Electromagnetic spectrum From Wikipedia, the free encyclopedia This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (November 2007) Class Freq uency 300 EHz γ Energy 1 pm 1.24 MeV Gamma rays 30 EHz HX Wave length 10 pm 124 keV Hard X-rays 3 EHz 100 pm 12.4 keV SX Soft X-rays 300 PHz 30 PHz EUV NUV 1 nm 1.24 keV 10 nm 124 eV 3 PHz 100 nm 12.4 eV Extreme ultraviolet Near ultraviolet Visible 300 THz NIR 1.24 eV Near Infrared 30 THz MIR 1 μm 10 μm 124 meV Mid infrared 3 THz 100 μm 12.4 meV FIR Far infrared 300 GHz EHF Extremely high frequency 30 GHz SHF VHF 1 cm 124 μeV Super high frequency Radio waves UHF 1 mm 1.24 meV 3 GHz 1 dm 12.4 μeV 300 MHz 1 m 1.24 μeV Ultra high frequency Very high frequency 30 MHz 10 m 124 neV HF MF LF High frequency 3 MHz 100 m 12.4 neV 300 kHz 1 km 1.24 neV Medium frequency Low frequency 30 kHz VLF 10 km 124 peV Very low frequency 3 kHz 100 km 12.4 peV VF / ULF Voice frequency 300 Hz SLF 1 Mm 1.24 peV Super low frequency 30 Hz 10 Mm ELF 124 feV Extremely low frequency 3 Hz 100 Mm 12.4 feV Sources: File:Light spectrum.svg    The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object has a different meaning, and is instead the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object. The electromagnetic spectrum extends from below the low frequencies used for modern radio communication togamma radiation at the short-wavelength (high-frequency) end, thereby covering wavelengths from thousands ofkilometers down to a fraction of the size of an atom. The limit for long wavelengths is the size of the universe itself, while it is thought that the short wavelength limit is in the vicinity of the Planck length. Until the middle of last century it was believed by most physicists that this spectrum was infinite and continuous. Most parts of the electromagnetic spectrum are used in science for spectroscopic and other probing interactions, as ways to study and characterize matter. In addition, radiation from various parts of the spectrum has found many other uses for communications and manufacturing (see electromagnetic radiation for more applications). Contents [hide] 1 History of electromagnetic spectrum discovery 2 Range of the spectrum 3 Rationale for spectrum regional names 4 Types of radiation o 4.1 Boundaries o 4.2 Regions of the spectrum o 4.3 Radio frequency o 4.4 Microwaves o 4.5 Terahertz radiation o 4.6 Infrared radiation o 4.7 Visible radiation (light) o 4.8 Ultraviolet radiation o 4.9 X-rays o 4.10 Gamma rays 5 See also 6 Notes and references 7 External links History of electromagnetic spectrum discovery For most of history, visible light was the only known part of the electromagnetic spectrum. The ancient Greeksrecognized that light traveled in straight lines and studied some of its properties, including reflection and refraction. Over the years the study of light continued and during the 16th and 17th centuries there were conflicting theories which regarded light as either a wave or a particle. The first discovery of electromagnetic radiation other than visible light came in 1800, when William Herscheldiscovered infrared radiation. He was studying the temperature of different colors by moving a thermometer through light split by a prism. He noticed that the highest temperature was beyond red. He theorized that this temperature change was due to "calorific rays" which would be in fact a type of light ray that could not be seen. The next year, Johann Ritter worked at the other end of the spectrum and noticed what he called "chemical rays" (invisible light rays that induced certain chemical reactions) that behaved similar to visible violet light rays, but were beyond them in the spectrum. They were later renamed ultraviolet radiation. Electromagnetic radiation had been first linked to electromagnetism in 1845, when Michael Faraday noticed that the polarization of light traveling through a transparent material responded to a magnetic field (see Faraday effect). During the 1860s James Maxwell developed four partial differential equations for the electromagnetic field. Two of these equations predicted the possibility of, and behavior of, waves in the field. Analyzing the speed of these theoretical waves, Maxwell realized that they must travel at a speed that was about the known speed of light. This startling coincidence in value led Maxwell to make the inference that light itself is a type of electromagnetic wave. Maxwell's equations predicted an infinite number of frequencies of electromagnetic waves, all traveling at the speed of light. This was the first indication of the existence of the entire electromagnetic spectrum. Maxwell's predicted waves included waves at very low frequencies compared to infrared, which in theory might be created by oscillating charges in an ordinary electrical circuit of a certain type. Attempting to prove Maxwell's equations and detect such low frequency electromagnetic radiation, in 1886 the physicist Heinrich Hertz built an apparatus to generate and detect what is now called radio waves. Hertz found the waves and was able to infer (by measuring their wavelength and multiplying it by their frequency) that they traveled at the speed of light. Hertz also demonstrated that the new radiation could be both reflected and refracted by various dielectric media, in the same manner as light. For example, Hertz was able to focus the waves using a lens made of tree resin. In a later experiment, Hertz similarly produced and measured the properties of microwaves. These new