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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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.