Gamma rays were first observed by the to detect defects in casts, molds, and metal French chemist Paul Villard (1860-1934) sheets. It can also be used as a thickness in 1900 when he was investigating gauge in metal-rolling operations, sheet radiation from the chemical element making, floor tile manufacturing, and radium. The New Zealand-born British asphalt roofing. In agriculture, mutations physicist Ernest Rutherford (1871-1937) in plants and animals can be induced by proposed the name "gamma rays" a few gamma radiation. Some of the beneficial years later. Like with X-rays, scientists mutants are new varieties with better took a long time to determine the exact quality. Gamma rays can also be used in nature of gamma rays because gamma preserving food and sterilizing materials. rays are absorbed in the atmosphere. Thus, scientists can only study them by Effects of Electromagnetic using satellites in space. Gamma rays are used in the treat- Waves on Living Things and ualizing the internal n body. ment of certain diseases such as cancer. the Environment However, the use of gamma rays must be employed carefully and precisely because Because the whole range of energies radiation can damage both normal and in the electromagnetic spectrum interacts cancer cells. Moreover, people that are with Earth and all of its inhabitants, it the shortest working in industries that use gamma is highly significant that humans study st frequencies. rays are required to wear protective suits their effects and impacts on living things for maximum protection against radiation. and the environment. etrating power In industries, gamma radiation is utilized Every day, people are exposed to electromagnetic radiation from various natural and artificial sources. Electromagnetic radiation can be broadly categorized into ionizing and non-ionizing radiation. Ionizing radiation has enough energy to ionize or remove an electron from an atom, which can change the chemical composition of a material. On the other hand, non-ionizing radiation carries less energy but can excite molecules and atoms to vibrate fast. Gamma rays, X-rays, and UV light are considered ionizing radiation; whereas, visible light, IR, microwaves, and radio waves are non- ionizing radiation. Ionizing radiation comes from natural and artificial sources. Radioactive materials such as uranium, thorium, actinium, and potassium-40 are natural Fig. 6.18 Protective suits must be worn when sources of ionizing radiation as they during radioactive handling potentially radioactive materials. can be naturally found in food, air, and as nuclear ch 151long wavelengths Infrared Radiation spectrum. It is emitted by molecules that are colliding with hot gases or solids. The range from 1 to In 1800, the British-German collisions make the molecules vibrate iscovered in 1888 astronomer Sir William Herschel (1738- and emit electromagnetic radiation at monstrated their 1822) studied the differences in the higher frequencies that range from about apparatus that temperature among the colors of the 3.0x10ll to 4.0x10#4 Hz. microwaves in the visible spectrum. In his experiment, he IR is also referred to as heat rays. used a glass prism to separate sunlight Water molecules are present in most be used for into its component colors. He placed a materials, and they readily absorb IR. thermometer within each color, with The absorption of IR causes the random es such as in one extra thermometer beyond the red thermal motion of the water molecules to y systems, two- end of the spectrum. The results of his increase, which causes the materials and tems, and public experiment showed that the thermometer their surroundings to heat up. 6.9). Two-way that was placed beyond the light recorded IR is used in missile guidance, long- are also used the highest temperature. From this, he distance photography, invisible signaling dar devices, and discovered infrared radiation (IR). in burglar alarms, and medical treatment, aves can also be IR is adjacent to the low-frequency, among others. ng (fig. 6.10). The long-wavelength end of the visible vens has reduced 34.8.C cooking time as ctric ovens. 32 2 -26.7 IL21 20.6 34.9" Photograph courtesy of NASA/SPL-Caltech re used to broadcast 28.7 ns, which are usually purposes. 