types of waves paved the way for inventions such as thewireless telegraph and the radio. In 1895 Wilhelm Röntgen noticed a new type of radiation emitted during an experiment with an evacuated tube subjected to a high voltage. He called these radiations x-rays and found that they were able to travel through parts of the human body but were reflected or stopped by denser matter such as bones. Before long, many uses were found for them in the field of medicine. The last portion of the electromagnetic spectrum was filled in with the discovery of gamma rays. In 1900 Paul Villard was studying the radioactive emissions of radium when he identified a new type of radiation that he first thought consisted of particles similar to known alpha and beta particles, but with the power of being far more penetrating than either. However, in 1910, British physicist William Henry Bragg demonstrated that gamma rays are electromagnetic radiation, not particles, and in 1914, Ernest Rutherford (who had named them gamma rays in 1903 when he realized that they were fundamentally different from charged alpha and beta rays) and Edward Andrade measured their wavelengths, and found that gamma rays were similar to X-rays, but with shorter wavelengths and higher frequencies. Range of the spectrum Electromagnetic waves are typically described by any of the following three physical properties: the frequency f, wavelength λ, or photon energy E. Frequencies observed in astronomy range from 2.4×1023 Hz (1 GeV gamma rays) down to the local plasma frequency of the ionized interstellar medium (~1 kHz). Wavelength is inversely proportional to the wave frequency, so gamma rays have very short wavelengths that are fractions of the size of atoms, whereas wavelengths on the opposite end of the spectrum can be as long as the universe. Photon energy is directly proportional to the wave frequency, so gamma ray photons have the highest energy (around a billion electron volts), while radio wave photons have very low energy (around a femtoelectronvolt). These relations are illustrated by the following equations: where: c = 299,792,458 m/s is the speed of light in vacuum and h = 6.62606896(33)×10−34 J s = 4.13566733(10)×10−15 eV s is Planck's constant. Whenever electromagnetic waves exist in a medium with matter, their wavelength is decreased. Wavelengths of electromagnetic radiation, no matter what medium they are traveling through, are usually quoted in terms of the vacuum wavelength, although this is not always explicitly stated. Generally, electromagnetic radiation is classified by wavelength into radio wave, microwave, terahertz (or sub-millimeter) radiation, infrared, the visible region is perceived as light,ultraviolet, X-rays and gamma rays. The behavior of EM radiation depends on its wavelength. When EM radiation interacts with single atoms and molecules, its behavior also depends on the amount of energy per quantum (photon) it carries. Spectroscopy can detect a much wider region of the EM spectrum than the visible range of 400 nm to 700 nm. A common laboratory spectroscope can detect wavelengths from 2 nm to 2500 nm. Detailed information about the physical properties of objects, gases, or even stars can be obtained from this type of device. Spectroscopes are widely used inastrophysics. For example, many hydrogen atoms emit a radio wave photon that has a wavelength of 21.12 cm. Also, frequencies of 30 Hz and below can be produced by and are important in the study of certain stellar nebulae and frequencies as high as 2.9×1027 Hz have been detected from astrophysical sources. Rationale for spectrum regional names Electromagnetic radiation interacts with matter in different ways across the spectrum. These types of interaction are so different that historically different names have been applied to different parts of the spectrum, as though these were different types of radiation. Thus, although these "different kinds" of electromagnetic radiation form a quantitatively continuous spectrum of frequencies and wavelengths, the spectrum remains divided for practical reasons related to these qualitative interaction differences. Region of the spectrum Main interactions with matter Radio Collective oscillation of charge carriers in bulk material (plasma oscillation). An example would be the oscillatory travels of the electrons in anantenna. Microwave through farinfrared Plasma oscillation, molecular rotation Near infrared Molecular vibration, plasma oscillation (in metals only) Visible Molecular electron excitation (including pigment molecules found in the human retina), plasma oscillations (in metals only) Ultraviolet Excitation of molecular and atomic valence electrons, including ejection of the electrons (photoelectric effect) X-rays Excitation and ejection of core atomic electrons, Compton scattering (for low atomic numbers) Gamma rays Energetic ejection of core electrons in heavy elements, Compton scattering (for all atomic numbers), excitation of atomic nuclei, including dissociation of nuclei High-energy gamma rays Creation of particle-antiparticle pairs. At very high energies a single photon can create a shower of high-energy particles and antiparticles upon interaction with matter. Types of radiation The electromagnetic spectrum Boundaries A discussion of the regions (or bands or types) of the electromagnetic spectrum is given below. Note that there are no precisely defined boundaries between the bands of the electromagnetic spectrum; rather they fade into each other like the bands in a rainbow (which is the subspectrum of visible light). Radiation of each frequency and wavelength (or in each band) will have a mixture of properties of two regions of the spectrum that bound it. For example, red light resembles infrared radiation in that it can excite and add energy to some chemical bonds and indeed must do so to power the chemical mechanisms responsible for photosynthesis and the working of the visual system. Regions of the spectrum The types of electromagnetic radiation are broadly classified into the following classes: 1. 