Notes

The Electromagnetic

Spectrum

What are Electromagnetic Waves?◦ Waves that carry energy as electricity and

magnetism at the speed of light. The light we can see is an electromagnetic

wave, but the other types are invisible to humans.

The different types of waves have different frequencies and wavelengths, but all types travel at the speed of light.

Electromagnetic Waves

Electromagnetic Spectrum

Radio waves have the longest wavelength and lowest frequency in the spectrum.◦ Wavelength ranges from 10,000 km to less than a

meter. They carry radio and TV signals around

Earth. Radio waves from outer space are picked up

by radio telescopes and used in studies of the universe.

Radio Waves

Wavelengths range from 30 cm to 1 millimeter.

A use of microwaves involves radar, which is a way of locating planes and ships, as well as people speeding.

Another use of microwaves is cooking.◦ Microwaves in microwave ovens cause water

molecules in food to spin. As they spin, the molecules hit nearby molecules making them spin and therefore move faster, and so the food warms.

Microwaves

This part of the spectrum is also called radiant heat; we can feel this part of the spectrum as heat.

Infrared rays are slightly longer waves than visible red light.

ALL objects emit infrared radiation, which comes from the thermal motion of the molecules.

The warmer an object is, the more the atoms and molecules move, so the more infrared radiation it emits.

Infrared Waves

This is the very narrow band of the entire spectrum that we can see.

The wavelength of visible light is very short; the range is from 7 x 10-7 m to 4 x 10-7 m.

Each wavelength in the spectrum is representative of a color; the red wavelengths are longer and the violet are shorter.

When all the wavelengths strike your eyes at the same time, white is perceived. ◦ Technically, white is not a color; it is the combination

of all the colors of the visible light spectrum.

Visible Light

UV rays are slightly shorter than visible violet light and carry more energy.

Although these waves are invisible to humans, some insects can see UV waves.

Our Sun emits light at all the different wavelengths in electromagnetic spectrum, but it is ultraviolet waves that are responsible for causing our sunburns.

Though some ultraviolet waves from the Sun penetrate Earth's atmosphere, most of them are blocked from entering by various gases like Ozone. Some days, more ultraviolet waves get through our atmosphere. Scientists have developed a UV index to help people protect themselves from these harmful ultraviolet waves.

Ultraviolet Rays

X-rays are high-energy waves that pass through flesh but not bone, so are therefore used in medicine to check for broken bones.

They were discovered by Wilhelm Roentgen in 1895.

X-rays can be used in the treatment of cancer because it kills faster growing cancer cells more readily than normal cells.

X-rays are also used to inspect canned goods and computer chips. Scientists use them to inspect crystalline structure.

X-Rays

Gamma rays have the shortest wavelength and highest frequency and carry the most energy out of all the ER spectrum.

Like ultraviolet light and x-rays, gamma rays can kill microorganisms and are used to sterilize food and other objects, like medical equipment and instruments.

Gamma rays are also a treatment against cancer, but can be harmful to humans as well.

Gamma Rays