Electromagnetic Radiation Electromagnetic Radiation Electromagnetic radiation is a type of energy that is commonly known as light . Generally speaking, we say that light travels in waves, and all electromagnetic radiation travels at the same speed which is about 3.0 * 108 meters per second through a vacuum. We call this the "speed of light"; nothing can move faster than the speed of light. A wavelength is one cycle of a wave, and we measure it as the distance between any two consecutive peaks of a wave. The peak is the highest point of the wave, and the trough is the lowest point of the wave. Frequency So when we talk about light traveling in waves, we can also talk about frequency, or the number of wavelengths that pass a certain point in a given length of time. We usually measure this as the number of wavelength cycles that pass per second. The units for this measurement are Hertz (hz). So, if the wavelength of a light wave is shorter, that means that the frequency will be higher because one cycle can pass in a shorter amount of time. This means that more cycles can pass by the set point in 1 second.

Likewise, a light wave that has a longer wavelength will have a lower frequency because each cycle takes a longer time to complete. This is an example of a shorter wavelength. Like we said earlier, if you were an observer standing on the black line, and you were so quick that you could count the number of wave peaks that passed you in one second, you would find that the number of wave peaks that you counted would be higher than a longer wavelength. This is an example of a longer wavelength. Suppose you put yourself on the line again and you start clocking the number of wave peaks that pass you. Wait a minute, not nearly so many wave peaks have gone by in one second like before with the shorter wavelength. That means that longer wavelengths have a lower frequency. Conclusion: a longer wavelength means a lower frequency, and a shorter wavelength means a higher frequency! How does this relate to the Electromagnetic Spectrum? Like we said before, light can be characterized by its wavelength. For example, the human eye can detect light at wavelengths between 400 to 900 nanometers. That is why we call this part of the electromagnetic spectrum visible light.

Light waves with shorter wavelengths (and higher frequencies) also have more energy, so types of light like gamma rays, X-rays, and ultraviolet light are more energetic than visible light, and infrared, microwaves, and radio waves are less energetic than the light in the visible spectrum. To go back to the electromagnetic spectrum . electromagnetic radiation ELECTROMAGNETIC RADIATION This page is a basic introduction to the electromagnetic spectrum sufficient for chemistry students interested in UV-visible absorption spectroscopy. If you are looking for any sort of explanations suitable for physics courses, then I'm afraid this isn't the right place for you. Light as a wave form Waves Any wave is essentially just a way of shifting energy from one place to another - whether the fairly obvious transfer of energy in waves on the sea or in the much more difficult-to-imagine waves in light. In waves on water, the energy is transferred by the movement of water molecules. But a particular water molecule doesn't travel all the way across the Atlantic - or even all the way across a pond. Depending on the depth of the water, water molecules follow a roughly circular path.

As they move up to the top of the circle, the wave builds to a crest; as they move down again, you get a trough. The energy is transferred by relatively small local movements in the environment. With water waves it is fairly easy to draw diagrams to show this happening with real molecules. With light it is more difficult. The energy in light travels because of local fluctuating changes in electrical and magnetic fields - hence "electromagnetic" radiation. Note: It would be quite wrong to pretend that I am comfortable with this. Having spent quite a lot of time looking at web pages which try to explain electromagnetic radiation (or even water waves), do I feel that I really understand it? To be honest - no! Although there are some excellent diagrams and animations out there, I still feel as if this is a foreign land. On old maps, where people didn't know enough about the region they were drawing, they sometimes gave up and wrote "Here be dragons". For me, physics is definitely "Here be dragons" territory. If you are a chemistry student, you don't need to worry too much about this.

As long as you are prepared to accept diagrams of wave forms, and can understand the relationships between wavelength, frequency and energy (see below), that's all you need. Please don't e-mail to try to explain all this to me. I'm happy to remain ignorant - life is too short to worry about everything! Wavelength, frequency and the speed of light If you draw a beam of light in the form of a wave (without worrying too much about what exactly is causing the wave!), the distance between two crests is called the wavelength of the light. (It could equally well be the distance between two troughs or any other two identical positions on the wave.) You have to picture these wave crests as moving from left to right. If you counted the number of crests passing a particular point per second, you have the frequency of the light. It is measured in what used to be called "cycles per second", but is now called Hertz, Hz. Cycles per second and Hertz mean exactly the same thing. Orange light, for example, has a frequency of about 5 x 1014 Hz (often quoted as 5 x 108 MHz - megahertz).

That means that 5 x 1014 wave peaks pass a given point every second. Light has a constant speed through a given substance. For example, it always travels at a speed of approximately 3 x 108 metres per second in a vacuum. This is actually the speed that all electromagnetic radiation travels - not just visible light. There is a simple relationship between the wavelength and frequency of a particular colour of light and the speed of light: . . . and you can rearrange this to work out the wavelength from a given frequency and vice versa: These relationships mean that if you increase the frequency, you must decrease the wavelength. Compare this diagram with the similar one above. . . . and, of course, the opposite is true. If the wavelength is longer, the frequency is lower. It is really important that you feel comfortable with the relationship between frequency and wavelength. If you are given two figures for the wavelengths of two different colours of light, you need to have an immediate feel for which one has the higher frequency.

For example, if you were told that a particular colour of red light had a wavelength of 650 nm, and a green had a wavelength of 540 nm, it is important for you to know which has the higher frequency. (It's the green - a shorter wavelength means a higher frequency. Don't go on until that feels right!) Note: nm = nanometre = 10-9 metre. The frequency of light and its energy Each particular frequency of light has a particular energy associated with it, given by another simple equation: You can see that the higher the frequency, the higher the energy of the light. So . . . have you got this sorted out? Try it! Light which has wavelengths of around 380 - 435 nm is seen as a sequence of violet colours. Various red colours have wavelengths around 625 - 740 nm. Which has the highest energy? The light with the highest energy will be the one with the highest frequency - that will be the one with the smallest wavelength. In other words, violet light at the 380 nm end of its range.