2. 3. 4. 5. 6. 7. 8. Gamma radiation X-ray radiation Ultraviolet radiation Visible radiation Infrared radiation Terahertz radiation Microwave radiation Radio waves This classification goes in the increasing order of wavelength, which is characteristic of the type of radiation. While, in general, the classification scheme is accurate, in reality there is often some overlap between neighboring types of electromagnetic energy. For example, SLF radio waves at 60 Hz may be received and studied by astronomers, or may be ducted along wires as electric power, although the latter is, in the strict sense, not electromagnetic radiation at all (see near and far field). The distinction between X-rays and gamma rays is partly based on sources: the photons generated from nuclear decay or other nuclear and subnuclear/particle process, are always termed gamma rays, whereas X-rays are generated by electronic transitions involving highly energetic inner atomic electrons. In general, nuclear transitions are much more energetic than electronic transitions, so gamma-rays are more energetic than X-rays, but exceptions exist. By analogy to electronic transitions, muonic atom transitions are also said to produce X-rays, even though their energy may exceed 6 megaelectronvolts (0.96 pJ), whereas there are many (77 known to be less than 10 keV (1.6 fJ)) low-energy nuclear transitions (e.g., the 7.6 eV (1.22 aJ) nuclear transition of thorium-229), and, despite being one million-fold less energetic than some muonic X-rays, the emitted photons are still called gamma rays due to their nuclear origin. The convention that EM radiation that is known to come from the nucleus, is always called "gamma ray" radiation is the only convention that is universally respected, however. Many astronomical gamma ray sources (such as gamma ray bursts) are known to be too energetic (in both intensity and wavelength) to be of nuclear origin. Quite often, in high energy physics and in medical radiotherapy, very high energy EMR (in the >10 MeV region) which is of higher energy than any nuclear gamma ray, is not referred to as either X-ray or gamma-ray, but instead by the generic term of "high energy photons." The region of the spectrum in which a particular observed electromagnetic radiation falls, is reference frame-dependent (due to the Doppler shift for light), so EM radiation that one observer would say is in one region of the spectrum could appear to an observer moving at a substantial fraction of the speed of light with respect to the first to be in another part of the spectrum. For example, consider the cosmic microwave background. It was produced, when matter and radiation decoupled, by the de-excitation of hydrogen atoms to the ground state. These photons were from Lyman series transitions, putting them in the ultraviolet (UV) part of the electromagnetic spectrum. Now this radiation has undergone enough cosmological red shift to put it into the microwave region of the spectrum for observers moving slowly (compared to the speed of light) with respect to the cosmos. Radio frequency Main articles: Radio frequency, Radio spectrum and Radio waves Radio waves generally are utilized by antennas of appropriate size (according to the principle of resonance), with wavelengths ranging from hundreds of meters to about one millimeter. They are used for transmission of data, via modulation. Television, mobile phones, wireless networking, and amateur radio all use radio waves. The use of the radio spectrum is regulated by many governments through frequency allocation. Radio waves can be made to carry information by varying a combination of the amplitude, frequency, and phase of the wave within a frequency band. When EM radiation impinges upon a conductor, it couples to the conductor, travels along it, and induces an electric current on the surface of that conductor by exciting the electrons of the conducting material. This effect (the skin effect) is used in antennas. Microwaves Main article: Microwaves Plot of Earth's atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation. The super-high frequency (SHF) and extremely high frequency (EHF) of microwaves are on the short side of radio waves. Microwaves are waves that are typically short enough (measured in millimeters) to employ tubular metalwaveguides of reasonable diameter. Microwave energy is produced with klystron and magnetron tubes, and with solid state diodes such as Gunn and IMPATT devices. Microwaves are absorbed by molecules that have a dipole momentin liquids. In a microwave oven, this effect is used to heat food. Low-intensity microwave radiation is used in Wi-Fi, although this is at intensity levels unable to cause thermal heating. Volumetric heating, as used by microwave ovens, transfers energy through the material electromagnetically, not as a thermal heat flux. The benefit of this is a more uniform heating and reduced heating time; microwaves can heat material