121 20.6 Fig. 6.11 Thermal imaging is the process of detecting the infrared radiation an object emits using an infrared camera, and then converting the received information into visible images that illustrate the distribution of temperature differences in the object. This technology is commonly used to improve the visibility of objects in dark surroundings.Furthermore, the black lights that are used for entertainment emit radiation Gamma rays w mostly in the UV range of the spectrum. White clothes and fluorescent-colored French chemist Pa items glow in the dark when under UV in 1900 when light. The process in which a substance radiation from radium. The New absorbs UV radiation and emits physicist Ernest visible radiation is called fluorescence. proposed the nan For example, the mercury vapor in a years later. Like fluorescent lamp emits UV radiation after took a long time electrical excitation. The white material nature of gamma that is used to coat the inside of the lamp rays are absorb tube absorbs the UV radiation and emits Thus, scientists visible light. using satellites in Gamma ray X-rays Fig. 6.16 X-rays are used in visualizing the ment of certain structures of the human body. However, the use employed carefull X-rays have short wavelengths radiation can da with frequencies that range from about Gamma Rays cancer cells. Mo 3.0x1016 to 3.0x1019 Hz. They are working in indu produced when high-speed electrons are Gamma rays have the shore rays are required abruptly stopped by a hard metal target. wavelengths and the highest frequens for maximum pro When the electrons hit the metal, their They also have high penetrating p In industries, ga speed decreases tremendously. The (fig. 6.17). kinetic energy of the electrons is then transformed into electromagnetic energy. X-rays were discovered accidentally by the German physicist Wilhelm Roentgen (1845-1923) in 1895. During one of his experiments, he noted that a piece of fluorescent paper was illuminated by electrical rays from a cathode-ray tube. Considering the unknown nature of such rays, they were named X-radiation or X-rays. X-rays are highly penetrating waves. They are widely used in radio- graphy (fig. 6.16) and in the medicinal field for diagnosis and therapeutic treatments. For example, X-rays can be used to destroy cancer cells. In industries, Fig. 6.18 Protective they are used to detect internal defects Fig. 6.17 Gamma rays are emitted during radio handling in metal coatings. decay processes such as explosions. 150e World Health the civironment. Moreover, ionizing WHO) has been continually radiation can also come from outer space. effects of electromagnetic radio Such radiation is called cosmic rays or the following are some of their key canuse mediation. On the other hand, First, external electric and nuclear power generation, nuclear testing, fields at the low-frequency reply, and the transportation and processing of electromagnetic spectrum indy 1. Why do intense, re circulating currents within your answer in tern nuclear wastes are artificial sources of . Differentiate the AN ionizing radiation. Consumer products such as TV sets, radioluminous watches, body. In almost all normal eng however, the levels of induced station broadcast m inside the body are only minitel AM station? and smoke detectors also emit artificial significant effects. Second, the Find the frequenci radiation. Furthermore, X-ray machines wavelengths: (a) 2 n and other medical devices also produce artificial radiation for medical diagnosis of radio waves is the heating of certain diseases, cancer treatment, and tissues. Third, exposure to extra levels of high-frequency electr scientific research. Radiation from the sun consists of fields, even only for a short per Doppler Effect different forms of non-ionizing radiation. seriously harmful to health. Electric and magnetic fe Recall what you have Power lines, electrical equipment, and wherever electricity is the velocity of an object and mobile phone systems also produce non- transmitted, or distributed fra and frequency of a sour ionizing radiation. Radiation cannot be removed from stations or is used in electrical ap Doppler effect considers bo (of the source relative to t the environment, but its risks can be The use of electricity is an inter the sound) and the propert controlled by understanding it. People of daily activities. It is further wave (wavelength and freq who are exposed to ionizing radiation with the accelerated evolution of The Doppler effect should observe safety protocols. As phone and telecommunication te in the frequency (or pitch a standard minimum rule, radiation Experts have been perceived by the observer warning symbols, such as the one shown extensive research, and no evite difference in the velocities in figure 6.19, should not be ignored. been