Electromagnetic radiation is the propagation of energy, in the form of light, through space. Much like ocean waves transfer energy through water, electromagnetic waves transfer energy through an electromagnetic field. Electromagnetic radiation travels in packets of energy called photons, and the energy in each photon depends upon the wave's frequency (but not amplitude). The radiation is created by the motion of charged particles and includes seven types: including radio waves, microwaves, infrared light, visible light, ultraviolet light, X-rays, and gamma rays. It is important to note that visible light is not fundamentally different from the other six types, except for the fact that it can be detected by the human eye.
Electromagnetic energy is simply the energy carried by electromagnetic waves often referred to as electromagnetic radiation. The energy travels at the speed of light (in fact, it is light!) in a vacuum, but travels slower through a medium. It can be emitted from objects, reflected by objects, or absorbed by objects. In the case of emission, the motion of charged particles within an object typically creates the wave (imagine the hot filament in a lightbulb). In the case of reflection, the wave bounces off a surface (imagine a mirror). And in the case of absorption, the wave is absorbed by an object and the charged particles within the object begin to move faster (imagine pavement absorbing sunlight on a hot day).
Like any wave, electromagnetic energy can be measured. The speed of its oscillation is called "frequency" and the lengths of the individual waves, measured from crest to crest, are called "wavelengths." Scientists have categorized the types of light, according to frequency and wavelength, into something called the electromagnetic spectrum. Electromagnetic radiation can range from wavelengths of several meters (radio waves) to wavelengths of picometres (gamma rays). The frequencies can range from hundreds of billions of Hertz (radio waves) all the way up to several septillion Hertz (gamma rays). As one travels up the spectrum, from low frequency to high frequency, the energy of each individual photon increases. This is why radio waves are considered harmless and X-rays and gamma rays are very dangerous. Photon energy is measured in electron volts, and it ranges from billionths of electron volts (radio waves) to millions of electron volts (gamma rays).
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Altogether, the electromagnetic spectrum can be ranked from low-frequency, low-energy, high wavelength all the way up to high-frequency, high-energy, low-wavelength. This ranking includes seven categories, listed in order as follows:
As you might have guessed, radio waves and microwaves have the least energy and are the least dangerous for humans. Meanwhile, X-rays and gamma rays have the most energy and can even cause cancer in humans.
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The two main properties that we use to categorize electrogenic radiation, the frequency of electromagnetic radiation and the electromagnetic radiation wavelength, are inverse. Because the speed of light is constant, a higher frequency will always mean a shorter wavelength and a higher wavelength will always mean a lower frequency.
Frequency can be defined as the number of waves that travel past a point each second. And wavelength can be defined as the length of a wave, measured from crest to crest or from trough to trough, at any given instant. Usually, these two quantities are related by the frequency formula: {eq}f = v/w {/eq}
In the above formula, f stands for frequency, v stands for wave speed, and w stands for wavelength. In the case of electromagnetic waves, v is always equal to the speed of light, at least in a vacuum. So solving for the wavelength at a given frequency, or for the frequency at a given wavelength, is a simple matter of multiplication or division. Thus, the frequencies and wavelengths of radio waves, visible light, and even X-rays are well-known quantities. This is important information to know when it comes to the construction of antennas, radio receivers, satellites, and other equipment that utilizes electromagnetic waves.
Additionally, a photon's energy can be calculated using the formula {eq}E=hf {/eq} where E stands for energy, f stands for frequency, and h stands for Planck's constant, one of the smallest constants in physics.
Electromagnetic energy comes in many forms. A microwave oven uses electromagnetic waves to vibrate water molecules and heats up your food. A cell phone sends electromagnetic waves to a tower, which sends them to a satellite, transmitting phone calls and text messages across the globe. In fact, all seven categories of electromagnetic radiation play important and very different roles in our everyday lives. Below are some electromagnetic radiation examples including descriptions and applications.
Radio waves are low-frequency, long-wavelength electromagnetic waves. They are the least energetic and least dangerous type of electromagnetic radiation. Their wavelength is defined as any wavelength above 1 millimeter, and their frequency is defined as any frequency below 300,000,000,000 Hz. Radio waves are used for everything from car stereos to cell phones to garage door openers.
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Microwaves have a higher frequency and lower wavelength than radio waves, but they are still generally thought of as low-energy and are not usually thought of as dangerous to humans. Their wavelength is defined as any wavelength between 1 millimeter and 25 micrometers, and their frequency is defined as any frequency between 300,000,000,000 and 10,000,000,000,000 Hertz. Microwaves are used by microwave ovens, of course, but also by some types of radar, Bluetooth headphones and speakers, GPS, and even Wi-Fi.
