1. A “Light” Day of Notes

2. Maxwell’s Equations
J. C. Maxwell developed 4 equations which govern all of electricity and magnetism.
These 4 equations make light work.
You do not need to know these.

3. Maxwell’s Equations

4. Spectrum
Just like sound is classified according to its pitch, there are different kinds of light, classified by their frequency.
The speed of light is constant.*
Therefore, a certain frequency of light will always have the same wavelength.
We can also classify light by wavelength.

6. Electromagnetic Spectrum

7. Radio Lowest Frequency EM waves AM (up to ~1 MHz) FM (90~100 MHz)
Shortwave (in between)
VHF (TV)
UHF (TV)
Cell Phone reception
Radar

8. Microwave (-wave) The Gigahertz (GHz) range Wavelength in cm.
Microwave ovens operate at 2.45 GHz
This is a special frequency to cause resonance in water

9. Infrared (IR) Wavelength in “micrometers” (m)
Most commonly referred to as heat
Hot objects radiate their thermal energy away.
Up to a few hundred degrees, the radiant energy is in the IR range
If we could see IR light, we would all shine brightly

10. More Infrared

11. Visible The light we can see A tiny portion of the EM spectrum
Red ( = 700 nm)
Orange
Yellow
Green
Blue
Indigo
Violet ( = 450 nm)

12. Ultraviolet (UV) Wavelength as low as 10 nm Used to kill germs
Black Lights
The part of sunlight that causes sunburn and skin cancer
Partially blocked by the ozone layer

13. X-Ray These can be useful, but also dangerous
Wavelength between 10 nm and 10 pm
That is from 10 billionths of a meter to 10 trillionths of a meter

14. Gamma Ray ( ray)  < 10 pm High energy Dangerous
Remember Gamma radiation from last semester

15. Practice What is the wavelength of AM radio wave 960 kHz?
f = 960,000 Hz
c = 3 × 108 m/s
 = c/f
 = 3 × 108 m/s ÷ 960,000 Hz
 = 312 m

16. Practice
What is the frequency of a “shortwave” radio wave 120 meters long?
 = 120 m
c = 3 × 108 m/s
f = c/
f = 3 × 108 m/s ÷ 120 m
f = 2,500,000 Hz = 2,500 kHz = 2.5 MHz

17. Practice
What is the wavelength of an FM radio wave? These waves are approximately 100 MHz (100 × 106 Hz).
f = 100,000,000 Hz
c = 3 × 108 m/s
 = c/f
 = 3 × 108 m/s ÷ 100,000,000 Hz
 = 3 m

18. Practice
What is the wavelength of a microwave in a microwave oven? These waves are 2.45 GHz (2.45 × 109 Hz).
f = 2,450,000,000 Hz
c = 3 × 108 m/s
 = c/f
 = 3 × 108 m/s ÷ 2,450,000,000 Hz
 = 0.12 m = 12 cm

19. Conclusion -- Quiz Wed. (4/29)
Electromagnetic Spectrum
Radio
Microwave
Infrared
Visible
Roy G Biv
Ultraviolet
X Ray
Gamma Ray
Visible Spectrum
Red
Orange
Yellow
Green
Blue
Indigo
Violet

20. Assignment
Chapter 12 vocabulary