1. Light is a WAVE
EM Spectrum & EM Waves

2. The Speed of Light (well, EM Waves really)
EM Waves travel at 3.0 x 108 m/s (in a vacuum).
They are slower in denser mediums.
Speed of a medium depends on INDEX OF REFRACTION.
The closer the index is to 1.0 the faster the medium.
Equation
Index of Refraction
Speed of Light
in vacuum
in medium

3. Try it before going to the side with answers!
Example 1
What is the speed of light in a medium with an index of refraction of 2.0?
Try it before going to the side with answers!

4. Example 1
What is the speed of light in a medium with an index of refraction of 2.0?
n = 2.0
c = 3 x m/s
v = ?
v = 1.5 x 108 m/s

5. Try it before going to the side with answers!
Example 2
The speed of light (f=5.09 × 1014 Hz) in a trans­parent material is 0.75 times its speed in air. The absolute index of refraction of the material is ap­proximately
0.75
1.3
2.3
4.0
Try it before going to the side with answers!

6. Example 2
The speed of light (f=5.09 × 1014 Hz) in a transparent material is 0.75 times its speed in air. The absolute index of refraction of the material is approximately
0.75
1.3
2.3
4.0
n = ?
c = 3 x m/s
v = 0.75c
(because c is the speed of light in vacuum/air)
n =

7. Temperature of bodies emitting the wavelength
EM Wave Types
An EM Wave’s type depends on its frequency/wavelength
103
10-2
10-5
10-7
10-8
10-10
10-12
Wavelength (m)
Freq (Hz)
Temperature of bodies emitting the wavelength
1 K
100 K
10000 K
10 million K
104
108
1012
1015
1016
1018
1020
About the size of…
Building
Human
Honey Bee
Pinpoint
Protozoan
Molecules
Atoms
Atomic Nuclei
Radio
Microwave
Infrared
Visible
Ultraviolet
X-ray
Gamma Ray
All objects emit EM radiation

8. Color (Frequency) depends on Temperature

9. EM Waves Charged objects generate electric fields.
When they move, the field changes.
Changing electric fields produce MAGNETIC FIELDS.
Changing magnetic fields produce ELECTRIC FIELDS.
The E-fields and B-fields are perpendicular to each other.
Waving a charge back and forth generates an EM WAVE.
Require a medium
Do not require a medium

10. Electromagnetic Wave Animation

11. Practice
The constellation of Orion is a highly recognizable arrangement of stars. There are two very distinct stars in this constellation, Betelgeuse which is a red star and Rigel which is a bluish star. The color red has a wavelength of about 750 nm and the color blue has a wavelength of about 400 nm.
Which color has the higher frequency?
Which star is hotter, Betelgeuse or Rigel?
BLUE
RIGEL

12. Practice
An EM wave is traveling through outer space with a frequency of 8.0 x 1013 hertz.
What is the wavelength of this wave?
v = fλ
λ= v / f
λ = (3.0 x 108 m/s) / (8.0 x 1013 Hz)
λ = (3.8 x 10-6 m)
What type of wave is this?
Infrared

13. Practice
Listed below are the properties of several EM Waves. State whether the property given is a wavelength or frequency, then state which type of EM Wave it is.
hertz _______________ ______________
5.0 x 10-9 meter _______________ ______________
3.0 x 1013 hertz _______________ ______________
4.5 x 1014 hertz _______________ ______________
200 meters _______________ ______________
frequency
radio
wavelength
X ray / UV
frequency
infrared (IR)
frequency
visible light (red)
wavelength
radio

14. End of 5.2.1