found that indicates that and the sound source with to low levels of electromagnetic medium of wave propagation detrimental to human health. international research continues on investigating possible between cancer and electromap at power lines and radio free Nevertheless, the environmes be safeguarded from ham may arise from the explain electromagnetic radiation . Fur because artificial ionizing primarily caused by ongoing research and modern off Fig. 6.20 (a) The redshift phenomena Fig. 6.10 Radiation warning symbols are commonly whereas, (b) the blueshift p placed in potentially dangerous zones that are utmost vigilance should be of the light. (Illustration by exposed to high electromagnetic radiation. as technological advances 152 pursued for human consumplydiscusses the lex and the pray different region ffects on living the ment. Moreover Electromagnetic Waves: ward from the source in a straight line cation of visible Their Nature and Properties with the electric and magnetic fields ts. Furthermore, Electromagnetic radiation is energy oscillating perpendicular (at right angles) to each other and to the direction of ctromagnetism gas that is emitted by accelerating charged wave propagation. on of simple particles that produce oscillating You have learned in grade 8 electric and magnetic fields. It travels that waves can be categorized as through space or a material medium in electromagnetic waves or mechanical the form of electromagnetic waves. An waves based on whether they can or electrically charged particle, such as cannot travel through space. Mechanical an electron, generates an electric field, waves such as sound waves and seismic and lenses; which surrounds the charged particle. waves need a medium to propagate, and amming technic When the charged particle oscillates therefore cannot travel through space. (i.e., repeatedly moves back and On the other hand, electromagnetic waves the characteris forth), its electric field also oscillates such as radio waves and microwaves can images formet (fig. 6.1a). An oscillating electric field travel through space or a vacuum. produces an oscillating magnetic field. Recall that electromagnetic waves which the prop. Likewise, an oscillating magnetic field are transverse in nature. This means d lenses deter induces an oscillating electric field. that the waves move perpendicular to the al instruments, The interaction between the oscillating direction of wave propagation. For a quick electric and magnetic fields then creates review, let us discuss the basic parts of generation of an electromagnetic wave. Thus, an a wave . ent of a map electromagnetic wave, as its name Like any other type of transverse implies, consists of oscillating electric waves, electromagnetic waves are a series ation of a sing and magnetic fields (fig. 6.1b). of hills and valleys. The highest point of a Like all types of waves, electro- transverse wave is the crest, whereas its generator. magnetic waves carry energy from lowest point is the trough. place to another. The energy The maximum vertical displacement of electromagnetic waves is stored of the wave from its resting or equilibrium in the electric and magnetic fields. position is the amplitude. It is basically Electromagnetic waves propagate out- the height of the wave. The amount of electric field 2 = wavelength n of the magnetic direction field Earth's sub ion are reflect vibrating charged d bright-cale particle re absorbed electromagnetic wave fern techno a ic radiation Fig. 6.1 (a) A vibrating charged particle produces vibrating electric and magnetic fields, (b) which combine to the knowle create an electromagnetic wave. being app to seek cation(Hz), which is define and. One thousand th rtz (kHz), 1000 kit ertz (MHz), and 100 ahertz (GHz) In 1860, the Scottish physicist On the other hand, if 10 waves are f a wave is inversely James Clerk Maxwell (1831-1879; fig. produced in 1 s, with each wave having elength. This mean 6.4) studied electromagnetic waves and a wavelength of 3.0x107 m, then the calculated that their speed is identical frequency of oscillation will be 10 Hz. higher frequencies to the speed of light: 3.0x105 m/s. He In addition, electromagnetic waves that ths, whereas waves then proposed that light is a form of have a frequency of 1000 Hz will have a encies have longer electromagnetic radiation. Maxwell's 3.0x105 m wavelength. Therefore, the r wavelength has a unified theory of electromagnetism is higher the frequency of the vibrating use a cycle can be considered one of the most important