The Electromagnetic Spectrum red 625 - 740 Don't assume that there is some clear cut-off point between all these colours. In reality, the colours just merge seamlessly into one another - much more seamlessly than in my diagram! Note: You will find that almost every source you look at for this information gives slightly different wavelengths for the different colours. These values (and the names for the colours) come from the HyperPhysics website. I personally think these are much better names than the traditional "violet, indigo, blue, . . ." - but it really doesn't matter! Placing the visible spectrum in the whole electromagnetic spectrum The electromagnetic spectrum doesn't stop with the colours you can see. It is perfectly possible to have wavelengths shorter than violet light or longer than red light. On the spectrum further up the page, I have shown the ultra-violet and the infra-red, but this can be extended even further into x-rays and radio waves, amongst others. The diagram shows the approximate positions of some of these on the spectrum. Once again, don't worry too much about the exact boundaries between the various sorts of electromagnetic radiation - because there are no boundaries. Just as with visible light, one sort of radiation merges into the next.

Just be aware of the general pattern. Also be aware that the energy associated with the various kinds of radiation increases as the frequency increases. Note: As before, don't take this diagram too literally! It is a composite of several diagrams from different sources, nearly all of which give slightly different boundaries between the different named sorts of radiation. You also mustn't think that this is what the spectrum would actually look like if you were to observe it. The problem lies in the way the scales are drawn. Neither the wavelength nor the frequency scales are simple linear scales - the gap between 102 and 104 is not the same as between 10-2 and 10-4, for example (although they are drawn as the same in the diagram). Work it out! One gap is the difference between 100 and 10,000 (in other words 9,900); the other works out at only 0.0099! That means that in some parts, the spectrum should really be very stretched out, and in others very, very compressed.

And because the wavelength and frequency scales are heading in opposite directions, the stretching or compression would be totally different depending on whether you were plotting the spectrum against wavelength or frequency. Does any of this matter for chemistry purposes? No! Think of the last diagram just as a visual way of placing the various types of radiation relative to each other - it is not a picture of what the spectrum actually looks like. Questions to test your understanding If this is the first set of questions you have done, please read the introductory page before you start. You will need to use the BACK BUTTON on your browser to come back here afterwards. What Wavelength Goes With a Color? Contact Us What Wavelength Goes With a Color? Our eyes are sensitive to light which lies in a very small region of the electromagnetic spectrum labeled "visible light". This "visible light" corresponds to a wavelength range of 400 - 700 nanometers (nm) and a color range of violet through red. The human eye is not capable of "seeing" radiation with wavelengths outside the visible spectrum. The visible colors from shortest to longest wavelength are: violet, blue, green, yellow, orange, and red. Ultraviolet radiation has a shorter wavelength than the visible violet light.

Infrared radiation has a longer wavelength than visible red light. The white light is a mixture of the colors of the visible spectrum. Black is a total absence of light. Earth's most important energy source is the Sun. Sunlight consists of the entire electromagnetic spectrum. Learn more: Violet Light The visible violet light has a wavelength of about 400 nm. Within the visible wavelength spectrum, violet and blue wavelengths are scattered more efficiently than other wavelengths. The sky looks blue, not violet, because our eyes are more sensitive to blue light (the sun also emits more energy as blue light than as violet). The visible indigo light has a wavelength of about 445 nm. Blue Light The visible blue light has a wavelength of about 475 nm. Because the blue wavelengths are shorter in the visible spectrum, they are scattered more efficiently by the molecules in the atmosphere. This causes the sky to appear blue during the main part of the day, when blue light is scattered into your eye no matter which direction you look. Green Light The visible green light has a wavelength of about 510 nm. Grass, for example, appears green because all of the colors in the visible part of the spectrum are absorbed into the leaves of the grass except green.

Green is reflected, therefore grass appears green. The visible orange light has a wavelength of about 590 nm. Low-pressure sodium lamps, like those used in some parking lots, emit a orange-ish (wavelength 589 nm) light. Red Light The visible red light has a wavelength of about 650 nm. At sunrise and sunset, the light you see has traveled a longer distance through the atmosphere. A large amount of blue and violet light has been removed as a result of scattering and the longwave colors, such as red and orange, are more readily seen. There are many wavelengths in the electromagnetic spectrum the human eye cannot detect. Energy with wavelengths too short for humans to see Energy with wavelengths too short to see is "more violet than violet". Light with such short wavelengths is called "Ultraviolet" light. The term "ultra-" means higher than. How do we know this light exists? One way is that this kind of light causes sunburns. Our skin is sensitive to this kind of light. If we stay out in this light without sunblock protection, our skin absorbs this energy.

After the energy is absorbed, it can make our skin change color ("tan") or it can break down the cells and cause other damage. Energy with wavelengths too long for humans to see Energy whose wavelength is too long to see is "redder than red". Light with such long wavelengths is called "Infrared" light. The term "Infra-" means "lower than". How do we know this kind of light exists? One way is that we can feel energy with these wavelengths such as when we sit in front of a campfire or when we get close to a stove burner. Scientists like Samuel Pierpont Langley passed light through a prism and discovered that the infrared light the scientists could not see beyond red could make other things hot. Very long wavelengths of infrared light radiate heat to outer space. This radiation is important to the Earth's energy budget. If this energy did not escape to space, the solar energy that the Earth absorbs would continue to heat the Earth. Electromagnetic Waves - different waves, different wavelengths These original EMS pages will be available until May 31, 2011 at which point you'll automatically be redirected to the new pages.

