The Electromagnetic Spectrum

A Mnemonic Device for the Waves in the Spectrum

• Rabbits (Radio Waves)Mate (Microwaves)In (Infrared)Very (Visible Light)Unusual (Ultraviolet Rays)eXpensive (X-Rays)Gardens (Gamma Rays)

Transmits Radio and TV Signals• Use continuous sine waves to transmit information (audio, video,

data• There are literally thousands of different radio waves (in the form of

sine waves) around you right now -- TV broadcasts, AM and FM radio broadcasts, police and fire radios, satellite TV transmissions, cell phone conversations, GPS signals, and so on

• Each different radio signal uses a different sine wave frequency, and that is how they are all separated.

• Any radio setup has two parts: The transmitter and the receiver • The transmitter takes some sort of message (it could be the sound

of someone's voice, pictures for a TV set, data for a radio modem or whatever), encodes it onto a sine wave and transmits it with radio waves. The receiver receives the radio waves and decodes the message from the sine wave it receives. Both the transmitter and receiver use antennas to radiate and capture the radio signal.

Radio waves

•Have the longest wavelength and the lowest frequency (least energy)

•Are used in communications, astronomy, weather forecasting, Radar, and microwaves

•Range in wavelength from larger than the earth to about 1 mm

•AM radio waves are about 1,000 feet (1,600 kilometers) in wavelength, while FM radio waves are only a few feet in wavelength

•Microwaves are a very short wavelength type of radio wave and range in size from 1 mm to 1 m

Astronomy

•study astronomical phenomena that are often invisible in other portions of the electromagnetic spectrum

•observe the Cosmic Microwave Background Radiation, by which we study the birth of our Universe in the Big Bang

•probe the “Dark Ages” before the onset of the first stars or galaxies, and study the earliest generation of galaxies

•analyze and explore the black holes that live at the hearts of most galaxies.

•Since radio waves penetrate dust, scientists use radio astronomy techniques to study regions that cannot be seen in visible light, such as the dust-shrouded environments where stars and planets are born, and the center of our Galaxy, the Milky Way

•allow astronomers to trace the location, density, and motion of the hydrogen gas that constitutes three-fourths of the ordinary matter in the Universe

Microwaves Used in Astronomy

• Cosmic Background Explorer (COBE) image of the cosmic microwave background, the pink and blue colors showing the tiny fluctuations in it

Cell Phones

A cell phone uses one radio frequency for talking and a second, separate frequency for listening allowing both people on the call to talk at once.

The carrier chops up the city into cells. Each cell is usually about 10 square miles (26 square kilometers). Each cell has a base station that consists of a tower and a small building containing the radio equipment.

The radio equipment picks up the radio waves sent by your phone and relays them to the person you are talking to. Conversely it radios their response to you. All cell phones have special codes associated with them. These codes are used to identify the phone, the phone's owner and the service provider.

Microwave Ovens• A microwave oven uses microwaves to heat food. • Microwaves are short wavelength radio waves. The

longer microwaves close to a foot in length, are the waves which heat our food in a microwave oven.

• Radio waves in this frequency are absorbed by water, fats and sugars. When they are absorbed they are converted directly into atomic motion -- heat.

• These waves are not absorbed by most plastics, glass or ceramics allowing heating of the food rather than the container

Weather Forecasting• Radio waves are sent from an antenna. • Objects in the air, such as raindrops, snow crystals, hailstones or

even insects and dust, scatter or reflect some of the radio waves back to the antenna.

• All weather radars, including Doppler, electronically convert the reflected radio waves into pictures showing the location and intensity of precipitation.

• Doppler radars also measure the frequency change in returning radio waves.

• Waves reflected by something moving away from the antenna change to a lower frequency, while waves from an object moving toward the antenna change to a higher frequency.

• The computer that's a part of a Doppler radar uses the frequency changes to show directions and speeds of the winds blowing around the raindrops, insects and other objects that reflected the radio waves.