charge is, the shorter is the wavelength period (fig. 6.30) contributions in physics. of the vibration. This relationship cycles can pass between frequency and wavelength is expressed as s. By contrast, lower frequency c= f2, longer period to where c is the speed of light, f is the wave cles can pass in a 5.36). frequency, and 2 is the wavelength. Sample Problem What is the frequency of a red laser beam with a wavelength of 7.4x10-7 m? Given 2 = 7.4 x107 m C = 3.0x 108 m/s Unknown Fig. 6.4 James Clerk Maxwell formulated the classical f = ? theory of electromagnetic radiation. Solution All types of electromagnetic waves C = fa travel in a vacuum or free space at the speed of light. However, they differ in f = T frequency and wavelength. The frequency of an electromagnetic wave as it vibrates 3.0x108 m/s through space is similar to the frequency 7.0x10-7 m of the oscillating electric charge that f = 4.29x10#4 Hz generates it. This means that an electric charge with a frequency of 1 vibration per second or 1 Hz will produce a wave Answer ecific point in The frequency of a red laser beam s in a specify with a wavelength of 3.0x108 m because with a wavelength of 7.4x107 m is the speed of the wave is 3.0x108 m/s. 4.29 x 10#4 Hz. 143over a wide range at extends ove curvature. He was awarded the Nobel waves sent by the transmitters of radio have the longer Prize in Physics in 1909 for his work or TV stations. with the German inventor and physicist There are two common methods e a few meters Karl Ferdinand Braun (1850-1918) on of sending audio information in radio electromagnetic the development of wireless telegraphy. waves: amplitude modulation (AM) encies that rang Radio waves are commonly used in technique and frequency modulation y 300 GHz. Maxwe communication. The transmission and (FM) technique. predicted th reception of radio waves rely on oscillating In the AM technique, radio stations aves in 1867. T charges. Transmission is facilitated by modulate or change the amplitude of inrich Hertz (185) radio and TV transmitters (fig. 6.6), which radio waves (carrier wave) they transmit ed his prediction operate on two basic transformations. First by feeding audio information called he Italian inventy is the transformation of sound energy and input or modulating signal into them. 874-1937) sent an light energy into electrical energy. Second Figure 6.7 shows that the upper and is the conversion of electrical energy into lower curves that trace the highest and ansatlantic wireless electromagnetic energy in the antenna lowest points of the resulting signal k was significant wire of transmitters. The change in the follow the outline of the modulating hat wireless ware velocity of the electrons in the antenna signal. In AM, although the amplitude of by the Earth wire produces a changing magnetic the carrier wave is varied, its frequency field. Radio and TV sets then receive the remains constant. no WW carrier wave fiation X-rays 10-10 modulating signal lecules atoms amplitude modulated wave (resulting signal) bond signals Fig. 6.7 The amplitude modulation technique involves rs detect e Fig changing the amplitude of the carrier wave to ansmitters transmit audio information to receivers.Of port dgid mulu at a wavew oihe's ustre 145On the other hand, in the FM Microwaves technique, radio stations modulate the Microwaves have long wavely Infrared Ra frequency of the carrier signal. When the frequency of the modulating signal with frequencies that range from In 1800 is imposed upon the carrier wave, the 1000 GHz. They were discovered astronomer Sir frequency of the combined wave is by Hertz, who first demonstrate 1822) studied changed (fig. 6.8). In FM, the amplitude existence by building an apparat temperature a and other parameters of the resulting produced and detected microwave visible spectrum UHF region. used a glass p signal remain constant. Microwaves can be into its compo communication purposes such thermometer long distance radio-relay systems, one extra ther way communication systems, and end of the spe safety operations (fig. 6.9). Tin experiment sho carrier wave communication systems are also that was placed in TV-relay systems, radar devices, the highest te discovered infr guided missiles. Microwaves can ala IR is adj used in cooking and heating (fig. 6.101 long-wavelengt invention of microwave ovens has red modulating signal to one-fourth the usual cooking time compared when using electric ovens frequency modulated wave (resulting signal) Fig. 6.8 The frequency modulation technique