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Review and Reinforce Waves of the Electromagnetic Spectrum

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Section Learning Objectives

By the end of this department, you will be able to do the following:

  • Define the electromagnetic spectrum, and describe it in terms of frequencies and wavelengths
  • Draw and explicate the differences and similarities of each section of the electromagnetic spectrum and the applications of radiations from those sections

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The learning objectives in this section volition help your students chief the following standards

  • (7) Science concepts. The student knows the characteristics and behavior of waves. The student is expected to:
    • (A) examine and draw oscillatory motion and wave propagation in various types of media;
    • (B) investigate and clarify characteristics of waves, including velocity, frequency, amplitude, and wavelength, and calculate using the relationship betwixt wave speed, frequency, and wavelength;
    • (C) compare characteristics and behaviors of transverse waves, including electromagnetic waves and the electromagnetic spectrum, and characteristics and behaviors of longitudinal waves, including sound waves; and
    • (F) depict the role of wave characteristics and behaviors in medical and industrial applications.

In improver, the High School Physics Laboratory Manual addresses content in this department in the lab titled: Low-cal and Color, as well as the following standards:

  • (7) Science concepts. The pupil knows the characteristics and behavior of waves. The student is expected to
    • (C) compare characteristics and behaviors of transverse waves, including electromagnetic waves and the electromagnetic spectrum, and characteristics and behaviors of longitudinal waves, including sound waves.
  • (8) Science concepts. The student knows simple examples of diminutive, nuclear, and breakthrough phenomena. The student is expected to
    • (B) compare and explain the emission spectra produced by diverse atoms.

Department Key Terms

electric field electromagnetic radiation (EMR) magnetic field Maxwell'southward equations

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[BL]Explicate that the term spectrum refers to a physical property that has a wide range with values that are continuous in some cases and, in other cases, discrete. Ask for other examples of spectra, for instance, sound, people'due south heights, etc.

[OL]Ask students to name ways that sunlight affects Earth. Provide examples that students don't name: photosynthesis, weather, climate, seasons, warming, etc. Discuss energy transformations that take place later light enters the atmosphere, such as transformations in food chains and ecosystems. Ask students if they can explain how the free energy in fossil fuels was originally calorie-free energy.

Misconception Alert

The light we can run across is chosen visible light. Dispel any misconceptions that visible calorie-free is somehow different from radiations we cannot see, except for frequency and wavelength. The fact that some radiation is visible has to practice with how the eye functions, not with the radiation itself.

The Electromagnetic Spectrum

We generally take light for granted, only it is a truly astonishing and mysterious course of energy. Remember about it: Light travels to Earth across millions of kilometers of empty space. When it reaches us, it interacts with matter in various ways to generate virtually all the energy needed to support life, provide heat, and cause weather condition patterns. Light is a form of electromagnetic radiation (EMR). The term lite ordinarily refers to visible lite, just this is not the only course of EMR. As we will see, visible lite occupies a narrow band in a broad range of types of electromagnetic radiation.

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[OL]Discuss electrical, magnetic, and gravitational fields. Point out how these three fields are similar, and how they differ.

[AL]Draw vectors as having magnitude and direction, and explicate that fields are vector quantities. In these cases, the fields are made upwardly of forces acting in a direction.

Electromagnetic radiations is generated past a moving electrical charge, that is, by an electric electric current. Every bit you will run into when you written report electricity, an electrical current generates both an electrical field, E, and a magnetic field, B. These fields are perpendicular to each other. When the moving charge oscillates, as in an alternate electric current, an EM wave is propagated. Effigy 15.2 shows how an electromagnetic moving ridge moves away from the source—indicated by the ~ symbol.

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[BL]Review wave properties: frequency, wavelength, and amplitude. Inquire students to recall sound and water waves, and explain how they relate to these properties.

[OL]Explain that an important difference between EM waves and other waves is that they can travel beyond empty space.

[AL]Ask if students recall the differences between longitudinal and transverse waves. Give examples. Explicate that waves behave energy, not matter.