in less than 1% of the time of conventional heating methods. When active, the average microwave oven is powerful enough to cause interference at close range with poorly shielded electromagnetic fields such as those found in mobile medical devices and poorly made consumer electronics. Terahertz radiation Main article: Terahertz radiation Terahertz radiation is a region of the spectrum between far infrared and microwaves. Until recently, the range was rarely studied and few sources existed for microwave energy at the high end of the band (sub-millimeter waves or so-called terahertz waves), but applications such as imaging and communications are now appearing. Scientists are also looking to apply terahertz technology in the armed forces, where high-frequency waves might be directed at enemy troops to incapacitate their electronic equipment. Infrared radiation Main article: Infrared radiation The infrared part of the electromagnetic spectrum covers the range from roughly 300 GHz to 400 THz (1 mm - 750 nm). It can be divided into three parts: Far-infrared, from 300 GHz to 30 THz (1 mm - 10 μm). The lower part of this range may also be called microwaves. This radiation is typically absorbed by so-called rotational modes in gas-phase molecules, by molecular motions in liquids, and by phonons in solids. The water in Earth's atmosphere absorbs so strongly in this range that it renders the atmosphere in effect opaque. However, there are certain wavelength ranges ("windows") within the opaque range that allow partial transmission, and can be used for astronomy. The wavelength range from approximately 200 μm up to a few mm is often referred to as "submillimeter" in astronomy, reserving far infrared for wavelengths below 200 μm. Mid-infrared, from 30 to 120 THz (10 - 2.5 μm). Hot objects (black-body radiators) can radiate strongly in this range, and human skin at normal body temperature radiates strongly at the lower end of this region. This radiation is absorbed by molecular vibrations, where the different atoms in a molecule vibrate around their equilibrium positions. This range is sometimes called the fingerprint region, since the mid-infrared absorption spectrum of a compound is very specific for that compound. Near-infrared, from 120 to 400 THz (2,500 - 750 nm). Physical processes that are relevant for this range are similar to those for visible light. The highest frequences in this region can be detected directly by some types of photographic film, and by many types of solid state image sensors for infrared photography and videography. Visible radiation (light) Main article: Visible spectrum Above infrared in frequency comes visible light. The Sun emits its peak power in the visible region, although integrating the entire emission power spectrum through all wavelengths shows that the Sun emits slightly more infrared than visible light. By definition, visible light is the part of the EM spectrum to which the human eye is the most sensitive. Visible light (and near-infrared light) is typically absorbed and emitted by electrons in molecules and atoms that move from one energy level to another. This action allows the chemical mechanisms that underly human vision and plant photosynthesis. The light which excites the human visual system is a very small portion of the electromagnetic spectrum. A rainbow shows the optical (visible) part of the electromagnetic spectrum; infrared (if it could be seen) would be located just beyond the red side of the rainbow withultraviolet appearing just beyond the violet end. Electromagnetic radiation with a wavelength between 380 nm and 760 nm (400–790 terahertz) is detected by the human eye and perceived as visible light. Other wavelengths, especially near infrared (longer than 760 nm) and ultraviolet (shorter than 380 nm) are also sometimes referred to as light, especially when the visibility to humans is not relevant. White light is a combination of lights of different wavelengths in the visible spectrum. Passing white light through a prism splits it up into the several colors of light observed in the visible spectrum between 400 nm and 780 nm. If radiation having a frequency in the visible region of the EM spectrum reflects off an object, say, a bowl of fruit, and then strikes the eyes, this results in visual perception of the scene. The brain's visual system processes the multitude of reflected frequencies into different shades and hues, and through this insufficiently-understood psychophysical phenomenon, most people perceive a bowl of fruit. At most wavelengths, however, the information carried by electromagnetic radiation is not directly detected by human senses. Natural sources produce EM radiation across the spectrum, and technology can also manipulate a broad range of wavelengths. Optical fiber transmits light that, although not necessarily in the visible part of the spectrum (it is usually infrared), can carry information. The modulation is similar to that used with radio waves. Ultraviolet radiation Main article: Ultraviolet The amount of penetration of UV relative to altitude in Earth's ozone Next in frequency comes ultraviolet (UV). The wavelength of UV rays is shorter than the violet end of the visible spectrum but longer than the X-ray. UV in the very shortest range (next to X-rays) is capable even of ionizing atoms (see photoelectric effect), greatly changing their physical behavior. At the middle range of UV, UV rays cannot ionize but can break chemical bonds, making molecules to