1. Electromagnetic Waves
COS #18 and 19

2. What are electromagnetic waves
Waves that can travel through empty space and through matter.
They contain radiant energy
Transverse waves because the disturbance is perpendicular to the direction the wave travels.

3. Properties of Electromagnetic Waves
As frequency decreases, wavelength increases.
Electromagnetic waves are grouped based on wavelength and frequency.
Wave Speed
They travel at the speed of light/300,000km/s.
Frequency is a waves speed.
Speed of light/frequency=wavelength
Electromagnetic waves slow down when they encounter matter; therefore, they travel faster in empty space.

4. Electromagnetic Wave Energy
As the frequency increases the wave energy increases, unlike a mechanical wave, their energy is based on its amplitude.

5. Electromagnetic Spectrum
Is the entire range of electromagnetic waves with different frequencies and wavelengths.

6. How do you use electromagnetic waves
Radio Waves
are used to broadcast information by sending waves in all different directions. Broadcasting, television, radio, etc. became available when scientist learned how to use these waves.
Radio and Television
Carrier wave- EM wave that radio and television stations use to carry its sound or image signal
AM (amplitude modulation) change in the amplitude of a carrier wave (one way stations change its carrier wave).
FM (frequency modulation)- a change in frequency of a carrier wave.
Changes in frequency equals changes in sound.

7. Digital Signal
Analog is a smooth change in a carrier wave from high to low.
Digital signal changes in steps. Stations produce digital signals by changing different properties of a carrier wave.
Stations might send signals as pulses, or a pattern of starting and stopping.
The wave might have a code of high and low amplitudes.
Sounds and images send by digital signal are usually clearer than analog.

8. Transmission and Reception
Radio station broadcast:
Transmitter produces and sends out radio waves.
Antenna receives the wave and changes them back to sound.
Television transmits similar, but cable TV, waves travel through cables designed to carry radio waves.
FM waves tend to have higher frequencies and more energy than AM waves.
FM waves usually produce better sound quality.

9. Microwaves Good for sending and receiving signals.
Can carry more information than radio waves because their wavelength is shorter.
Pass easily through smoke, light rain, snow, and clouds.

10. Cell Phones Cells are regions of service
When a call is made on a cell phone a signal is sent to or received from a cell tower.
Electric circuits in the base station direct your signal to other towers.
A signal passes from cell to cell until it reaches the phone of the person you called.

11. Communication Satellites
Microwaves carry images and sounds from a satellite to your tv.
Satellite dishes receive a signal directly from a satellite.
A transmitter sends microwave signals to the satellite. The satellite can pass the signal to other satellites or to other places on earth.
GPS is a satellite that helps you find where you are going.
At least 24 GPS satellites continually orbit the earth, sending out signals about their orbits and the time.
Receivers analyze this information to calculate their location.

12. Infrared Waves Depend on an objects temperature
Vibrating molecules in any matter emit these waves.
Hotter objects emit Infrared waves with greater frequency and shorter wavelengths than cooler objects.

13. Infrared Imaging Thermal cameras detect infrared waves
These cameras convert invisible infrared waves or different temperatures, to different colors that they eye can interpret.
thermal imaging
Medical use to find poor circulation
Contractors use for buildings to find areas where excessive thermal energy is lost.

14. **X-Rays
Have more energy than ultraviolet waves and can pass through skin and muscle
Two important uses are:
Security (especially at court houses and airports)
Luggage scan at airport. They can pass through most materials except. metal.
They use computers to create images of the content in the luggage by measuring how different materials transmit the X-ray
Medical imaging.
X-rays pass through soft parts of your body but bone stops them.
The film turns dark when the X-rays strike them and light parts show where bone absorbed the X-ray

15. Gamma Rays
Extremely high energy rays are used to destroy diseased tissue.
Can be used to diagnose medical conditions.