Watch Physics

Electromagnetic Waves and the Electromagnetic Spectrum

This video, link beneath, is closely related to the following effigy. If you lot accept questions well-nigh EM wave properties, the EM spectrum, how waves propagate, or definitions of any of the related terms, the answers tin can be constitute in this video.

Grasp Check

In an electromagnetic wave, how are the magnetic field, the electric field, and the direction of propagation oriented to each other?

  1. All three are parallel to each other and are forth the x-axis.
  2. All 3 are mutually perpendicular to each other.
  3. The electric field and magnetic fields are parallel to each other and perpendicular to the direction of propagation.
  4. The magnetic field and management of propagation are parallel to each other along the y-axis and perpendicular to the electric field.

Instructor Back up

Teacher Support

Direct students to use this video as a mode of connecting to the data in the following two figures, equally well as to the post-obit table.

Virtual Physics

Radio Waves and Electromagnetic Fields

This simulation demonstrates wave propagation. The EM wave is propagated from the broadcast belfry on the left, but every bit in Figure 15.ii. You lot can brand the wave yourself or allow the animation to transport it. When the wave reaches the antenna on the right, it causes an aquiver current. This is how radio and television set signals are transmitted and received.

Grasp Check

Where do radio waves fall on the electromagnetic spectrum?

  1. Radio waves have the same wavelengths as visible calorie-free.
  2. Radio waves fall on the high-frequency side of visible low-cal.
  3. Radio waves fall on the short-wavelength side of visible lite.
  4. Radio waves autumn on the low-frequency side of visible light.

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Teacher Back up

Connect the discussion from the previous video, in which the generation of an electromagnetic wave is described, to this application of transmission and reception of electromagnetic waves. In particular, point out how the reception of the radio moving ridge is substantially identical to the method by which the wave is generated. Explain as well that these electromagnetic waves are the carrier waves on which sound or visual signals—either analog or digital—are placed, and so that they can be transmitted to receivers inside a certain range of the broadcast antenna.

The diagram shows two intersecting planes: a vertical plane labeled

Effigy fifteen.ii A office of the electromagnetic wave sent out from an oscillating charge at 1 instant in fourth dimension. The electric and magnetic fields (Eastward and B) are in phase, and they are perpendicular to each other and to the management of propagation. For clarity, the waves are shown simply along one direction, merely they propagate out in other directions too.

From your study of audio waves, recall these features that apply to all types of waves:

  • Wavelength—The distance between two wave crests or two wave troughs, expressed in various metric measures of distance
  • Frequency—The number of wave crests that laissez passer a bespeak per second, expressed in hertz (Hz or s–i)
  • Aamplitude: The height of the crest above the null point

As mentioned, electromagnetic radiations takes several forms. These forms are characterized by a range of frequencies. Because frequency is inversely proportional to wavelength, any form of EMR can also be represented by its range of wavelengths. Figure 15.3 shows the frequency and wavelength ranges of various types of EMR. With how many of these types are y'all familiar?

This figure shows the electromagnetic spectrum between two parallel, horizontal lines. The lower line, labeled

Effigy 15.iii The electromagnetic spectrum, showing the major categories of electromagnetic waves. The range of frequencies and wavelengths is remarkable. The dividing line between some categories is distinct, whereas other categories overlap.

Take a few minutes to study the positions of the various types of radiation on the EM spectrum, above. Sometimes all radiation with frequencies lower than those of visible light are referred to equally infrared (IR) radiation. This includes radio waves, which overlap with the frequencies used for media broadcasts of Tv set and radio signals. The microwave radiations that you lot see on the diagram is the same radiation that is used in a microwave oven. What we feel as radiant estrus is too a form of depression-frequency EMR.

Instructor Support

Teacher Support

[BL]Notice that most harmful forms of EM radiation are on the high-frequency end of the spectrum.

[OL]Enquire which forms of EM radiation students take heard nigh. Enquire them to describe the types of radiation they recollect, and correct any misconceptions. Talk over the difference between ionizing radiations and nonionizing radiation, and the deviation betwixt electromagnetic radiation and other types of radiation—blastoff, beta, etc.