be unusually reactive. Sunburn, for example, is caused by the disruptive effects of middle range UV radiation on skin cells, which is the main cause of skin cancer. UV rays in the middle range can irreparably damage the complex DNA molecules in the cells producing thymine dimers making it a very potentmutagen. The Sun emits significant UV radiation (about 10% of its total power), including extremely short wavelength UV that could potentially destroy most life on land (ocean water would provide some protection for life there). However, most of the Sun's most-damaging UV wavelengths are absorbed by the atmosphere and ozone layer before they reach the surface. The higher energy (shortest wavelength) ranges of UV (called "vacuum UV") are absorbed by nitrogen and, at longer wavelengths, by simple diatomic oxygen in the air. Most of the UV in the mid-range of energy is blocked by the ozone layer, which absorbs strongly in the important 200–315 nm range, the lower part of which is too long to be absorbed by ordinary dioxygen in air. The very lowest energy range of UV between 315 nm and visible light (called UV-A) is not blocked well by the atmosphere, but does not cause sunburn and does less biological damage. However, it is not harmless and does cause oxygen radicals, mutation and skin damage. See ultraviolet for more information. X-rays Main article: X-rays After UV come X-rays, which, like the upper ranges of UV are also ionizing. However, due to their higher energies, X-rays can also interact with matter by means of the Compton effect. Hard X-rays have shorter wavelengths than soft X-rays. As they can pass through most substances with some absorption, X-rays can be used to 'see through' objects with thicknesses less than equivalent to a few meters of water. One notable use in this category is diagnostic X-ray images in medicine (a process known as radiography). X-rays are useful as probes in high-energy physics. In astronomy, the accretion disks around neutron stars and black holes emit X-rays, which enable them to be studied. X-rays are also emitted by the coronas of stars and are strongly emitted by some types of nebulae. However, X-ray telescopes must be placed outside the Earth's atmosphere to see astronomical X-rays, since the atmosphere of Earth is a radiation shield with areal density of 1000 grams per cm2, which is the same areal density as 1000 centimeters or 10 meters thickness of water. This is an amount sufficient to block almost all astronomical X-rays (and also astronomical gamma rays—see below). Gamma rays Main article: Gamma rays After hard X-rays come gamma rays, which were discovered by Paul Villard in 1900. These are the most energetic photons, having no defined lower limit to their wavelength. Inastronomy they are valuable for studying high-energy objects or regions, however like with X-rays this can only be done with telescopes outside the Earth's atmosphere. Gamma rays are useful to physicists thanks to their penetrative ability and their production from a number of radioisotopes. Gamma rays are also used for the irradiation of food and seed for sterilization, and in medicine they are occasionally used in radiation cancer therapy. More commonly, gamma rays are used for diagnostic imaging in nuclear medicine, with an example being PET scans. The wavelength of gamma rays can be measured with high accuracy by means of Compton scattering. Gamma rays are first and mostly blocked by Earth's magnetosphere then by the atmosphere. Electromagnetic Spectrum The electromagnetic (EM) spectrum is the range of all types of EM radiation. Radiation is energy that travels and spreads out as it goes – the visible light that comes from a lamp in your house and the radio waves that come from a radio station are two types of electromagnetic radiation. The other types of EM radiation that make up the electromagnetic spectrum are microwaves, infrared light,ultraviolet light, X-rays and gamma-rays. You know more about the electromagnetic spectrum than you may think. The image below shows where you might encounter each portion of the EM spectrum in your day-to-day life. The electromagnetic spectrum from lowest energy/longest wavelength (at the top) to highest energy/shortest wavelength (at the bottom). (Click image for a larger version.) 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 theUniverse 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. Is a radio wave the same as a gamma ray? Are radio waves completely different physical objects than gamma-rays? They are produced in different processes and are detected in different ways, but they are not fundamentally different. Radio waves, gamma-rays, visible light, and all the other parts of the electromagnetic spectrum are electromagnetic radiation. Electromagnetic radiation can be described in terms of a stream of mass-less particles, called photons, each traveling 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 the amount of energy found in the photons. Radio waves have photons with low energies, microwave photons have a little more energy than radio waves, infrared photons have still more, then visible, ultraviolet, X-rays, and, the most energetic of all, gamma-rays. Measuring electromagnetic radiation Electromagnetic radiation can be expressed in terms of energy, wavelength, orfrequency. Frequency is measured in cycles per second, or Hertz. Wavelength is measured in meters. Energy is measured in electron volts. Each of these three quantities for describing EM