Electromagnetic Spectrum
- [Rice University]
- The Electromagnetic Spectrum
In physics, electromagnetic radiation (EM radiation or EMR) refers to the waves (or their quanta, photons) of the electromagnetic field, propagating (radiating) through space, carrying electromagnetic radiant energy.
EM radiation spans an enormous range of wavelengths and frequencies. This range is known as the electromagnetic spectrum. The electromagnetic (EM) spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies. The EM spectrum is generally divided into seven regions, in order of decreasing wavelength and increasing energy and frequency. The common designations are: radio waves, microwaves, infrared (IR), visible light, ultraviolet (UV), X-rays and gamma rays. Typically, lower-energy radiation, such as radio waves, is expressed as frequency; microwaves, infrared, visible and UV light are usually expressed as wavelength; and higher-energy radiation, such as X-rays and gamma rays, is expressed in terms of energy per photon.
EM radiation is created when an atomic particle, such as an electron, is accelerated by an electric field, causing it to move. The movement produces oscillating electric and magnetic fields, which travel at right angles to each other in a bundle of light energy called a photon. Photons travel in harmonic waves at the fastest speed possible in the universe: 186,282 miles per second (299,792,458 meters per second) in a vacuum, also known as the speed of light. The waves have certain characteristics, given as frequency, wavelength or energy.
- Standard Units
A wavelength is the distance between two consecutive peaks of a wave. This distance is given in meters (m) or fractions thereof. Frequency is the number of waves that form in a given length of time. It is usually measured as the number of wave cycles per second, or hertz (Hz). A short wavelength means that the frequency will be higher because one cycle can pass in a shorter amount of time. Similarly, a longer wavelength has a lower frequency because each cycle takes longer to complete.
Do you know what a centimeter (cm) is? Or a kilogram (kg)? "Centi" and "kilo" are prefixes used to designate a certain number. "Centi" is one hundreth, and "kilo" is one thousand, so a centimeter is one hundreth of a meter. A kilogram is 1000 grams. In science, it is inconvenient to talk about very large or very small numbers so scientists abbreviate them. "Nano", (or "n" for short) means one billionth or 10-9. Wavelengths of optical light have units of nanometers (nm). One nm is equal to one billionth of a meter. "Micro" (abbreviated by the Greek letter mu or µ) is one millionth or 10-6. A micrometer, or one thousandth of a meter is sometimes called a "micron". "Milli" (m) is one thousandth or 10-3. "Centi" (c) is one hundreth or 10-2. "Kilo" is one thousand or 103. "Mega" (M) is one million or 106. The frequency of HFS is 99.1 MHz - that is 99.1 Megahertz. One billion is "giga" (G) or 109.
- Parts of the EM Spectrum
The EM spectrum is the range of all types of EM radiation. Radiation is energy that travels and propagates as it travels -- visible light from lights in your home and radio waves from radio stations are two types of electromagnetic radiation. Other types of electromagnetic radiation that make up the electromagnetic spectrum are microwaves, infrared, ultraviolet, X-rays, and gamma rays.
The following shows each part of the EM spectrum that you might encounter in your daily life.
- Radio: Your radio captures radio waves emitted by radio stations, bringing your favorite tunes. Radio waves are also emitted by stars and gases in space.
- Microwave: Microwave radiation will cook your popcorn in just a few minutes, but is also used by astronomers to learn about the structure of nearby galaxies.
- Infrared: Night vision goggles pick up the infrared light emitted by our skin and objects with heat. In space, infrared light helps us map the dust between stars.
- Visible: Our eyes detect visible light. Fireflies, light bulbs, and stars all emit visible light.
- Ultraviolet: Ultraviolet radiation is emitted by the Sun and are the reason skin tans and burns. "Hot" objects in space emit UV radiation as well.
- X-ray: A dentist uses X-rays to image your teeth, and airport security uses them to see through your bag. Hot gases in the Universe also emit X-rays.
- Gamma ray: Doctors use gamma-ray imaging to see inside your body. The biggest gamma-ray generator of all is the Universe.
- The Electromagnetic Spectrum
The electromagnetic spectrum includes, from longest wavelength to shortest: radio waves, microwaves, infrared, optical, ultraviolet, X-rays, and gamma-rays. The electromagnetic spectrum is the highway over which wireless operates, with multiple lanes capable of carrying traffic at different speeds.
Higher frequencies - and thus shorter wavelengths - are able to move more information per unit of time. As a wave’s frequency increases, the distance between each wave (the wavelength) gets shorter. Your phone measures wavelength to identify frequencies and to “hear” the data that a frequency is trying to transmit. But a stable, unchanging frequency can’t “talk” to your phone. It needs to be modulated by subtly increasing and decreasing the frequency rate. Your phone observes these tiny modulations by measuring changes in wavelength and then translates those measurements into data.
- Electromagnetic Radiation
In physics, electromagnetic radiation (EM radiation or EMR) refers to the waves (or their quanta, photons) of the electromagnetic field, propagating (radiating) through space, carrying electromagnetic radiant energy.
EM radiation spans an enormous range of wavelengths and frequencies. This range is known as the electromagnetic spectrum. The electromagnetic (EM) spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies. The EM spectrum is generally divided into seven regions, in order of decreasing wavelength and increasing energy and frequency. The common designations are: radio waves, microwaves, infrared (IR), visible light, ultraviolet (UV), X-rays and gamma rays. Typically, lower-energy radiation, such as radio waves, is expressed as frequency; microwaves, infrared, visible and UV light are usually expressed as wavelength; and higher-energy radiation, such as X-rays and gamma rays, is expressed in terms of energy per photon.
EM radiation is created when an atomic particle, such as an electron, is accelerated by an electric field, causing it to move. The movement produces oscillating electric and magnetic fields, which travel at right angles to each other in a bundle of light energy called a photon. Photons travel in harmonic waves at the fastest speed possible in the universe: 186,282 miles per second (299,792,458 meters per second) in a vacuum, also known as the speed of light. The waves have certain characteristics, given as frequency, wavelength or energy.
- Same Radio Waves as Gamma Rays
Are radio waves a completely different physical object than gamma rays? They are produced in different processes and detected in different ways, but they are not fundamentally different. Radio waves, gamma rays, visible light, and all other parts of the electromagnetic spectrum are electromagnetic radiation.
Electromagnetic radiation can be described by streams of smaller masses of particles called photons, each propagating in a wave-like pattern at the speed of light. Each photon contains a certain amount of energy. The different types of radiation are defined by the amount of energy in the photons. Radio waves have lower energy photons, microwave photons have a little more energy than radio waves, infrared photons have more energy, then visible light, ultraviolet rays, X-rays, and the highest-energy gamma rays.
[More to come ...]