Misconception Alert

Rut waves, a type of infrared radiations, are basically no dissimilar from other EM waves. We feel them every bit estrus because they have a frequency that interacts with our bodies in a way that transforms EM free energy into thermal energy.

All the high-frequency radiations to the right of visible low-cal is sometimes referred to as ultraviolet (UV) radiation. This includes X-rays and gamma (γ) rays. The narrow band that is visible light extends from lower-frequency red light to college-frequency violet light, thus the terms are infrared (below red) and ultraviolet (across violet).

Boundless Physics

Maxwell's Equations

The Scottish physicist James Clerk Maxwell (1831–1879) is regarded widely to have been the greatest theoretical physicist of the nineteenth century. Although he died young, Maxwell non only formulated a complete electromagnetic theory, represented by Maxwell's equations, he also developed the kinetic theory of gases, and made significant contributions to the agreement of colour vision and the nature of Saturn's rings.

Maxwell brought together all the work that had been done by brilliant physicists, such equally Ørsted, Coulomb, Ampere, Gauss, and Faraday, and added his ain insights to develop the overarching theory of electromagnetism. Maxwell's equations are paraphrased here in words because their mathematical content is beyond the level of this text. Withal, the equations illustrate how evidently simple mathematical statements tin can elegantly unite and express a multitude of concepts—why mathematics is the linguistic communication of science.

Maxwell's Equations

  1. Electric field lines originate on positive charges and cease on negative charges. The electric field is defined as the force per unit of measurement accuse on a test charge, and the strength of the force is related to the electric constant, ε 0.
  2. Magnetic field lines are continuous, having no beginning or finish. No magnetic monopoles are known to exist. The forcefulness of the magnetic force is related to the magnetic constant, μ 0.
  3. A changing magnetic field induces an electromotive strength (emf) and, hence, an electric field. The management of the emf opposes the alter, changing direction of the magnetic field.
  4. Magnetic fields are generated by moving charges or past changing electrical fields.

Maxwell's complete theory shows that electrical and magnetic forces are not separate, but unlike manifestations of the aforementioned thing—the electromagnetic force. This classical unification of forces is one motivation for current attempts to unify the four basic forces in nature—the gravitational, electromagnetic, strong nuclear, and weak nuclear forces. The weak nuclear and electromagnetic forces take been unified, and further unification with the potent nuclear force is expected; but, the unification of the gravitational force with the other iii has proven to exist a real caput-scratcher.

One last accomplishment of Maxwell was his evolution in 1855 of a process that could produce color photographic images. In 1861, he and photographer Thomas Sutton worked together on this procedure. The color image was accomplished by projecting red, blue, and green light through black-and-white photographs of a tartan ribbon, each photograph itself exposed in unlike-colored low-cal. The final image was projected onto a screen (come across Figure 15.4).

Photograph of a tartan ribbon tied like a bow.

Figure 15.4 Maxwell and Sutton'due south photograph of a colored ribbon. This was the first durable color photograph. The plaid tartan of the Scots made a colorful photographic subject.

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Features that encouraged mathematicians and physicists to have Maxwell's equations is that they are seen as existence both elegant and—considering the difference between an electric charge and a magnetic dipole, which give rise to the respective fields—essentially symmetrical. When scientists are looking for an approach to developing a new theory, they usually begin with the simplest and virtually symmetrical explanations. An case of such symmetry is the fact that electrons and protons take equal and opposite charges. You can see the symmetry in the iv statements, given above, that describe the equations. The get-go two statements show a like treatment of electrical and magnetic fields, and the last two describe how a magnetic field can generate an electrical field, and vice versa.

From our present-24-hour interval perspective, nosotros can now come across the significance of Maxwell's equations. This was the first footstep in the quest to unify all natural forces under one theory. Later Maxwell unified the electric and magnetic forces as the electromagnetic forcefulness, others unified this force with the weak nuclear force, and there is show that the strong nuclear force can exist unified with the electroweak strength. The only strength that has resisted unification with the others is the gravitational forcefulness. A theory that would unify all forces is often referred as a 1000 unified theory or a theory of everything. The quest for such a theory is still underway.