radiation are related to each other in a precise mathematical way. But why have three ways of describing things, each with a different set of physical units? Comparison of wavelength, frequency and energy for the electromagnetic spectrum. (Click image for a larger version.) The short answer is that scientists don't like to use numbers any bigger or smaller than they have to. It is much easier to say or write "two kilometers" than "two thousand meters." Generally, scientists use whatever units are easiest for the type of EM radiation they work with. Astronomers who study radio waves tend to use wavelengths or frequencies. Most of the radio part of the EM spectrum falls in the range from about 1 cm to 1 km, which is 30 gigahertz (GHz) to 300 kilohertz (kHz) in frequencies. The radio is a very broad part of the EM spectrum. Infrared and optical astronomers generally use wavelength. Infrared astronomers use microns (millionths of a meter) for wavelengths, so their part of the EM spectrum falls in the range of 1 to 100 microns. Optical astronomers use bothangstroms (0.00000001 cm, or 10-8 cm) and nanometers (0.0000001 cm, or10-7 cm). Using nanometers, violet, blue, green, yellow, orange, and red light have wavelengths between 400 and 700 nanometers. (This range is just a tiny part of the entire EM spectrum, so the light our eyes can see is just a little fraction of all the EM radiation around us.) The wavelengths of ultraviolet, X-ray, and gamma-ray regions of the EM spectrum are very small. Instead of using wavelengths, astronomers that study these portions of the EM spectrum usually refer to these photons by their energies, measured in electron volts (eV). Ultraviolet radiation falls in the range from a few electron volts to about 100 eV. X-ray photons have energies in the range 100 eV to 100,000 eV (or 100 keV). Gamma-rays then are all the photons with energies greater than 100 keV. Show me a chart of the wavelength, frequency, and energy regimes of the spectrum Why do we put telescopes in orbit? The Earth's atmosphere stops most types of electromagnetic radiation from space from reaching Earth's surface. This illustration shows how far into the atmosphere different parts of the EM spectrum can go before being absorbed. Only portions of radio and visible light reach the surface. (Credit: STScI/JHU/NASA) Most electromagnetic radiation from space is unable to reach the surface of the Earth. Radio frequencies, visible light and some ultraviolet light makes it to sea level. Astronomers can observe some infrared wavelengths by putting telescopes on mountain tops. Balloon experiments can reach 35 km above the surface and can operate for months. Rocket flights can take instruments all the way above the Earth's atmosphere, but only for a few minutes before they fall back to Earth. For long-term observations, however, it is best to have your detector on an orbitingsatellite and get above it all! Updated: March 2013 Lesson: Visible Light and the Electromagnetic Spectrum Contributed by: Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder Summary During this lesson, the electromagnetic spectrum is explained and students learn that visible light makes up only a portion of this wide spectrum. Students also learn that engineers use electromagnetic waves for many different applications. Engineering Connection Relating science and/or math concept(s) to engineering Engineers use many types of electromagnetic waves. Gamma radiation is emitted by fuel rods in nuclear power plants, x-rays are used to see inside our bodies, ultraviolet light can be used to sanitize things, microwaves are used to cook, and radio waves allow us to communicate over large distances. Contents 1. Pre-Req Knowledge 2. Learning Objectives 3. Introduction/Motivation 4. Background 5. Vocabulary 6. Associated Activities 7. Lesson Closure 8. Attachments 9. Assessment Figure 1. The electromagnetic spectrum. copyright 10. Extensions 11. References Grade Level: 4 (3-5) Lessons in this Unit: 12345678 Time Required: 20 minutes Lesson Dependency :None Keywords: light, electromagnetic spectrum, radiation, visible spectrum, transverse wave My Rating: Avg Rating: Not Yet Rated. Teacher Experiences | Share your experience! Related Curriculum subject areas curricular units activities Physical Science Sound and Light Building a Fancy Spectrograph The Visual Spectrum Educational Standards : Colorado: Science International Technology and Engineering Educators Association: Technology Next Generation Science Standards: Science Does this curriculum meet my state's standards? Select state or (Inter)national) Submit Pre-Req Knowledge (Return to Contents) This lesson follows Lessons 1-6 of the Sound and Light Unit. Learning Objectives (Return to Contents) After this lesson, students should be able to: Explain that light can be considered an electromagnetic wave. Give two examples of how engineers use electromagnetic waves. Explain that we can only see a small portion of all electromagnetic waves. Introduction/Motivation (Return to Contents) *Note: These concepts might be very difficult to visualize; if possible, create transparencies of the lesson figures for students to look at during class discussions. Let's think about our brave adventurers for a minute – who remembers what Angie and Harmon need to do next to find the treasure? That's right – they want to use lights underwater to find the sunken treasure ship. But first, they need to learn something about light waves so that they can choose