Beyond microwave frequencies is a type of radiation known as infrared light. The prefix infra is Latin for "below." Infrared means "below red" on the electromagnetic spectrum. Infrared wavelengths are defined as any wavelength between 25 micrometers and 2.5 micrometers, and their frequency is defined as any frequency between 10,000,000,000,000 and 400,000,000,000,000 Hertz. Infrared light is created by heat lamps, toasters, and even ovens to heat our food. Although, one should note that these devices can also create visible light when they are turned up to a high enough setting.
Visible light is not fundamentally different from infrared light. But it has a high enough frequency and low enough wavelength that it is detectable by the human eye. It comes in a variety of colors (red, orange, yellow, green, blue, indigo, etc.) that all correspond to different frequencies. But it is important to note that visible light is a distinctly human category; many snakes can see infrared light and many birds can see ultraviolet light. The wavelengths for visible light vary from 400 to 750 nanometers, and the frequencies are between 400,000,000,000,000 and 750,000,000,000,000 Hertz.
Beyond visible light, at just slightly higher frequencies and energies, is ultraviolet light. The prefix ultra comes from Latin, where it means "located beyond." Thus, ultraviolet light is located just beyond violet on the electromagnetic spectrum. However, one key difference between ultraviolet light and visible light is that ultraviolet light can be dangerous. At high frequencies and high amounts, ultraviolet light is capable of stripping electrons from the materials it strikes. This can damage human cells and tissues, causing sunburns and worse. The wavelengths for ultraviolet light vary from 1 to 400 nanometers, and the frequencies are between 1,000,000,000,000,000 and 100,000,000,000,000,000 Hertz.
X-rays are of a higher frequency, carry more energy, and have shorter wavelengths than ultraviolet light. They are very dangerous, capable of damaging and causing cancer in human cells. But they are also very useful. Because X-rays penetrate soft tissue more easily than bones, doctors use X-rays to identify fractures and assess many diseases. It is important that they are used safely, however. Typically, X-rays machines are turned on for only a brief moment and one's internal organs are shielded from the procedure using a lead blanket or something similar. The wavelengths for X-rays range from 1 nanometers to 1 picometer, and the frequencies are between 100,000,000,000,000,000 and 100,000,000,000,000,000,000 Hertz.
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Gamma rays are the highest-frequency type of electromagnetic radiation. They have a very small wavelength and each photon carries a large amount of energy. They are also very dangerous. Gamma rays can be extremely harmful to humans if the exposure is in high amounts. This is one of the reasons that nuclear waste is so harmful; it emits gamma rays for hundreds to thousands of years after nuclear fuel is spent. However, gamma rays can be useful in medicine (where it can kill cancer cells) and certain industries (where it is used for sterilization). The wavelengths for gamma rays are classified as anything less than 1 picometer, and the frequencies are anything above 100,000,000,000,000,000,000 Hertz.
Electromagnetic radiation is the propagation of electromagnetic waves (light) through space. It is created by the motion of charged particles and includes seven types: radio waves, microwaves, infrared light, visible light, ultraviolet light, X-rays, and gamma rays. The electromagnetic energy travels at the speed of light and can be emitted, reflected, or absorbed by various objects. Each photon carries a distinct amount of energy depending on its frequency (but not amplitude).
The electromagnetic spectrum is the range of frequencies and wavelengths of all types of electromagnetic waves. Radio waves have the lowest frequency, the longest wavelength, and the least amount of energy. On the other end of the spectrum, gamma rays have the highest frequency, shortest wavelength, and carry the most energy. Frequency can be defined as the number of waves that travel past a point each second, and wavelength can be defined as the length of a wave. The two properties are inverses of each other. The seven types of electromagnetic radiation are all fundamentally similar but have many different applications, from cell phones (radio waves) to GPS (microwaves) to killing cancer cells (gamma rays), and more.
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The seven types of electromagnetic energy are listed below, from lowest-frequency and lowest-energy to highest-frequency and highest-energy: radio waves, microwaves, infrared light, visible light, ultraviolet light, X-rays, gamma rays.
Three examples of electromagnetic energy are visible light (like the kind emitted by the sun), microwaves (like the kind used to warm our food), and X-rays (like the kind used at a doctor's office).
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