Electromagnetic Waves

by Madison Hadfield

What kind of disturbance creates an EM wave?

Electromagnetic waves are produced by a vibrating electric charge.

What are two ways that EM waves are different from mechanical waves?

First off, mechanical waves require a medium to travel through, while electromagnetic waves can travel through a vacuum. In addition, electromagnetic waves move with very high velocity, but mechanical waves propagate much slower.

Different Ranges of the EM Spectrum

Radio

Radio waves usually cover 1 cm to 1 km. The frequencies of these waves span from 30 gigahertz to 300 kilohertz. Since these are the longest waves, they have the lowest energy and are associated with the lowest temperatures. Radio waves have the least amount of energy on the electromagnetic spectrum, less than 2 x 10^-24 J. Radio waves are used everyday in radios and radar and navigation systems.

Microwave

Microwave waves have a wavelength that is from 1 x 10^-3 m to 1 x 10^-1 m. These waves have frequencies between 3 x 10^9 Hz to 3 x 10^11 Hz. The energy levels of these waves are between 2 x 10^-24 J and 2 x 10^-22 J. Microwave waves are used in microwave ovens and in communication satellites.

Infrared

Infrared waves have a wavelength that spans from 7 x 10^-7 m to 1 x 10^-3 m. The frequencies of infrared waves are between 3 x 10^11 Hz and 4 x 10^14 Hz. The energy levels of infrared waves spans from 2 x 10^-22 J to 3 x 10^-19 J. Infrared waves are used in remote controls and in infrared heat lamps, which can be used to heat bathrooms and keep food warm.

Visible Light

Visible light covers the range of wavelengths from 400 – 700 nm (from the size of a molecule to a protozoan), or 4 x 10^-7 m to 7 x 10^-7 m. Our sun emits the most of its radiation in the visible range, which our eyes perceive as the colors of the rainbow. Our eyes are sensitive only to this small portion of the electromagnetic spectrum. The frequencies of visible light span from 4 x 10^14 Hz to 7.5 x 10^14 Hz. The energy levels of visible light cover 3 x 10^-19 J to 5 x 10^-19 J. Visible light waves are used everyday in light bulbs and are used daily by the human eye in order to see the lights of the electromagnetic spectrum.

Ultra-violet

Ultra-violet waves have wavelengths of 10 – 310 nm, or 1 x 10^-8 m to 4 x 10^-7 m (about the size of a virus). Young, hot stars produce a lot of ultraviolet light and bathe interstellar space with this energetic light. The frequencies of these waves range from 7.5 x 10^14 Hz to 3 x 10^16 Hz. The energy levels of ultra-violet waves are from 5 x 10^-19 J to 2 x 10^-17 J. Ultra-violet waves are emitted by the sun and are the cause of sun burns. They are also used in UV lamps in hospitals to sterilize equipment.

X-ray

X-rays range in wavelength from 0.01 – 10 nm, or from 1 x 10^-11 m to 1 x 10^-8 m (about the size of an atom). They are generated, for example, by super-heated gas from exploding stars and quasars, where temperatures are near a million to ten million degrees. The frequencies of X-rays span from 3 x 10^16 Hz to 3 x 10^19 Hz. The energy levels of X-ray waves cover 2 x 10^-17 J to 2 x 10^-14 J. X-ray waves are used by doctors to take X-rays of people's teeth. X-rays are also used in airports to scan the contents of travelers' luggage.

Gamma Ray

Gamma rays have the shortest wavelengths, < 0.01 nanometers, or < 1 x 10^-11 m. (about the size of an atomic nucleus). They have the highest frequency and the most energetic region of the electromagnetic spectrum. Gamma rays can result from nuclear reactions and from processes taking place in objects such as pulsars, quasars, and black holes. The frequencies of gamma rays are more than 3 x 10^19 Hz, and the energy levels are more than 2 x 10^-14 J. Gamma rays are used in medicine to kill and treat certain types of cancers and tumors. In addition, gamma rays can be used to kill harmful bacteria in food.

Light: Crash Course Astronomy #24