Electromagnetic Waves have different wavelengths When you listen to the radio, watch TV, or cook dinner in a microwave oven, you are using electromagnetic waves. Radio waves, television waves, and microwaves are all types of electromagnetic waves. They differ from each other in wavelength. Wavelength is the distance between one wave crest to the next. Waves in the electromagnetic spectrum vary in size from very long radio waves the size of buildings, to very short gamma-rays smaller than the size of the nucleus of an atom. Did you know that electromagnetic waves can not only be described by their wavelength, but also by their energy and frequency? All three of these things are related to each other mathematically . This means that it is correct to talk about the energy of an X-ray or the wavelength of a microwave or the frequency of a radio wave. The electromagnetic spectrum includes, from longest wavelength to shortest: radio waves, microwaves, infrared, optical, ultraviolet, X-rays, and gamma-rays.

Molecular Expressions Microscopy Primer: Light and Color - Electromagnetic Radiation Movie Gallery The Nature of Electromagnetic Radiation Visible light is a complex phenomenon that is classically explained with a simple model based on propagating rays and wavefronts, a concept first proposed in the late 1600s by Dutch physicist Christiaan Huygens. Electromagnetic radiation, the larger family of wave-like phenomena to which visible light belongs (also known as radiant energy), is the primary vehicle transporting energy through the vast reaches of the universe. The mechanisms by which visible light is emitted or absorbed by substances, and how it predictably reacts under varying conditions as it travels through space and the atmosphere, form the basis of the existence of color in our universe. The term electromagnetic radiation, coined by Sir James Clerk Maxwell, is derived from the characteristic electric and magnetic properties common to all forms of this wave-like energy, as manifested by the generation of both electrical and magnetic oscillating fields as the waves propagate through space.

Visible light represents only a small portion of the entire spectrum of electromagnetic radiation (as categorized in Figure 1), which extends from high-frequency cosmic and gamma rays through X-rays, ultraviolet light, infrared radiation, and microwaves, down to very low frequency long-wavelength radio waves. The link between light, electricity, and magnetism was not immediately obvious to early scientists who were experimenting with the fundamental properties of light and matter. Infrared light, which lies beyond the longer red wavelengths of visible light, was the first "invisible" form of electromagnetic radiation to be discovered. British scientist and astronomer William Herschel was investigating the association between heat and light with a thermometer and a prism when he found that the temperature was highest in the region just beyond the red portion of the visible light spectrum. Herschel suggested that there must be another type of light in this region that is not visible to the naked eye. Ultraviolet radiation, at the other end of the visible spectrum, was discovered by Wilhelm Ritter, who was one of the first scientists to investigate the energy associated with visible light.

By observing the rate at which various colors of light stimulate darkening of paper saturated with a solution of silver nitrate, Ritter discovered that another invisible form of light, beyond the blue end of the spectrum, yielded the fastest rates. Interactive Tutorial Electromagnetic Wave Propagation Explore wave propagation through space with a sinusoidal representation of electromagnetic radiation. Interact with the tutorial to vary the wavelength and the fill factor of electric and magnetic field vectors. Electricity and magnetism were first associated in 1820 when Danish physicist Hans Christian Oersted discovered that electrical current flowing through a wire could produce deflections of a compass needle. Later that same year, French scientist Andr�-Marie Amp�re demonstrated that two wires carrying electrical currents could be made to attract or repel each other, in a fashion similar to that of magnetic poles. During the next few decades, additional investigations following these leads produced an increasing amount of evidence that electricity and magnetism were very closely related to each other. Finally, in 1865, Scottish scientist James Clerk Maxwell expanded his kinetic theory of gases to mathematically explain the links between electricity and magnetism.

Maxwell speculated that the two phenomena were so closely bound that they often acted together as electromagnetism, and discovered that alternating current would produce waves composed of both entities that radiated out into space at the speed of light. From these observations, he concluded that visible light was a form of electromagnetic radiation. An electromagnetic wave travels or propagates in a direction that is oriented at right angles to the vibrations of both the electric (E) and magnetic (B) oscillating field vectors, transporting energy from the radiation source to an undetermined final destination. The two oscillating energy fields are mutually perpendicular (illustrated in Figure 2) and vibrate in phase following the mathematical form of a sine wave. Electric and magnetic field vectors are not only perpendicular to each other, but are also perpendicular to the direction of wave propagation. By convention, and to simplify illustrations, the vectors representing the electric and magnetic oscillating fields of electromagnetic waves are often omitted, although they are understood to still exist.

Whether taking the form of a signal transmitted to a radio from the broadcast station, heat radiating from a fireplace, the dentist's X-rays producing images of teeth, or the visible and ultraviolet light emanating from the sun, the various categories of electromagnetic radiation all share identical and fundamental wave-like properties. Every category of electromagnetic radiation, including visible light, oscillates in a periodic fashion with peaks and valleys (or troughs), and displays a characteristic amplitude, wavelength, and frequency that together define the direction, energy, and intensity of the radiation. The classical schematic diagram of an electromagnetic wave presented in Figure 2 illustrates the sinusoidal nature of oscillating electric and magnetic component vectors as they propagate through space. As a matter of convenience, most illustrations depicting electromagnetic radiation purposely omit the magnetic component, instead representing only the electric field vector as a sine wave in a two-dimensional graphical plot having defined x and y coordinates. By convention, the y component of the sine wave indicates the amplitude of the electric (or magnetic field), while the x component represents time, the distance traveled, or the phase relationship with another sine wave.