Describe electromagnetic force equally explained by Maxwell's equations.

  1. Co-ordinate to Maxwell's equations, electromagnetic strength gives rising to electrical force and magnetic force.

  2. Co-ordinate to Maxwell's equations, electric force and magnetic force are different manifestations of electromagnetic force.

  3. Co-ordinate to Maxwell's equations, electric force is the crusade of electromagnetic force.

  4. Co-ordinate to Maxwell'due south equations, magnetic strength is the cause of electromagnetic force.

Characteristics of Electromagnetic Radiation

All the EM waves mentioned higher up are basically the same form of radiation. They can all travel across empty space, and they all travel at the speed of light in a vacuum. The bones divergence between types of radiation is their differing frequencies. Each frequency has an associated wavelength. As frequency increases across the spectrum, wavelength decreases. Energy also increases with frequency. Because of this, higher frequencies penetrate matter more readily. Some of the properties and uses of the various EM spectrum bands are listed in Table 15.1.

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Teacher Support

[BL]Explain transparency and opacity. Discuss how some materials are transparent to certain frequencies but opaque to others. Enquire students for examples of materials that can be penetrated by some EM frequencies but not by others. Enquire for examples of materials that are transparent to visible light and materials that are opaque to visible light.

[OL]Ask students why a lead apron is laid beyond dental patients during dental 10-rays. Explain that 10-rays are at the loftier-energy end of the spectrum and that they are very penetrating. They are but stopped by very dense materials, such as atomic number 82.

[AL]Ask if students can explain Globe's greenhouse effect in terms of the penetrating power of various frequencies of EM radiation. Explain that the atmosphere is more transparent to visible light than to heat waves. Visible calorie-free penetrates the atmosphere and warms Earth'south surface. The heated surface radiates oestrus waves, which are trapped partially by sure gases in the atmosphere.

Types of EM Waves Production Applications Life Sciences Aspect Issues
Radio and TV Accelerating charges Communications, remote controls MRI Requires controls for band use
Microwaves Accelerating charges & thermal agitation Communications, microwave ovens, radar Deep heating Prison cell telephone employ
Infrared Thermal agitation & electronic transitions Thermal imaging, heating Absorption past atmosphere Greenhouse consequence
Visible Light Thermal agitation & electronic transitions All pervasive Photosynthesis, human vision
Ultraviolet Thermal agitation & electronic transitions Sterilization, slowing abnormal growth of cells Vitamin D production Ozone depletion, causes cell damage
X-rays Inner electronic transitions & fast collisions Medical, security Medical diagnosis, cancer therapy Causes cell damage
Gamma Rays Nuclear disuse Nuclear medicine, security Medical diagnosis, cancer therapy Causes cell damage, radiation impairment

Tabular array 15.1 Electromagnetic Waves This table shows how each type of EM radiations is produced, how it is applied, as well every bit environmental and wellness issues associated with it.

The narrow ring of visible lite is a combination of the colors of the rainbow. Figure 15.five shows the section of the EM spectrum that includes visible low-cal. The frequencies corresponding to these wavelengths are iv.0 × x 14  due south −one 4.0 × 10 xiv  s −i at the blood-red end to seven.9 × 10 14  south −one 7.9 × 10 xiv  s −1 at the violet end. This is a very narrow range, considering that the EM spectrum spans virtually 20 orders of magnitude.

This diagram focuses on the visible section of the electromagnetic spectrum. A horizontal arrow represents wavelengths of light decreasing from left to right. The arrow is calibrated with numbers ranging from 800 on the left to 300 on the right, and the line is labeled with the Greek letter lambda, followed by the letters n m in parentheses. Above the arrow is a colored band stretching from about 760 up to about 420. The band, labeled as

Figure xv.five A small role of the electromagnetic spectrum that includes its visible components. The divisions betwixt infrared, visible, and ultraviolet are not perfectly distinct, nor are the divisions between the seven rainbow colors

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Teacher Back up

[BL]Review the main and secondary colors of pigments. Note that this is subtractive color mixing.

