to their frequency and wavelength.

3. Absorption and Emission

   • Microwaves to monitor rain - absorption
   • Infrared sensors - detect temperature differences. (emission)
   • X-rays to see bone fracture - absoption
   • Ultraviolet to detect forged bank notes - absoption

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