1. Properties of Electromagnetic Waves
Unit 6

2. Examples of Waves 1. X-ray machines 2. TV 3. Police Radar
4. Heat Lamps
5. Microwaves
6. Radiation
7. Color
8. Cell Phones

3. Electromagnetic Waves
Electromagnetic Waves—transverse waves consisting of changing electric fields and changing magnetic fields.
--They carry energy.
Different from mechanical waves in:
How they are produced.
How they travel.

4. How they are Produced Produced by constantly changing fields.
Produced when an electric charge vibrates or accelerates.
Electric Field– a region of space exerts electric forces on charged particles.
Magnetic Field—a region of space produces magnetic forces.

5. Electromagnetic Field

6. How They Travel
When electric fields change, they change magnetic fields.
And, when magnetic fields change, they change electric fields.
The energy of the magnetic fields and electric fields working together is the energy to make the wave.

7. Radiation
The transfer of energy by electromagnetic waves traveling through matter or space=electromagnetic radiation.
So, radios, microwaves, sun rays, and even color is radiation!

8. Michelson’s Experiment
American physicist who measured the speed of light most accurately.
Done in 1926
What’s happening in 1926?
Ford announces first 40-hour week
First rocket with rocket fuel
Houdini dies
First SAT test given to high schoolers

9. Michelson’s Experiment
On top of Mount Wilson in CA, he placed an 8-sided mirror.
He placed another mirror on top of Mount San Antonio (22 miles away)
He shined a light on the rotating mirror, it bounced off the other mirror on San Antonio, and then bounced back to Mount Wilson.
He knew how fast the rotating mirror was spinning, how far the light traveled so he calculated how fast the light traveled.
Michelson’s Experiment

11. That’s 186,000 miles per second
3.00 x 108 meters per second!
We call this “c”
That’s 186,000 miles per second
The speed of light is…

12. Wavelength & Frequency
All electromagnetic waves travel at the same speed in a vacuum.
Electromagnetic waves can vary in wavelength and frequency, so if one goes up, the other must go down…
Remember: The speed is always “c”

13. A radio station broadcasts a radio wave with a wavelength of 3
A radio station broadcasts a radio wave with a wavelength of 3.0 meters. What is the frequency of the wave?
Example