An overexposure to UVB radiation can cause sunburn and some forms of skin cancer. In humans, prolonged exposure to solar UV radiation may result in acute and chronic health effects on the skin, eye, and immune system. Moreover, UVC can cause adverse effects that can variously be mutagenic or carcinogenic. The International Agency for Research on Cancer of the World Health Organization has classified all categories and wavelengths of ultraviolet radiation as a Group 1 carcinogen. UVB exposure induces the production of vitamin D in the skin.
The majority of positive health effects are related to this vitamin. It has regulatory roles in calcium metabolism which is vital for normal functioning of the nervous system, as well as for bone growth and maintenance of bone density , immunity, cell proliferation, insulin secretion, and blood pressure.
X-rays are electromagnetic waves with wavelengths in the range of 0. They are shorter in wavelength than UV rays and longer than gamma rays. X-ray photons carry enough energy to ionize atoms and disrupt molecular bonds. This makes it a type of ionizing radiation and thereby harmful to living tissue.
A very high radiation dose over a short amount of time causes radiation sickness, while lower doses can give an increased risk of radiation-induced cancer. In medical imaging this increased cancer risk is generally greatly outweighed by the benefits of the examination. The ionizing capability of X-rays can be utilized in cancer treatment to kill malignant cells using radiation therapy. It is also used for material characterization using X-ray spectroscopy.
X-Ray Spectrum and Applications : X-rays are part of the electromagnetic spectrum, with wavelengths shorter than those of visible light. Different applications use different parts of the X-ray spectrum.
X-rays with photon energies above 5 to 10 keV below 0. Due to their penetrating ability, hard X-rays are widely used to image the inside of objects e. As a result, the term X-ray is metonymically used to refer to a radiographic image produced using this method, in addition to the method itself. Since the wavelength of hard X-rays are similar to the size of atoms, they are also useful for determining crystal structures by X-ray crystallography.
In medical diagnostic applications, the low energy soft X-rays are unwanted, since they are totally absorbed by the body, increasing the radiation dose without contributing to the image.
Hence, a thin metal sheet, often of aluminum, called an X-ray filter, is usually placed over the window of the X-ray tube, absorbing the low energy part in the spectrum. This is called hardening the beam since it shifts the center of the spectrum towards higher energy or harder X-rays. The distinction between X-rays and gamma rays is somewhat arbitrary.
The electromagnetic radiation emitted by X-ray tubes generally has a longer wavelength than the radiation emitted by radioactive nuclei. Historically, therefore, an alternative means of distinguishing between the two types of radiation has been by their origin: X-rays are emitted by electrons outside the nucleus, while gamma rays are emitted by the nucleus.
There is overlap between the wavelength bands of photons emitted by electrons outside the nucleus, and photons emitted by the nucleus.
Like all electromagnetic radiation, the properties of X-rays or gamma rays depend only on their wavelength and polarization. Gamma rays are very high frequency electromagnetic waves usually emitted from radioactive decay with frequencies greater than 10 19 Hz. Identify wavelength range characteristic for gamma rays, noting their biological effects and distinguishing them from gamma rays.
However, this is not a hard and fast definition, but rather only a rule-of-thumb description for natural processes. Gamma rays from radioactive decay are defined as gamma rays no matter what their energy, so that there is no lower limit to gamma energy derived from radioactive decay. Gamma decay commonly produces energies of a few hundred keV, and almost always less than 10 MeV. Gamma rays are ionizing radiation and are thus biologically hazardous.
They are classically produced by the decay from high energy states of atomic nuclei, a process called gamma decay, but are also created by other processes. Paul Villard, a French chemist and physicist, discovered gamma radiation in , while studying radiation emitted from radium during its gamma decay. Natural sources of gamma rays on Earth include gamma decay from naturally occurring radioisotopes such as potassium, and also as a secondary radiation from various atmospheric interactions with cosmic ray particles.
Some rare terrestrial natural sources that produce gamma rays that are not of a nuclear origin, are lightning strikes and terrestrial gamma-ray flashes, which produce high energy emissions from natural high-energy voltages. Gamma rays are produced by a number of astronomical processes in which very high-energy electrons are produced. Such electrons produce secondary gamma rays by the mechanisms of bremsstrahlung, inverse Compton scattering and synchrotron radiation.
Notable artificial sources of gamma rays include fission such as occurs in nuclear reactors, and high energy physics experiments, such as neutral pion decay and nuclear fusion. Gamma rays have characteristics identical to X-rays of the same frequency—they differ only in source. They have many of the same uses as X-rays, including cancer therapy. Gamma radiation from radioactive materials is used in nuclear medicine. The distinction between X-rays and gamma rays has changed in recent decades.
