Electromagnetic Waves

What are they? Electromagnetic waves are energy which radiate from a source in a wave pattern – troughs and crests Waves can be measured in two ways…

Wavelength measures the actual distance from crest to crest. WAVELENGTH: is the measure of the distance from crest to crest – we use meters, centimeters, millimeters and smaller bits (down to NANOMETERS which is one millionth of a meter!) FREQUENCY: is the measure of how many crest and troughs pass by a given point in one second. We use HERTZ (1 hertz = 1 cycle per second) We can also simply talk about how much energy a wave carries. SHORT WAVELENGTHS and HIGHER FREQUENCIES carry more energy than long wavelengths and low frequencies.

Types of Electromagnetic Waves RADIO WAVES: radio waves are the longest in wavelength – from the length of a football field to the length of a football. We use radio waves primarily for communications and media – radio, TV and cellular phone transmissions. Radio waves are relatively low in energy.

MICROWAVES: microwaves are the next shortest wavelength waves. They are measured in centimeters. The longest microwaves, about 30cm long, are used for heating our food. Microwaves are used to transmit information, and also for Radar – both military and weather.

INFRARED WAVES: infrared waves are much shorter in wavelength – somewhere around the size of a pin-head. Infrared waves are thermal - felt as heat by our skin – when you feel the Sun on your skin in the summertime, that is IR. Infrared is used for thermal imaging. The shortest IR waves which we cannot feel are used in television remotes. MEOW…..

VISIBLE LIGHT: we are all familiar with visible light. Electromagnetic waves in this part of the spectrum have a length from 0.7 (red) to 0.4 (violet) micrometers. Our eyes can detect these waves and tell us what color they are by their differing wavelengths. Remember: white light contains all of the colors of the visible spectrum! We can split them into individual colors by using a prism.

ULTRAVIOLET (UV): UV waves carry more energy than visible light. They are around 30 nanometers in wavelength. Although we associate UV with Sun burns and skin cancer, scientists use UV emitted from distant stars and galaxies to learn more about them. Very little UV radiation gets through our atmosphere thanks to the ozone layer – but this means that astronomers must look at distant objects by using telescopes that orbit the Earth OUTSIDE of the atmosphere.

X-RAYS: in the 0.3 nanometer range we get X-rays. We all know what x-rays are used for medically, but scientists also study celestial objects using x- rays. A certain amount of x-ray radiation is considered safe, but frequent or long-term exposure can cause health problems, cell damage and cancers.

GAMMA RAYS: gamma rays have the highest energy and shortest wavelengths of all electromagnetic energy. They are emitted by some celestial events and objects, by nuclear explosions and by radioactive materials. Gamma rays can kill living cells – doctors use controlled gamma rays to treat cancer. Like x-rays and UV, astronomers use gamma waves to learn about distant space objects. Some companies use gamma radiation to kill bacteria in packaged food.

What energy gets to the Earth? Very little of the electromagnetic spectrum ever reaches the Earth’s surface due to our atmosphere. Visible light, shorter-wave IR and some longer wave UV, and radio waves can reach us, but the rest is absorbed by our atmosphere – which is good!