involves changing the frequency of the carrier wave by imposing a modulating signal into it. Fig. 6.9 Microwave antennas are used to bring The AM radio frequency band runs transmissions, which are from about 530 to 1710 kHz, whereas the used for communication purposes FM radio frequency band ranges from about 88 to 108 MHz. The AM band is characterized by medium frequency (MF) radio waves, whereas the FM Fig. 6.11 Therma band is considered a region of very high camera, frequency (VHF) radio waves. Television of temp (TV) bands also fall under the VHF objects region, and they range from about 54 to 890 MHz. In addition, cellular phones use radio waves in the ultra high frequency (UHF) band. an be used for heatin Fig. 6.10 Microwaves can be use 146dying & tion, FOLLOW-Up finding magne 1. Why do intense, repeated exposures to the sun result in sunburn? Explain your answer in terms of infrared and ultraviolet radiation. ns of 2. Differentiate the AM and FM bands in a radio. Why is the sound of an FM uces station broadcast more audible and of better quality compared with that of an he hum AM station? ironme 3. Find the frequencies of electromagnetic waves that have the following d cure wavelengths: (a) 2 m, (b) 25 m, and (c) 75 m. al to a main Ing ofi remelt Doppler Effect The Doppler effect also occurs in Recall what you have learned about cityofan object and the wavelength light waves. When a distant light source, The such as a star, is moving away relative arth, its frequency as observed from Thus, the light shifts Thisother ng charged wave propagati particles that produce oscillating You have le electric and magnetic fields. It travels that waves can Objectives through space or a material medium in electromagnetic wa At the end of this chapter, you are curved mirrors and the form of electromagnetic waves. An waves based on w electrically charged particle, such as cannot travel through apply ray diagramming an electron. generates an electric field, wares such as sour expected to 1. describe the different regions of the in describing the cho which surrounds the charged particle. waves need a medi electromagnetic spectrum; and positions of image When the charged particle oscillates therefore cannot tr lenses; (i.e., repeatedly moves back and On the other hand, 2. cite examples of practical applica- forth), its electric field also oscillates such as radio waves tions of the different regions of (fig. 6.10). An oscillating electric field travel through spac identify ways by which, produces an oscillating magnetic field, the electromagnetic spectrum, ties of mirrors and lenses Recall that el such as the use of radio waves in their use in optical instra Likewise, an oscillating magnetic field are transverse in induces an oscillating electric field. that the waves move telecommunications; demonstrate the generate, The interaction between the oscillating direction of wave pr 3. explain the effects of electromagnetic tricity by movement of electric and magnetic fields then creates review, let us disc radiation on living things and the through a coil; and an electromagnetic wave. Thus, an a wave. electromagnetic wave, as its name Like any other environment; explain the operation of. implies, consists of oscillating electric waves, electromagn predict the qualitative character- electric motor and generate and magnetic fields (fig. 6.16). of hills and valleys. istics of images formed by plane and Like all types of waves, electro- transverse wave is magnetic waves carry energy from lowest point is the tre one place to another. The energy The maximum Electromagnetic Radiation of electromagnetic waves is stored of the wave from its r in the electric and magnetic fields. position is the amp Electromagnetic waves propagate out- the height of the wa Electromagnetic radiation is a form learned, only a fraction of the A . wavelength of energy that humans encounter and radiation can reach Earth's utilize in day-to-day activities. It had because some of the radiation arena only been associated with visible light back to space by clouds and bright vibrating charged until scientists discovered its other types, aerosols, whereas others are absor particle electromagnetic wave which differ in frequency and wavelength. greenhouse gases. The light from mobile phones and the With the advent of modern tech heat that warm objects give off are types the nature of electromagnetic radiat Fig. 6.1 (a) A vibrating charged particle produces vibrating electric and magnetic fields, of electromagnetic radiation. been