Originally, the electromagnetic radiation emitted by X-ray tubes almost invariably had a longer wavelength than the radiation gamma rays emitted by radioactive nuclei. However, with artificial sources now able to duplicate any electromagnetic radiation that originates in the nucleus, as well as far higher energies, the wavelengths characteristic of radioactive gamma ray sources vs.
Thus, gamma rays are now usually distinguished by their origin: X-rays are emitted by definition by electrons outside the nucleus, while gamma rays are emitted by the nucleus. Exceptions to this convention occur in astronomy, where gamma decay is seen in the afterglow of certain supernovas, but other high energy processes known to involve other than radioactive decay are still classed as sources of gamma radiation. A notable example is extremely powerful bursts of high-energy radiation normally referred to as long duration gamma-ray bursts, which produce gamma rays by a mechanism not compatible with radioactive decay.
These bursts of gamma rays, thought to be due to the collapse of stars called hypernovas, are the most powerful events so far discovered in the cosmos. Bright spots within the galactic plane are pulsars spinning neutron stars with strong magnetic fields , while those above and below the plane are thought to be quasars galaxies with supermassive black holes actively accreting matter. All ionizing radiation causes similar damage at a cellular level, but because rays of alpha particles and beta particles are relatively non-penetrating, external exposure to them causes only localized damage e.
Gamma rays and neutrons are more penetrating, causing diffuse damage throughout the body e. The most biological damaging forms of gamma radiation occur at energies between 3 and 10 MeV. Privacy Policy. Skip to main content. Electromagnetic Waves.
Search for:. The Electromagnetic Spectrum. There is a wide range of subcategories contained within radio including AM and FM radio. Radio waves can be generated by natural sources such as lightning or astronomical phenomena; or by artificial sources such as broadcast radio towers, cell phones, satellites and radar. AM waves have constant frequency, but a varying amplitude.
FM radio waves are also used for commercial radio transmission in the frequency range of 88 to MHz. FM stands for frequency modulation, which produces a wave of constant amplitude but varying frequency. Information is carried by amplitude variation, while the frequency remains constant. FM radio waves : Waves used to carry commercial radio signals between 88 and MHz.
Information is carried by frequency modulation, while the signal amplitude remains constant. Microwaves Microwaves are electromagnetic waves with wavelengths ranging from one meter to one millimeter frequencies between MHz and GHz.
Learning Objectives Distinguish three ranges of the microwave portion of the electromagnetic spectrum. Key Takeaways Key Points The microwave region of the electromagnetic EM spectrum is generally considered to overlap with the highest frequency shortest wavelength radio waves. The microwave portion of the electromagnetic spectrum can be subdivided into three ranges listed below from high to low frequencies: extremely high frequency 30 to GHz , super high frequency 3 to 30 GHz , and ultra-high frequency MHz to 3 GHz.
Microwave sources include artificial devices such as circuits, transmission towers, radar, masers, and microwave ovens, as well as natural sources such as the Sun and the Cosmic Microwave Background. Microwaves can also be produced by atoms and molecules. They are, for example, a component of electromagnetic radiation generated by thermal agitation. Key Terms terahertz radiation : Electromagnetic waves with frequencies around one terahertz.
Learning Objectives Distinguish three ranges of the infrared portion of the spectrum, and describe processes of absorption and emission of infrared light by molecules. Key Takeaways Key Points Infrared light includes most of the thermal radiation emitted by objects near room temperature. This is termed thermography, mainly used in military and industrial applications.
Cable companies have antennae or dishes which receive waves broadcasted from your local TV stations. The signal is then sent through a cable to your house. Why are car antennae about the same size as TV antennae? Cellular phones also use radio waves to transmit information. These waves are much smaller that TV and FM radio waves. Why are antennae on cell phones smaller than antennae on your radio? Radio telescopes are dishes made out of conducting metal that reflect radio waves to a focus point.
We can rearrange this equation to find the wavelength for all three frequencies. These wavelengths are consistent with the spectrum in Figure 1.
The wavelengths are also related to other properties of these electromagnetic waves, as we shall see. The wavelengths found in the preceding example are representative of AM, FM, and cell phones, and account for some of the differences in how they are broadcast and how well they travel.
Thus a very large antenna is needed to efficiently broadcast typical AM radio with its carrier wavelengths on the order of hundreds of meters. One benefit to these long AM wavelengths is that they can go over and around rather large obstacles like buildings and hills , just as ocean waves can go around large rocks. FM and TV are best received when there is a line of sight between the broadcast antenna and receiver, and they are often sent from very tall structures.
FM, TV, and mobile phone antennas themselves are much smaller than those used for AM, but they are elevated to achieve an unobstructed line of sight.