A standard measure of all electromagnetic radiation is the magnitude of the wavelength (in a vacuum), which is usually stated in units of nanometers (one-thousandth of a micrometer) for the visible light portion of the spectrum. The wavelength is defined as the distance between two successive peaks (or valleys) of the waveform (see Figure 2). The corresponding frequency of the radiated wave, which is the number of sinusoidal cycles (oscillations or complete wavelengths) that pass a given point per second, is proportional to the reciprocal of the wavelength. Thus, longer wavelengths correspond to lower frequency radiation and shorter wavelengths correspond to higher frequency radiation. Frequency is usually expressed in quantities of hertz (Hz) or cycles per second (cps). The hertz was designated as a standard unit of electromagnetic radiation frequency in recognition of the work of German physicist Heinrich Hertz, who succeeded in generating and performing experiments with electromagnetic waves in 1887, eight years after the death of Maxwell. Hertz produced, detected, and even measured the wavelength (approximately one meter) of radiation that is now classified in the radiofrequency range.

David Hughes, a London-born scientist who was a music professor in his early career, may have actually been the first investigator to succeed in the transmission of radio waves (in 1879), but after failing to convince the Royal Society, he decided not to publish his work, and it wasn't recognized until many years later. Interactive Tutorial Basic Electromagnetic Wave Properties Examine how the frequency, energy, and wavelength of an electromagnetic wave are related, and how changing one automatically produces a corresponding change in the other two (and the color of visible light). The different wavelengths and frequencies comprising the various forms of electromagnetic radiation are fundamentally similar in that they all travel at the same speed�about 186,000 miles per second (or approximately 300,000 kilometers per second), a velocity commonly known as the speed of light (and designated by the symbol c). Electromagnetic radiation (including visible light) travels 149 million kilometers (93 million miles) from the sun to Earth in about 8 minutes. In contrast, an automobile speeding at 100 kilometers per hour (60 miles per hour) would require 177 years to make the same one-way trip.

In only one second, light can circumnavigate the Earth seven times. The wavelength of light, and all other forms of electromagnetic radiation, is related to the frequency by a relatively simple equation: n = c/l where c is the speed of light (in meters per second), n is the frequency of the light in hertz (Hz), and l is the wavelength of the light measured in meters. From this relationship one can conclude that the wavelength of light is inversely proportional to frequency. An increase in frequency produces a proportional decrease in the wavelength of light, with a corresponding increase in the energy of photons that comprise the light. Upon entering a new medium (such as glass or water from air), the speed and wavelength of light is reduced, although the frequency remains unaltered. Under normal circumstances, when traveling through a uniform medium, such as air or a vacuum, light propagates in straight lines until interaction with another medium or material induces a path change, through refraction (bending) or reflection. The intensity may be also reduced as a result of absorption by the medium. If the light waves pass through a narrow slit or aperture (hole), then they can be diffracted or dispersed (scattered) to form a characteristic diffraction pattern.

In accordance with the well-known inverse square law, the intensity (or irradiance) of electromagnetic radiation is inversely proportional to the square of the distance traveled. Thus, after light has traveled twice a given distance, the intensity drops by a factor of four. Visible light displays classical wave-like properties, but it also exhibits properties reminiscent of particles, which are manifested through entities that possess energy and momentum (but no mass), and are referred to as photons. The atom is the source of all forms of electromagnetic radiation, whether visible or invisible. Higher-energy forms of radiation, such as gamma waves and X-rays, are produced by events that occur to disrupt the nuclear stability of the atom. Radiation having lower energy, such as ultraviolet, visible, and infrared light, as well as radio and microwaves, originate from the electron clouds that surround the nucleus or the interaction of one atom with another. These forms of radiation occur due to fact that electrons moving in orbits around the nucleus of an atom are arranged in different energy levels within their probability distribution functions. Many of the electrons can absorb additional energy from external sources of electromagnetic radiation (see Figure 3), which results in their promotion to an inherently unstable higher energy level.

Eventually, the "excited" electron loses the extra energy by emitting electromagnetic radiation of lower energy and, in doing so, falls back into its original and stable energy level. The energy of the emitted radiation equals the energy that was originally absorbed by the electron minus other small quantities of energy lost through a number of secondary processes. Electromagnetic radiation energy levels can vary to a significant degree depending upon the energy of source electrons or nuclei. For example, radio waves possess significantly less energy than do microwaves, infrared rays, or visible light, and all of these waves contain far less energy than ultraviolet light, X-rays, and gamma waves. As a rule, higher electromagnetic radiation energies are associated with shorter wavelengths than similar forms of radiation having lower energy. The relationship between the energy of an electromagnetic wave and its frequency is expressed by the equation: E = hn = hc/l where E is the energy in kilojoules per mole, h is Planck's constant, and the other variables are defined as discussed previously. Based on this equation, the energy of an electromagnetic wave is directly proportional to its frequency and inversely proportional to the wavelength. Thus, as frequency increases (with a corresponding decrease in wavelength), the electromagnetic wave energy increases, and vice versa.

Selected characteristics of the different types of electromagnetic radiation, as defined by their wavelength, frequency, and energy levels, will be reviewed individually in the following paragraphs. Even though electromagnetic radiation is customarily described by the wavelength and frequency of the waveforms, other characteristic properties are important when considering how waves propagate through space. Presented in Figure 4 are various waveforms representing common states that are utilized to describe the degree of uniformity of electromagnetic radiation. Because visible light is the most commonly discussed form of radiation, the examples illustrated in Figure 4 are representative of wavelengths in this spectral region. For example, monochromatic light consists of waves all having the same wavelength and frequency, or macroscopically, the same color in visible light. In contrast, polychromatic visible light usually appears as white due to contributions from the mixture of all or most wavelengths in the spectrum ranging between 400 and 700 nanometers. When light is non-polarized (Figure 4), the electric field vectors vibrate in all planes lying perpendicular to the direction of propagation.