the right kind of lights to use in their exploration. When we learned about sound, we discovered that sound travels in waves. Light can also be thought of as a wave – light is a form of anelectromagnetic wave. That's a big word, so let's write it on the board. An electromagnetic wave is a type of wave that can travel through empty space... Yes, you heard correctly, empty space. Unlike sound waves, which need "something" to travel through (for example, water or air), electromagnetic waves are able to travel through "emptiness" or a vacuum. This picture (show Electromagnetic Transparency #1– in the Attachments section) shows different kinds of electromagnetic waves. Engineers use electromagnetic waves for many different purposes. Gamma rays (nuclear power plant radiation), x-rays, light, microwaves, and radio waves (including cell phone waves) are all electromagnetic waves. What makes all these waves different from each other are their wavelengths and frequencies. Who would like to remind the class what frequency is? That's right! The frequency of a wave is the number of times a crest occurs each second. Some waves have really big — or even really small — frequencies. If a wave has a higher frequency (many waves in a certain amount of time), it has more energy. And, if a wave has a smaller frequency (fewer waves in a certain amount of time), it has less energy. Let's look at another picture (show Electromagnetic Transparency #2) to see if we can figure out which waves have the most energy. Which waves do you think are the most powerful? That's right! gamma waves have very high frequencies and, consequently, have a lot of energy. This extreme amount of energy is one reason why gamma waves are very dangerous if improperly used. Have any of you ever had an x-ray? X-rays are not as strong as gamma rays, but they are still very powerful. A sunburn? Have any of you ever burned your skin when out in the hot sun (or overcast as well) too long? Sunburns come from ultraviolet light, which we cannot see, but can still burn our skin. Radio waves and microwaves have a smaller frequency, so they are much less powerful than x-rays or ultraviolet light. Waves are fascinating, that's for sure! We know that waves with high frequencies have a lot of energy. And, the waves that have smaller frequencies have less energy — think of these wave types as energetic waves that move very fast and lazy waves that move slow. Did you know that we cannot see most electromagnetic waves? The small section of the spectrum with the waves that we can see is called the visible spectrum, and the wavelengths that we can see allow us to see the colors of red, orange, yellow, green, blue, indigo, violet — the colors of the rainbow! We do not usually think of visible light (the visible spectrum) as being an electromagnetic wave, but it is. Figure 2 shows where visible light falls on the electromagnetic spectrum. Figure 2. The electromagnetic spectrum in detail. copyright Engineers use electromagnetic waves in all sorts of different inventions. We cannot see most electromagnetic waves, but you do observe these waves every day when you see visible light. Today we are going to build a fascinating invention so that we can see the different colors that are a part of visible light. Let's get started! Lesson Background & Concepts for Teachers (Return to Contents) A wave is a change (a variation) that travels through a substance (or medium). You can often see the change, such as the increased height of a traveling ocean, but what is important to understand is that the medium itself does not travel with the wave. Ripples in a pond are good examples of waves. If no wind, a pond is smooth until a rock is thrown in and disturbs the water. Then ripples, "disturbances" in the pond, travel to the edges. The medium in this case is the water, through which the ripples travel. The water is not actually moving, but the waves (ripples) are. Waves move in two ways: longitudinally and transversely. Transverse waves oscillate (move back and forth) in a direction perpendicular to their motion. Our pond ripples, for instance, oscillate up and down but move horizontally towards the edge of the pond. Because the ripples oscillate perpendicular to their horizontal motion towards the edge, they can be classified as transverse waves. An electromagnetic wave is a transverse wave that can travel through empty space or a vacuum. Literally, electromagnetic waves are able to travel through "emptiness," unlike sound waves, which need "something" to travel through (for example, water or air). Electromagnetic waves have two parts to them: electric and magnetic. Both of these parts are considered transverse waves. Waves with high frequencies have a lot of energy, and, waves with smaller frequencies have less energy. Most electromagnetic waves are not visible. However, a small section of the spectrum includes waves that we can see — it is called the visible spectrum (see Figure 3). These visible wavelengths allow us to see the colors of the rainbow: red, orange, yellow, green, blue, indigo and violet. We do not usually think of visible light (the visible spectrum) as being an electromagnetic wave, but it is. The electromagnetic spectrum can be considered from another perspective — in nanometers — specifically from 400 nm to 700 nm. Each color in this visual range has a different wavelength. Red has the longest wavelength (700 nm) and violet has the shortest wavelength (400 nm). Green occurs near the middle