See Figure 6. Figure 6. The actual antennas are small structures on top of the tower—they are placed at great heights to have a clear line of sight over a large broadcast area.
Astronomers and astrophysicists collect signals from outer space using electromagnetic waves. Even everyday gadgets like our car keys having the facility to lock car doors remotely and being able to turn TVs on and off using remotes involve radio-wave frequencies. In order to prevent interference between all these electromagnetic signals, strict regulations are drawn up for different organizations to utilize different radio frequency bands.
One reason why we are sometimes asked to switch off our mobile phones operating in the range of 1. For example, radio waves used in magnetic resonance imaging MRI have frequencies on the order of MHz, although this varies significantly depending on the strength of the magnetic field used and the nuclear type being scanned.
MRI is an important medical imaging and research tool, producing highly detailed two- and three-dimensional images. Radio waves are broadcast, absorbed, and reemitted in a resonance process that is sensitive to the density of nuclei usually protons or hydrogen nuclei. The wavelength of MHz radio waves is 3 m, yet using the sensitivity of the resonant frequency to the magnetic field strength, details smaller than a millimeter can be imaged.
The intensity of the radio waves used in MRI presents little or no hazard to human health. Microwaves are the highest-frequency electromagnetic waves that can be produced by currents in macroscopic circuits and devices. Microwave frequencies range from about 10 9 Hz to the highest practical LC resonance at nearly 10 12 Hz. Microwaves can also be produced by atoms and molecules.
They are, for example, a component of electromagnetic radiation generated by thermal agitation. The thermal motion of atoms and molecules in any object at a temperature above absolute zero causes them to emit and absorb radiation. Figure 7. An image of Sif Mons with lava flows on Venus, based on Magellan synthetic aperture radar data combined with radar altimetry to produce a three-dimensional map of the surface.
The Venusian atmosphere is opaque to visible light, but not to the microwaves that were used to create this image. Since it is possible to carry more information per unit time on high frequencies, microwaves are quite suitable for communications.
Most satellite-transmitted information is carried on microwaves, as are land-based long-distance transmissions. A clear line of sight between transmitter and receiver is needed because of the short wavelengths involved. Radar is a common application of microwaves that was first developed in World War II. By detecting and timing microwave echoes, radar systems can determine the distance to objects as diverse as clouds and aircraft.
A Doppler shift in the radar echo can be used to determine the speed of a car or the intensity of a rainstorm. Sophisticated radar systems are used to map the Earth and other planets, with a resolution limited by wavelength.
See Figure 7. The shorter the wavelength of any probe, the smaller the detail it is possible to observe. How does the ubiquitous microwave oven produce microwaves electronically, and why does food absorb them preferentially? Microwaves at a frequency of 2. The microwaves are then used to induce an alternating electric field in the oven.
Water and some other constituents of food have a slightly negative charge at one end and a slightly positive charge at one end called polar molecules. The range of microwave frequencies is specially selected so that the polar molecules, in trying to keep orienting themselves with the electric field, absorb these energies and increase their temperatures—called dielectric heating.
The energy thereby absorbed results in thermal agitation heating food and not the plate, which does not contain water. Hot spots in the food are related to constructive and destructive interference patterns. Rotating antennas and food turntables help spread out the hot spots. Another use of microwaves for heating is within the human body.
This is used for treating muscular pains, spasms, tendonitis, and rheumatoid arthritis. Microwaves generated by atoms and molecules far away in time and space can be received and detected by electronic circuits. Deep space acts like a blackbody with a 2. The microwave and infrared regions of the electromagnetic spectrum overlap see Figure 1.
Infrared radiation is generally produced by thermal motion and the vibration and rotation of atoms and molecules. Electronic transitions in atoms and molecules can also produce infrared radiation. The range of infrared frequencies extends up to the lower limit of visible light, just below red. Night-vision scopes can detect the infrared emitted by various warm objects, including humans, and convert it to visible light.
We can examine radiant heat transfer from a house by using a camera capable of detecting infrared radiation. Reconnaissance satellites can detect buildings, vehicles, and even individual humans by their infrared emissions, whose power radiation is proportional to the fourth power of the absolute temperature. More mundanely, we use infrared lamps, some of which are called quartz heaters, to preferentially warm us because we absorb infrared better than our surroundings.
About half of the solar energy arriving at the Earth is in the infrared region, with most of the rest in the visible part of the spectrum, and a relatively small amount in the ultraviolet. On average, 50 percent of the incident solar energy is absorbed by the Earth. The relatively constant temperature of the Earth is a result of the energy balance between the incoming solar radiation and the energy radiated from the Earth. Most of the infrared radiation emitted from the Earth is absorbed by CO 2 and H 2 O in the atmosphere and then radiated back to Earth or into outer space.