Light that has been reflected from a smooth surface at a critical angle, or passed through polarizing filters, assumes a plane-polarized orientation with all of the electric vectors vibrating in a single plane perpendicular to the direction of propagation. Light from the sun, and a majority of the common incandescent and fluorescent visible light sources, is non-polarized, while light seen through polarizing lenses of custom sunglasses is polarized in the vertical direction. In some instances, light can be elliptically or circularly polarized when it passes through materials that have more than one refractive index (birefringent or doubly refracting substances). Most artificial and natural light sources emit non-coherent light that displays a variety of phase relationships among the wavelengths present in the spectrum (Figure 4). In this case, the peaks and valleys of the vibrational states in individual waves do not coincide in either space or time. Coherent light is composed of wavelengths that are in phase with each other, and behaves in a very different manner than non-coherent light with respect to the optical properties and interaction with matter.

Wavefronts produced by coherent light have electric and magnetic vector vibrations that oscillate in phase, have low divergence angles, and are usually composed of monochromatic light or wavelengths that have a narrow distribution. Lasers are a common source of coherent light. Light waves that have coaxial, relatively non-diverging paths as they travel through space are termed collimated. This organized form of light does not spread or converge to a significant degree over comparatively long distances. Collimated light forms a very tight beam, but does not necessarily have a narrow band of wavelengths (nor must it be monochromatic), a common phase relationship, or a defined state of polarization. Wavefronts of collimated light are planar and perpendicular to the axis of propagation. In contrast, divergent or non-collimated light spreads to varying degrees while traveling through space, and must be passed through a lens or aperture in order to be collimated or focused. Gamma rays - High-energy radiation that possesses the highest frequency (and shortest wavelengths), gamma rays are emitted as the result of transitions within the atomic nucleus, including nuclei of certain radioactive materials (natural and artificial). Gamma waves also originate from nuclear explosions and a variety of other sources in outer space.

These powerful rays possess tremendous penetrating ability and have been reported to be able to pass through three meters of concrete! Individual gamma-ray photons contain so much energy that they are easily detected, but the extremely small wavelength limits the experimental observation of any wavelike properties. Gamma rays originating from the hottest regions of the universe, including supernova explosions, neutron stars, pulsars, and black holes, travel through vast distances in space to reach the Earth. This high-energy form of radiation has wavelengths less than one-hundredth of a nanometer (10 picometers), photon energies greater than 500 kiloelectron-volts (keV), and frequencies exceeding 30 exahertz (EHz). Exposure to gamma rays can induce mutations, chromosome aberrations, and even cell death, as is often observed in some forms of radiation poisoning. However, by controlling the emission of gamma rays, radiologists can re-direct the high energy levels to combat disease and help cure some forms of cancer. Gamma ray astronomy is a relatively new science that collects these high-energy waves in order to produce images of the universe, as illustrated in Figure 5.

This technique affords scientists opportunities to observe distant celestial phenomena in the search for new physical concepts, and to test theories that cannot be challenged by experiments performed here on the Earth. X-rays - Electromagnetic radiation having a frequency just above the ultraviolet (but below the gamma) range is classified as X-rays, and is energetic enough to pass easily through many materials, including the soft tissues of animals. The high penetration depths of these powerful waves, coupled with their ability to expose photographic emulsions, has led to the extensive use of X-rays in medicine to investigate textures in the human body, and in some cases, as a therapeutic or surgical tool. In the same manner as higher-energy gamma rays, uncontrolled exposure to X-rays can lead to mutations, chromosome aberrations, and other forms of cell damage. Traditional radiographic imaging methods essentially produce nothing more than shadow castings of dense material, rather than detailed images. Recent advances in X-ray focusing technique using mirror optics, however, has led to significantly more detailed imagery from a variety of objects utilizing X-ray telescopes, X-ray microscopes, and interferometers.

Hot gases in outer space emit a powerful spectrum of X-rays, which are utilized by astronomers to gain information about the origin and characteristics of interstellar regions of the universe. Many extremely hot celestial objects, including the sun, black holes, and pulsars, emit primarily in the X-ray region of the spectrum and are the subjects of astronomical X-ray investigations. The frequency spectrum of X-rays spans a very large range with the shortest wavelengths approaching the diameter of an atom. However, the entire X-ray spectral region traverses the length scale between approximately 10 nanometers and 10 picometers. This wavelength range makes X-ray radiation an important tool to geologists and chemists for characterizing the structure and properties of crystalline materials, which have periodic structural features on a length scale comparable to the X-ray wavelengths. Ultraviolet Light - Often abbreviated (uv), ultraviolet radiation propagates at frequencies just above those of violet in the visible light spectrum. Although the low-energy end of this spectral region is adjacent to visible light, ultraviolet rays at the upper end of their frequency range have enough energy to kill living cells and produce significant tissue damage.

The sun is a constant source of ultraviolet radiation, but the atmosphere of the Earth (primarily ozone molecules) effectively blocks a majority of the shorter wavelengths of this potentially lethal radiation stream, thus affording a suitable living environment for plants and animals. Photon energies in the ultraviolet are sufficient to ionize the atoms from a number of gas molecules in the atmosphere, and this is the process by which the ionosphere is created and sustained. Although small doses of this relatively high-energy light can promote the production of vitamin D in the body, and cause minimal tanning of the skin, too much ultraviolet radiation can lead to serious sunburn, permanent retinal damage, and the promotion of skin cancer. Ultraviolet light is utilized extensively in scientific instruments to probe the properties of various chemical and biological systems, and it is also important in astronomical observations of the solar system, galaxy, and other parts of the universe. Stars and other hot celestial objects are strong emitters of ultraviolet radiation. The ultraviolet wavelength spectrum ranges from about 10 to approximately 400 nanometers, with photon energies ranging between 3.2 and 100 electron-volts (eV).