Weather Radar

Doppler Radar

Weather Radar Picture

Other Uses for Radar

• Militarily to detect objects at a long-range• For missile guidance• To detect migration patterns of birds/insects• For air traffic control and navigation• By police to determine the speed of cars

This is how it works:

http://science.howstuffworks.com/radar2.htm

MRI’s Magnetic Resonance Imaging

•Are used to create images of inside of body without harmful ionizing radiation•Allows for detailed imaging of soft tissues which can be used to detect disease or injury . In addition scientists have used MRI images of the brain to study how the brain works.

MRI

• uses radio waves that interact with protons (the nuclei of hydrogen atoms)

• the radio signals are repeatedly turned on and off

• Energy in the radio waves is absorbed by different atoms in the target area and reflected back out of the body.

• When the radio waves are reflected off the patient's body, they generate new signals that are detected by the MRI machine

• These signals are sent to a MRI computer, which also collects all the signals from the giant coil, then combined to create the 3-D images.

MRI’s

Dangers of Radio Waves• Since they have a low frequency, they do not carry much

energy• Non-ionizing radiation• Investigations into cell phones and microwaves causing

cancer• No definitive studies

http://www.cancer.gov/cancertopics/factsheet/Risk/cellphones (look at #6)

http://www.cancer.gov/newscenter/tip-sheet-cancer-myths

Infrared Light

• Invisible to the eye but can be detected as warmth on the skin

• Divided into three regions: near infrared (nearest the visible spectrum), with wavelengths 0.78 to about 2.5 microns (a micron, is 10-6 metre); middle infrared, with wavelengths 2.5 to about 50 micrometres; and far infrared, with wavelengths 50 to 1,000 micrometres

Uses of Infrared

• Remote controls

• Heal injuries

• Night vision

• Thermal imaging

• Weather forecasting

• To study space- astronomy

Night Vision

• Night vision can work in two very different ways, depending on the technology used.

• Image enhancement - This works by collecting the tiny amounts of light, including the lower portion of the infrared light spectrum, that are present but may be imperceptible to our eyes, and amplifying it to the point that we can easily observe the image.

• Thermal imaging - This technology operates by capturing the upper portion of the infrared light spectrum, which is emitted as heat by objects instead of simply reflected as light. Hotter objects, such as warm bodies, emit more of this light than cooler objects like trees or buildings.

Uses for Night Vision

• The original purpose of night vision was to locate enemy targets at night. It is still used extensively by the military for that purpose, as well as for navigation, surveillance and targeting. Police and security often use both thermal-imaging and image-enhancement technology, particularly for surveillance. Hunters and nature enthusiasts use NVDs to maneuver through the woods at night.

• Detectives and private investigators use night vision to watch people they are assigned to track. Many businesses have permanently-mounted cameras equipped with night vision to monitor the surroundings.

• A really amazing ability of thermal imaging is that it reveals whether an area has been disturbed -- it can show that the ground has been dug up to bury something, even if there is no obvious sign to the naked eye. Law enforcement has used this to discover items that have been hidden by criminals, including money, drugs and bodies. Also, recent changes to areas such as walls can be seen using thermal imaging, which has provided important clues in several cases.

An image taken from a camera equipped with night vision

Thermal Imaging

In visible lightAs seen with infrared camera

Used in firefighting

To find victims in smoke filled rooms

And to locate hot spots like this subsurface fire at a landfill

Used in Astronomy

Visible lightWith infrared

Infrared light penetrates dust better allowing us to find new stars, galaxies, asteroids and quasars.Also allows us to study cool stars that do not give off much visible light.

Planetary nebulae are actually the remains of stars that once looked a lot like our sun. When sun-like stars die, they puff out their outer gaseous layers. These layers are heated by the hot core of the dead star, called a white dwarf, and shine with infrared and visible-light colors. Our own sun will blossom into a planetary nebula when it dies in about five

billion years.

In Spitzer's infrared view of the Helix nebula, the eye looks more like that of a green monster's. Infrared light from the outer gaseous layers is represented in blues and

greens. The white dwarf is visible as a tiny white dot in the center of the picture. The red color in the middle of the eye denotes the final layers of gas blown out when the star died

Diagnosis of Injury and Disease

Dangers of Infrared

• Like radio waves infrared photons do not carry much energy

• Non-ionizing radiation

• Only danger- overheating