Electromagnetic Spectrum and EM Waves Light is a WAVE Electromagnetic Spectrum and EM Waves

EM Waves Light is part of the ELECTROMAGNETIC SPECTRUM EM WAVES are radiated by ALL objects at the SPEED OF LIGHT c = 3 x 108 m/s (in vacuum) Example #1 What is the wavelength of a radio wave traveling through outer space with a frequency of 5 x 104 Hz? v = fλ 3 x 108 m/s = (5 x 104 Hz) λ λ = 600 m

EM Wave Production Changing electric fields produce MAGNETIC FIELDS Changing magnetic fields produce ELECTRIC FIELDS The result is a self-propagating wave with perpendicular ELECTRIC and MAGNETIC fields These waves DO NOT REQUIRE A MEDIUM

What is the speed of light in lucite? EM Wave Speed Depends on the medium The “speed” of a medium depends on its density and is described by its INDEX OF REFRACTION (n) The closer the index is to 1, the faster the medium Example #2 What is the speed of light in lucite? n = 1.50 n = c / v 1.50 = (3 x 108 m/s) / v v = 2 x 108 m/s Index of Refraction = speed of light in vacuum speed of light in medium

Wein’s Law ALL objects emit EM radiation with a frequency directly related to their temperature EM Waves Sun  5630K Outer space  3K Humans  310K

Example #3 Red light has a wavelength of about 750 nm. Violet light has a wavelength of about 400 nm. Which color of light is emitted with a higher frequency? Shorter wavelength = higher frequency, so violet is higher Which star is hotter, Betelgeuse or Rigel? How can you tell? Wein’s Law says that hotter objects emit HIGHER frequencies, so blue stars are hotter – red ones are cooler Betelguese Rigel

EM Waves Summary EM waves travel at THE SPEED OF LIGHT. That speed depends on the MEDIUM OF TRAVEL EM waves do not require a MEDIUM. Low frequency EM waves (below ultra violet) are NON-IONIZING forms of radiation High frequency EM waves (ultra violet and higher) are IONIZING forms of radiation Dangerous to life  mutations, cancer, etc.