This category of radiation has applications in water and food treatment as an anti-microbial agent, as a photocatalyst for caged compounds, and is utilized to harden casts in medical treatments. The germicidal activity of ultraviolet light occurs at wavelengths less than approximately 290 nanometers. A market for blocking and filtering compounds employed in skin lotions, sunglasses, and window tints aims at controlling exposure to ultraviolet light from the sun. Some insects (notably honeybees) and birds have sufficient visual sensitivity in the ultraviolet region to respond to longer wavelengths, and may rely upon this capability in navigation. Humans are limited in their sensitivity to ultraviolet radiation due to absorption by the cornea of shorter wavelengths, and by strong absorption in the eye lens at wavelengths longer than 300 nanometers. Visible light - The rainbow of colors associated with the visible light spectrum represents only about 2.5 percent of the entire electromagnetic spectrum, and includes photons with energies between approximately 1.6 to 3.2 electron-volts. Color is not a property of the light itself, but the perception of color occurs through the combined response of the human eye-nerve-brain sensing system.

The visible region of the electromagnetic spectrum lies within a narrow frequency band, from approximately 384 to 769 terahertz (THz) and is perceived as colors ranging from deep red (wavelength of 780 nanometers) to deep violet (400 nanometers). The low-energy, long-wavelength red colors (622-780 nanometers) are followed in sequence by orange (597-622 nanometers), yellow (577-597 nanometers), green (492-577 nanometers), blue (455-492 nanometers), and finally, relatively high-energy, short-wavelength violet (455 nanometers and below). An easy method to remember the order (in increasing frequency) of the colors in the visible light spectrum is with the mnemonic acronym ROY G BIV (Red, Orange, Yellow, Green, Blue, Indigo, Violet,), as taught to millions of school children for nearly a century (although indigo is no longer considered a pertinent color by some scientists). Division of the visible light spectrum into color regions based on physical properties is straightforward, but the manner in which color is sensed is not as obvious.

Perception of color results from subjective responses of the human sensing system to the various frequency regions of the visible spectrum, and a variety of different combinations of light frequencies can produce the same visual response of "seeing" a specific color. Humans may perceive the color green, for example, in response to a combination of light of several colors, none of which are necessarily composed of "green" wavelengths. Visible light is the basis for all life on Earth, and is captured by primary producers or autotrophs, such as green plants. These fundamental members of the biological food chain harness sunlight as the source of energy for manufacturing their own food and biochemical building blocks. In return, autotrophs release oxygen, upon which all animals depend, as a by-product. In 1672, Sir Isaac Newton studied the interaction of visible light with a glass prism and first recognized that white light is actually a mixture of different colors representing the entire visible light spectrum. White light originates from a variety of natural and artificial incandescent sources, including the sun, chemical reactions (such as fire), and incandescent tungsten filaments. The broad emission spectrum from sources of this type is referred to as thermal radiation.

Other sources of visible light, such as gas discharge tubes, are capable of emitting light in narrow, well-defined frequency ranges (representing a single color) that depend upon specific energy level transitions in the source material atoms. Strong perception of individual colors also results from specific absorption, reflection, or transmission characteristics of materials and objects that are illuminated with white light. The visible-ultraviolet light absorption spectrum of a common synthetic dye, Iris Blue B, is illustrated in Figure 6. Solutions of this brilliantly colored organic molecule absorb light in both the visible and ultraviolet regions of the spectrum, and appear to most humans as a rich, medium blue color. Infrared Radiation - Often abbreviated IR, the large band of infrared wavelengths extends from the far-red portion of the visible light spectrum (around 700-780 nanometers) to about one millimeter in wavelength. With photon energies ranging from approximately l.2 millielectron-volts to slightly less than 1.7 electron-volts, infrared waves have corresponding frequencies between 300 gigahertz (GHz) and approximately 400 terahertz (THz). This type of radiation is associated with the thermal region where visible light is not necessarily detectable or even present.

For example, the human body does not emit visible light, but it does emit weak infrared radiation, which is felt and can be recorded as heat. The emission spectrum begins at about 3000 nanometers and ranges beyond the far infrared, peaking at approximately 10000 nanometers. Molecules of all objects that exist above the temperature of absolute zero (-273 degrees Celsius) emit infrared rays, and the amount of emission generally increases with temperature. Approximately half of the sun's electromagnetic energy is emitted in the infrared region, and household items such as heaters and lamps also produce large quantities. Incandescent tungsten-filament lamps are rather inefficient producers of light, actually emitting more infrared than visible waves. Common tools that rely on detection of infrared radiation are night vision scopes, electronic detectors, sensors in satellites and airplanes, and astronomical instrumentation. So-called heat-seeking missiles used by the military are guided by infrared detectors. In outer space, infrared wavelengths of radiation map the celestial dust between stars, as evidenced by the large dark patches visible from Earth when viewing the Milky Way Galaxy. In the household, infrared radiation plays a familiar role in heating and drying clothes, as well as allowing the remote control operation of garage doors and home entertainment components.

Infrared photography takes advantage of the near-infrared spectrum to record images on specialized film useful in forensics, remote sensing (such as aerial crop and forest surveys), painting restorations, satellite imaging, and military surveillance applications. Curiously, infrared photographs of sunglasses and other optical surfaces coated with ultraviolet and visible light-blocking agents appear transparent, and reveal the eyes behind seemingly opaque lenses. Infrared photographic film will not record thermal radiation (heat) distribution because it is not sufficiently sensitive to long-wavelength radiation (far-infrared). Presented in Figure 7 are several infrared sensor-generated satellite images of two American cities and Mount Vesuvius, in Italy. Microwaves - Currently the basis of a widespread technology utilized in millions of households for heating food, microwave spectral wavelengths range from approximately one millimeter to thirty centimeters (or about one foot). The appeal of utilizing microwaves in food preparation results from the fortuitous circumstance that water molecules present in most foods have a rotational resonance frequency within the microwave range. At the frequency of 2.45 gigahertz (12.2 centimeter wavelength), water molecules efficiently absorb microwave energy and subsequently dissipate radiation as heat (infrared).