at about 550 nm. A prism divides light into the wavelengths that make it up. Seen together, color waves make white light. White light is especially dramatic because many different colors of the visual spectrum can combine to make white light. Two "white" light sources can have very different spectral compositions. When white light shines on a prism, the Figure 3. The visual spectrum occurs between 400 nm (violet) and 700 nm colors in white light separate from each (red). other because they refract at different copyright angles depending on their wavelength (see Figure 4). Water droplets in the air refract sunlight to create rainbows. Light can be absorbed, reflected (or diffused) and refracted. Some materials can affect how light bends in more than one way, refracting and reflecting at the same time. Objects made of more than one substance usually have different reflective, refractive and absorptive properties. Light reflects at a predictable angle: the angle of the light that strikes a surface equals the angle of the light that bounces off the surface. Rough surfaces scatter — or diffuse — light, which can cause glare, blur an image or prevent us from seeing an image. Light changes speed and direction — refracts — when it moves from one transparent medium to another. The refractive property of transparent materials can be used to make lenses that focus light (for Figure 4. White light shining through a prism example, cameras, eyeglasses, telescopes). breaks apart into the colors of the visible light spectrum. copyright Since visible light is the part of the electromagnetic spectrum that our eyes can see (remember, we cannot see most electromagnetic waves), our whole world is oriented around it and the colors that are produced through this visible spectrum. Understanding these visible electromagnetic waves has enabled engineers to develop many instruments that can see farther and more clearly than our eyes. That is why we use satellites to look at the Earth, and telescopes to look at the Sky! Vocabulary/Definitions (Return to Contents) electromagnetic wave: visual spectrum: A transverse wave with electric and magnetic parts that travels at 300,000 km/sec. Examples are gamma waves, x-rays, light waves, microwaves, and radio waves. The range of the electromagnetic spectrum — between 400 nm and 700 nm — that our eyes can see. Associated Activities (Return to Contents) Building a Fancy Spectrograph - Students create and decorate their own spectrographs using simple materials and holographic diffraction gratings. A holographic diffraction grating acts like a prism, showing the visual components of light. After building the spectrographs, students observe the spectra of different light sources as homework. The Visual Spectrum - Students make simple spectroscopes (prisms) to look at different light sources. Using the spectroscopes, students see differing spectral distributions of different light sources Lesson Closure (Return to Contents) You all did a great job today of being good listeners and thinking hard about light! We learned that light can be thought of as a wave, just as sound is a wave. We also learned that our eyes can only see some wavelengths of electromagnetic radiation. What do we call the set of wavelengths that our eyes can see ? That's right---the visible spectrum. We also discovered that engineers use many different electromagnetic waves for many different applications. In our next lesson, we are going to learn about rainbows, and continue to follow the adventures of Angie and Harmon. What do you think will happen to them next? Attachments (Return to Contents) Electromagnetic Transparency #1 (doc) Electromagnetic Transparency #1 (pdf) Electromagnetic Transparency #2 (doc) Electromagnetic Transparency #2 (pdf) Assessment (Return to Contents) Pre-Lesson Assessment Discussion Question: Turn on a radio, and tune it to a station. Next turn on a lamp. Ask the students what the two devices (radio and lamp) have in common. (Answer: They both use electromagnetic waves.) Tell students that today we are going to learn about a few different types of electromagnetic waves. Post-Introduction Assessment Fill in the Table: On the left side of the classroom board, list the types of electromagnetic waves. Then work with the students to fill in the right side with ways that engineers use each type of wave. Examples of waves and their uses are: Gamma waves – emitted by nuclear power plants X-rays – used for healthcare Light waves – for seeing visible light Microwaves – for cooking Radio waves – for communication Lesson Summary Assessment What I Learned Today: At lesson end, give students time to think about what they learned. Invite a few students to volunteer something new that they learned through the lesson. (If students do not mention it, remind them that they learned that visible light is an electromagnetic wave and the only electromagnetic wave we can see; also it is only a small portion of the overall spectrum of electromagnetic waves.) Lesson Extension Activities (Return to Contents) Bring in small prisms for students to experiment with and explore how they break light into different wavelengths/colors. Have students create an electromagnetic wave journal of different electromagnetic waves they experience throughout the week (for example, microwaving food, seeing a rainbow, listening to the radio, etc.). Invite an engineer to visit the class and talk about how s/he uses electromagnetic waves in his/her research or work.