1. 18.2 The Electromagnetic Spectrum

2. The Waves of the Spectrum
The Electromagnetic Spectrum is the full range of frequencies of electromagnetic radiation
Includes radio waves, infrared waves, visible light, ultraviolet rays, X-rays, and gamma rays
Each type of wave has its own range of wavelengths and frequencies

3. Here is the Electromagnetic Spectrum with examples.
Emphasize the relationship between wavelength and frequency. . .especially since we will not be doing any of the math problems.
Here is the Electromagnetic Spectrum with examples.
Notice that as wavelength increases, frequency decreases.
And if wavelength decreases, the frequency will increase.

4. Radio Waves Longest wavelengths in the spectrum
Lowest frequencies in the spectrum
Used in radio and television technologies, as well as in microwaves and radars
Wavelengths: 1mm to 1000’s of km
Frequencies: 300,000MHz or less

5. Radio
Music and voices are changed into electronic signals that produce waves that are broadcast
Your radio receives the transmission and decodes it into sounds waves
Amplitude Modulation (AM)
Amplitude is varied, frequency stays the same
Frequency Modulation (FM)
Frequency is varied, amplitude stays the same
Electronic signals are “coded” onto radiowaves

6. How does radio broadcasting work?
Radio broadcasting: music and voices are changed into electronic signals that produce radio waves (AM or FM). The waves are transmitted and received by your radio, which decodes them into sounds waves. (see notes from the previous slide)
“Lost” station: a station is “lost” when the signal becomes to weak to detect. An FM station is more likely to be lost than an AM station because FM signals do not travel as far as AM along the earth’s curved surface. Particles in the upper atmosphere reflect the AM waves better than the FM waves.
-AM is lower frequency (535kHz to 1605kHz)
-FM is higher frequency (88MHz to 108MHz)
How does radio broadcasting work?
Have you ever “lost” a station on the radio?

7. Radiowaves carry info for picture and sound
Television
Radiowaves carry info for picture and sound
Location and weather can affect reception
Microwaves
Shortest wavelength radio waves
Used to cook/reheat food and for cell phone technology
TV: Broadcast process is similar to the radio (but now there is information for picture). Because weather and location can affect reception, most people prefer satellite transmission (TV broadcast sent to a satellite, then satellite retransmits to your home or to a cable provider).
Microwaves: Water and fat molecules in food absorb microwaves, increasing thermal energy. Generally only penetrate a few centimeters (that’s why you let the food stand and heat through conduction).
Cell phone transmission works similarly to radio broadcast.

8. Radio detection and ranging
Radar
Radio detection and ranging
Radio transmitter sends waves, waves reflect off an object, returning waves are interpreted by a receiver
In the picture above, the radar uses something called the Doppler effect. The radar sends waves towards the car, the waves bounce off the car and return back to the receiver, which will then analyze the information and give you your speed. The faster the car is going, the higher the frequency of the returning waves will be.

9. Infrared Rays
Used as a source of heat and to discover areas of heat differences
Higher frequency than radiowaves but lower than red light
You cannot see infrared radiation, but your skin senses it as warmth
Infrared wavelengths vary from 1mm to 750nm
Other examples include warming lamps for reptiles, warming lamps for food
The Thermograph above uses infrared sensors to create a color coded picture to show variations in temperature. They are used to see where a building might be losing heat, locate problems in the path of an electrical current, and for search and rescue during natural disasters.

10. Visible Light Is the visible part of the electromagnetic spectrum
Each wavelength corresponds to a specific frequency and a particular color
Red has the longest wavelength and lowest frequency
Violet has the shortest wavelength and highest frequency of the visible spectrum
If an increase in frequency increases the amount of energy in the wave, which color has the most energy?

11. Ultraviolet Rays Higher frequencies than violet light
Applications in health, medicine, and agriculture
Helps your body to produce vitamin D
Excessive exposure can cause sunburn, wrinkles, and eventually skin cancer
Kills microorganisms
A natural producer of UV radiation is the sun. People wear sunblock to reflect the UV radiation from the skin so they do not get sunburn.
The UV lamp above can be used to disinfect air in a building. We use a UV lamp to disinfect lab goggles.
UV lamps can also be used in plant nurseries during the winter to help plants grow

12. X-Rays Short wavelength, high frequency radiation
High energy that can penetrate matter
Used in medicine, industry, and transportation to take pictures of the inside of solid objects
X-rays of teeth and bone
Identification of contents
X-ray wavelengths are 12nm to 0.005nm
Teeth and bones will absorb x-rays and will appear white. Tissues will appear as dark, highly exposed areas. Too much exposure can damage or kill cells and tissue. For this reason, do you think you can get an unlimited number of x-rays? What precautions do you take when getting an x-ray?
X-rays can also be used to examine contents for dangerous materials.

13. Gamma Rays
Shortest wavelengths and highest frequencies in the spectrum
Has the most energy and greatest penetrating ability
Used in the medical field and in industrial situations as an inspection tool
Radiation therapy to kill cancer cells
Gamma ray wavelength is 0.005nm or less.
Expose to tiny amounts is tolerable, but overexposure can be deadly.
The picture on the left shows the penetrating power of gamma rays.
The picture on the right is an example of the use of gamma ray tracers that produce radiation in areas of elevated brain activity.