If containers composed of materials that do not contain water are utilized to hold food in the microwave oven, they will tend to remain cool, adding a significant additional convenience to microwave cooking. Interactive Tutorial Tuning a Radio Wave Receiver Discover how a variable capacitor is coupled to a simple antenna transformer circuit to tune specific wavelengths in a broadband radiofrequency spectrum. Microwaves constitute the highest frequency radio waves, and are emitted by the Earth, buildings, cars, airplanes, and other large objects. In addition, low-level microwave radiation permeates space, where it is speculated to have been released by the Big Bang during creation of the universe. Higher frequency microwaves are the basis for RADAR, an acronym that stands for RAdio Detecting And Ranging, a transmission and reception technique used in tracking large objects and calculating their speed and distance. Astronomers utilize extraterrestrial microwave radiation to study the Milky Way and other nearby galaxies. A significant amount of astronomical information has been derived from studying a specific emission wavelength (21-centimeters or 1420-megahertz) of uncharged hydrogen atoms, which are widely distributed throughout space.

Microwaves are also employed for transporting information from Earth to orbiting satellites in vast communications networks, for relaying information from ground-based stations over long distances, and in terrain mapping. Surprisingly, some of the first electromagnetic experiments conducted by Heinrich Hertz, Jagadis Chandra Bose, and Guglielmo Marconi (the father of modern radio), were carried out using radiation in or near the microwave region. Early military applications capitalized on the narrow beamwidth and increased modulation bandwidth allowed by focusable microwaves, which were hard to intercept and contained relatively large amounts of information. There is some controversy in the scientific community over the potential health risks of cancer and thermal tissue damage associated with continual and cumulative microwave radiation exposure from cellular telephone towers, leaking microwave ovens, and the act of placing mobile telephones close to the brain during use. Radio Waves - The expansive radiofrequency portion of the electromagnetic spectrum includes wavelengths from about 30 centimeters to thousands of kilometers. Radiation in this range contains very little energy, and the upper frequency limit (about 1 gigahertz) occurs at the end of the band where radio and television broadcasting is confined.

At such low frequencies, the photon (granular) character of the radiation is not apparent, and the waves appear to transfer energy in a smooth, continuous fashion. There is no theoretical upper limit to the wavelength of radiofrequency radiation. The low-frequency (60 hertz) alternating current carried by power lines, as an example, has a wavelength of about five million meters (or approximately 3,000 miles). Radio waves used for communication are modulated in one of two transmission specifications: amplitude modulated (AM) waves that vary in the amplitude of the wavelengths, and frequency modulated (FM; see Figure 8) waves that vary in wavelength frequency. Radio waves play important roles in industry, communications, medicine, and magnetic resonance imaging (MRI). The sound and video portion of television is transported through the atmosphere by shorter radio waves having wavelengths less than a meter, which are modulated for broadcast much like FM radio. Radio waves are also produced by stars in distant galaxies, and can be detected by astronomers using specialized radiotelescopes. Long waves, several million miles in length, have been detected radiating toward the Earth from deep in space.

Because the signals are so weak, radiotelescopes are often banded together in parallel arrays containing large numbers of enormous antenna-based receivers. The nature of the relationship between the frequency (the number of oscillations per unit time) and wavelength (the length of each oscillation) of light becomes apparent when studying the broad range of the electromagnetic radiation spectrum. Very high-frequency electromagnetic radiation, such as gamma rays, X-rays, and ultraviolet light, comprises very short wavelengths and a significant amount of energy. On the other hand, lower frequency radiation, including visible, infrared, microwave, and radio waves, has correspondingly longer wavelengths with lower energies. Although the electromagnetic spectrum is commonly described as traversing about 24 orders of magnitude in frequency and wavelength, there are no intrinsic upper or lower boundaries to the wavelengths and frequencies of this continuous distribution of radiation. Contributing Authors Mortimer Abramowitz - Olympus America, Inc., Two Corporate Center Drive., Melville, New York, 11747. Thomas J. Fellers and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.

Electromagnetic Spectrum - Introduction Electromagnetic Spectrum - Introduction Basic The 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). (Credit: NASA's Imagine the Universe) 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. 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, or frequency . 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. (Credit: NASA's Imagine the Universe) 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 both angstroms (0.00000001 cm, or 10-8 cm ) and nanometers (0.0000001 cm, or 10-7 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. The Electromagnetic and Visible Spectra Light Waves and Color - Lesson 2 - Color and Vision The Electromagnetic and Visible Spectra The Electromagnetic and Visible Spectra Blue Skies and Red Sunsets As discussed in Unit 10 of The Physics Classroom Tutorial , electromagnetic waves are waves that are capable of traveling through a vacuum. Unlike mechanical waves that require a medium in order to transport their energy, electromagnetic waves are capable of transporting energy through the vacuum of outer space. Electromagnetic waves are produced by a vibrating electric charge and as such, they consist of both an electric and a magnetic component. The precise nature of such electromagnetic waves is not discussed in The Physics Classroom Tutorial.