Some scientists think that the increased concentration of CO 2 and other greenhouse gases in the atmosphere, resulting from increases in fossil fuel burning, has increased global average temperatures. Visible light is the narrow segment of the electromagnetic spectrum to which the normal human eye responds.
Visible light is produced by vibrations and rotations of atoms and molecules, as well as by electronic transitions within atoms and molecules. The receivers or detectors of light largely utilize electronic transitions. We say the atoms and molecules are excited when they absorb and relax when they emit through electronic transitions. Figure 8 shows this part of the spectrum, together with the colors associated with particular pure wavelengths.
We usually refer to visible light as having wavelengths of between nm and nm. The retina of the eye actually responds to the lowest ultraviolet frequencies, but these do not normally reach the retina because they are absorbed by the cornea and lens of the eye. Red light has the lowest frequencies and longest wavelengths, while violet has the highest frequencies and shortest wavelengths.
Blackbody radiation from the Sun peaks in the visible part of the spectrum but is more intense in the red than in the violet, making the Sun yellowish in appearance. Figure 8. A small part of the electromagnetic spectrum that includes its visible components. The divisions between infrared, visible, and ultraviolet are not perfectly distinct, nor are those between the seven rainbow colors. Living things—plants and animals—have evolved to utilize and respond to parts of the electromagnetic spectrum they are embedded in.
Visible light is the most predominant and we enjoy the beauty of nature through visible light. Plants are more selective. Photosynthesis makes use of parts of the visible spectrum to make sugars. During laser vision correction, a brief burst of nm ultraviolet light is projected onto the cornea of a patient.
It makes a spot 0. The energy from the laser light goes toward raising the temperature of the tissue and also toward evaporating it.
Thus we have two amounts of heat to add together. Also, we need to find the mass of corneal tissue involved. We know that. For this case,. The lasers used for this eye surgery are excimer lasers, whose light is well absorbed by biological tissue. They evaporate rather than burn the tissue, and can be used for precision work.
Most lasers used for this type of eye surgery have an average power rating of about one watt. Optics is the study of the behavior of visible light and other forms of electromagnetic waves.
Optics falls into two distinct categories. When electromagnetic radiation, such as visible light, interacts with objects that are large compared with its wavelength, its motion can be represented by straight lines like rays. Ray optics is the study of such situations and includes lenses and mirrors. When electromagnetic radiation interacts with objects about the same size as the wavelength or smaller, its wave nature becomes apparent.
For example, observable detail is limited by the wavelength, and so visible light can never detect individual atoms, because they are so much smaller than its wavelength. Physical or wave optics is the study of such situations and includes all wave characteristics. When you light a match you see largely orange light; when you light a gas stove you see blue light.
Why are the colors different? What other colors are present in these? Ultraviolet is also produced by atomic and molecular motions and electronic transitions. The wavelengths of ultraviolet extend from nm down to about 10 nm at its highest frequencies, which overlap with the lowest X-ray frequencies.
It was recognized as early as by Johann Ritter that the solar spectrum had an invisible component beyond the violet range. It is largely exposure to UV-B that causes skin cancer. Again, treatment is often successful if caught early. All UV radiation can damage collagen fibers, resulting in an acceleration of the aging process of skin and the formation of wrinkles.
Some studies indicate a link between overexposure to the Sun when young and melanoma later in life. The tanning response is a defense mechanism in which the body produces pigments to absorb future exposures in inert skin layers above living cells.
Repeated exposure to UV-B may also lead to the formation of cataracts in the eyes—a cause of blindness among people living in the equatorial belt where medical treatment is limited. However, treatment is easy and successful, as one replaces the lens of the eye with a plastic lens.
Prevention is important. Eye protection from UV is more effective with plastic sunglasses than those made of glass. A major acute effect of extreme UV exposure is the suppression of the immune system, both locally and throughout the body. Low-intensity ultraviolet is used to sterilize haircutting implements, implying that the energy associated with ultraviolet is deposited in a manner different from lower-frequency electromagnetic waves.
Actually this is true for all electromagnetic waves with frequencies greater than visible light. Flash photography is generally not allowed of precious artworks and colored prints because the UV radiation from the flash can cause photo-degradation in the artworks.
Often artworks will have an extra-thick layer of glass in front of them, which is especially designed to absorb UV radiation. However, the layer of ozone O 3 in our upper atmosphere 10 to 50 km above the Earth protects life by absorbing most of the dangerous UV radiation. Unfortunately, today we are observing a depletion in ozone concentrations in the upper atmosphere.
0コメント