rigorously studied, and the know create an electromagnetic wav Electromagnetic radiation primarily scientists have gathered are being comes from extremely hot astronomical to improve human life and to seek objects such as the sun. As you have advanced technological applications 140the world d mixture spectrum Ultraviolet Radiation related activities. In response to this, an avelength international treaty called the Montrend ible light A year after Herschel discovered Protocol on Substances That Deplete lors of the infrared radiation, the German chemist the Ozone Layer was enforced in 1987. Johann Wilhelm Ritter (1776-1810) he visible The treaty was a landmark agreement discovered ultraviolet (UV) light. Ritter that is designed to eliminate the global sed in the was inspired by Herschel and sought to production, consumption, and emission of discover what was beyond the purple end ozone-depleting substances (ODSs) such as of the visible spectrum. chlorofluorocarbons (CFCs), Class II ODS The frequency of UV radiation and hydrochlorofluorocarbons (HCFCa). ranges from about 7.5x10" to These chemicals are also greenhouse 10 3.0x 1016 Hz. UV radiation is produced gases that contribute to global warming by by special lamps (figs. 6.14a and 6.146) trapping heat into the atmosphere. and extremely hot bodies. The sun emits The application of UV radiation has waves large amounts of UV radiation, which its own advantages. Controlled exposure has harmful effects on human health. to UV radiation can be used in the 10# Fortunately, most of the radiation treatment of some types of skin diseases. It received by Earth is absorbed by the can also be used in killing disease-causing avelength ozone layer in the atmosphere (fig. 6.15). microorganisms. Moreover, vitamin D. In 1985, it was reported that a hole which is essential for the development was discovered in the ozone layer over the of strong bones and teeth, is produced in Antarctic. The ozone hole was caused by the our bodies when 7-dehydrocholesterol (7- emission of certain human-made chemicals DHC) that is present in the skin interacts into the atmosphere through human- with UV radiation. Ilustration Ly UAC a UV-A 5% absorbed b absorbed by the ozone layer in the atmosphere. ssing plants. (Photograph a by Tarvo Fig. 6.15 The ultraviolet radiation from the sun is 149 Fig. 6.14 Ultraviolet lamps are used to sterilize air in food under CC BY-SA 3.0)Radio Waves curvature. H Electromagnetic Spectrum Radio waves cover a wide range Prize in Ph of wavelengths that extends over with the Ger Electromagnetic radiation encom- Karl Ferdin passes a range of energies that has distinct several bands. They have the longest the developn wavelengths and frequencies known as the electromagnetic spectrum (fig. 6.5). wavelengths, from a few meters to kilometers, in the electromagnetic Radio The seven regions of the electromagnetic spectrum with frequencies that range communicat spectrum are the radio waves, microwaves, reception of infrared radiation, visible light, ultraviolet from about 3 kHz to 300 GHz. Maxwell had mathematically predicted the charges. Tra (UV) radiation, X-rays, and gamma rays. existence of radio waves in 1867. The radio and T These energies are used in many advanced technological applications, such as in German physicist Heinrich Hertz (1857- operate on t is the trans cellular phones, radio, X-ray machines, 1894) then confirmed his prediction pacemakers, and wireless network in 1887. In 1901, the Italian inventor light energy routers. The properties of each type of Guglielmo Marconi (1874-1937) sent and is the conve electromagnetic wave determine their received the first transatlantic wireless electromag capability to travel through a different message. His work was significant wire of tra medium, their heating effects, and their because it proved that wireless waves velocity of impacts on living tissues. were not affected by the Earth's wire prod field. Radi penetrates the yes no yes no Earth's atmosphere radiation type radio waves microwaves IR radiation wavelength (m) 103 10-2 10-5 visible light UV radiation X-rays 0.5x10- gamma rays 10-8 10-10 10-2 approximate scale of wavelength buildings humans butterflies needle protozoans mole point atomic frequency (Hz) nuclei 10' 10 1012 temperature of objects 1015 103 at which this radiation is the most intense wavelength emitted 1K -2720 .C 100 K 10000 K -173 .C 9727 C Fig. 6.5 The electromagnetic spectrum ranges from radio waves to gamma rays. (Illustration NASA is licensed under CC BY-SA 3.0) FI 144