Nonetheless, there are a variety of statements that can be made about such waves. Electromagnetic waves exist with an enormous range of frequencies. This continuous range of frequencies is known as the electromagnetic spectrum. The entire range of the spectrum is often broken into specific regions. The subdividing of the entire spectrum into smaller spectra is done mostly on the basis of how each region of electromagnetic waves interacts with matter. The diagram below depicts the electromagnetic spectrum and its various regions. The longer wavelength, lower frequency regions are located on the far left of the spectrum and the shorter wavelength, higher frequency regions are on the far right. Two very narrow regions within the spectrum are the visible light region and the X-ray region. You are undoubtedly familiar with some of the other regions of the electromagnetic spectrum. Visible Light Spectrum The focus of Lesson 2 will be upon the visible light region - the very narrow band of wavelengths located to the right of the infrared region and to the left of the ultraviolet region. Though electromagnetic waves exist in a vast range of wavelengths, our eyes are sensitive to only a very narrow band. Since this narrow band of wavelengths is the means by which humans see, we refer to it as the visible light spectrum.

Normally when we use the term "light," we are referring to a type of electromagnetic wave that stimulates the retina of our eyes. In this sense, we are referring to visible light, a small spectrum from the enormous range of frequencies of electromagnetic radiation. This visible light region consists of a spectrum of wavelengths that range from approximately 700 nanometers (abbreviated nm) to approximately 400 nm. Expressed in more familiar units, the range of wavelengths extends from 7 x 10-7 meter to 4 x 10-7 meter. This narrow band of visible light is affectionately known as ROYGBIV. Each individual wavelength within the spectrum of visible light wavelengths is representative of a particular color. That is, when light of that particular wavelength strikes the retina of our eye, we perceive that specific color sensation. Isaac Newton showed that light shining through a prism will be separated into its different wavelengths and will thus show the various colors that visible light is comprised of. The separation of visible light into its different colors is known as dispersion. Each color is characteristic of a distinct wavelength; and different wavelengths of light waves will bend varying amounts upon passage through a prism. For these reasons, visible light is dispersed upon passage through a prism.

Dispersion of visible light produces the colors red (R), orange (O), yellow (Y), green (G), blue (B), and violet (V). It is because of this that visible light is sometimes referred to as ROY G. BIV. (Incidentally, the indigo is not actually observed in the spectrum but is traditionally added to the list so that there is a vowel in Roy's last name.) The red wavelengths of light are the longer wavelengths and the violet wavelengths of light are the shorter wavelengths. Between red and violet, there is a continuous range or spectrum of wavelengths. The visible light spectrum is shown in the diagram below. When all the wavelengths of the visible light spectrum strike your eye at the same time, white is perceived. The sensation of white is not the result of a single color of light. Rather, the sensation of white is the result of a mixture of two or more colors of light. Thus, visible light - the mix of ROYGBIV - is sometimes referred to as white light. Technically speaking, white is not a color at all - at least not in the sense that there is a light wave with a wavelength that is characteristic of white.

Rather, white is the combination of all the colors of the visible light spectrum. If all the wavelengths of the visible light spectrum give the appearance of white, then none of the wavelengths would lead to the appearance of black. Once more, black is not actually a color. Technically speaking, black is merely the absence of the wavelengths of the visible light spectrum. So when you are in a room with no lights and everything around you appears black, it means that there are no wavelengths of visible light striking your eye as you sight at the surroundings. Investigate! The widget below matches the wavelength of light (in nanometers) to a particular color of light. Explore by entering various values between 400 nanometers and 700 nanometers. Values outside this range are not visible and therefore not associated with human-perceived color. Visible Light, Wavelength of Visible Light | Physics@TutorVista.com Back to Top Light is a form of electromagnetic radiation. Human eye has the capability to detect or sense some part of the complete electromagnetic spectrum. The portion of the electromagnetic spectrum which is sensed by our human eye having wavelength in the range between 380nm and 750nm is called Visible light.

Visible Light travels in straight line and the speed of light in vacuum is equal to c = 2.99792458 × 108 m s–1. This is approximately taken as 3 × 108 m s–1 Wavelength of Visible Light Back to Top Wavelength of visible is defined as the distance between the two consecutive crests or between two consecutive troughs. Wavelength of the Visible Light Ranges from 380nm to 750 nm. In the electromagnetic spectrum, Infrared rays has higher wavelength than the visible rays and the ultraviolet rays has smaller wavelength as compared to the visible light. Also we have seen that the visible light contains different types of colors when the light is made to pass through the prism. Colors are produced based on their wavelength. Long Wavelength Visible Light is the Red visible light. The wavelength of the Red visible light ranges from the 625 nm to the 750 nm. The Smallest Wavelength Visible Light is the Violet visible light. The violet visible light has wavelength which ranges from 380 nm to 435 nm.

Frequency of Visible Light is defined as the number of crests which passes through a particular point in a second. It is represented in hertz. Frequency of waves is inversely proportional to their wavelength, which means that higher the wavelength, lower is the frequency and vice versa. The frequency range of the visible light is between 400 to 790 THz. Back to Top Different types of radiations are present In the electromagnetic spectrum. Each type of rays has their spectrum or range of frequencies in the electromagnetic spectrum. In other words we can say that in the complete electromagnetic spectrum, the portion of the electromagnetic spectrum which can be detected by the human eye is termed as the visible light spectrum. Back to Top Light shows both types of properties, particle and wave nature. As a wave visible light shows most of the properties which are shown by waves like reflection, refraction, diffraction, absorption etc. Visible light always travels in the form of straight line. Most important Visible Light Uses is that it makes us to see the different objects or substances. It helps in our day today life. It helps in driving etc. Used by the green plants for photosynthesis. Then it is also used for photoelectric effect to produce current or electricity.

Back to Top As mentioned earlier, a lens is an optical device. It is formed by combination of two curved surfaces, mostly spherical surfaces with a common axis. It allows light and because of the curvatures and of the material of the lens it also gets refracted. Lenses are made of glass or transparent polycarbonate or transparent plastic materials. For the purpose of safety, polycarbonate materials are preferred for making lenses.

Question: What is the name for radiations of a wavelength shorter than, and immediately next to, the visible spectrum?
Answer: Ultra violet