[OL]Explain the difference betwixt subtractive and additive color mixing. The colors on the subtractive color bike are made by pigments that absorb all colors but one. Therefore, when these colors all overlap, all light is absorbed and the result is black. White low-cal is a combination of all colors, so when all colors are added together on the additive color wheel, the result is white. Explain that cyan is a shade of bluish and that magenta is a shade of red.

Tips For Success

Wavelengths of visible low-cal are often given in nanometers, nm. One nm equals 10 −9 10 −9 m. For instance, yellow light has a wavelength of about 600 nm, or 6 × 10 −7 half dozen × 10 −seven g.

As a child, y'all probably learned the color wheel, shown on the left in Effigy 15.6. It helps if you know what color results when yous mix different colors of paint together. Mixing two of the primary pigment colors—magenta, yellow, or cyan—together results in a secondary color. For example, mixing cyan and xanthous makes greenish. This is chosen subtractive color mixing. Mixing different colors of light together is quite different. The diagram on the right shows additive color mixing. In this instance, the principal colors are cherry-red, green, and blue, and the secondary colors are cyan, magenta, and yellowish. Mixing pigments and mixing low-cal are different considering materials absorb light by a different set of rules than does the perception of calorie-free past the center. Notice that, when all colors are subtracted, the outcome is no color, or black. When all colors are added, the event is white calorie-free. We see the opposite of this when white sunlight is separated into the visible spectrum by a prism or by raindrops when a rainbow appears in the sky.

The figure shows two panels arranged side by side. Each panel consists of three overlapping circles, arranged such that the intersection of any two circles passes through the center of the third circle. The left panel, labeled

Figure 15.six Mixing colored pigments follows the subtractive colour bike, and mixing colored light follows the condiment color wheel.

Virtual Physics

Colour Vision

This video demonstrates additive color and color filters. Try all the settings except Photons.

PhET Explorations: Color Vision. Brand a whole rainbow by mixing red, dark-green, and blue light. Change the wavelength of a monochromatic beam or filter white low-cal. View the calorie-free as a solid beam, or see the private photons.

Ordinary white light is a combination of all colors of visible light. How would a bluish absorption filter placed in front of a white light source affect the light you observe?

  1. A bluish filter absorbs bluish light, causing the observed light to exist a combination of the other colors.

  2. A blue filter absorbs the contrary color of light—orange, causing the observed light to exist blue.

  3. A blueish filter permits only bluish light to pass though, absorbing the other colors and leaving blueish light for the observer.

  4. A bluish filter permits simply the opposite color calorie-free—orange—to pass through, leaving orange calorie-free for the observer.

Teacher Support

Teacher Back up

Have students adjust the unlike colored lights for the RGB bulb simulation, first with individual settings, then with combinations of two and three colors to encounter what colors result and are perceived. Similarly, with the Single Bulb simulation, have students note how different filter settings affect what colors are seen for light with different colour components.

Humans have found uses for every part of the electromagnetic spectrum. Nosotros will have a await at the uses of each range of frequencies, first with visible lite. Most of our uses of visible calorie-free are obvious; without it our interaction with our surroundings would exist much unlike. We might forget that nearly all of our food depends on the photosynthesis process in plants, and that the energy for this process comes from the visible part of the spectrum. Without photosynthesis, we would also take almost no oxygen in the atmosphere.

Instructor Support

Teacher Support

[BL]Ask how dissimilar frequencies of EM radiations are applied. Name each frequency range, and enquire the students to supply the application, for case, 10-rays used in medical imaging.

[OL]Ask students if they know why low-frequency radiation generally has dissimilar uses than high-frequency radiation. Explain that it has to do with penetrating power, which is related to wellness hazards.

[AL]Mention the ranges of Television set signals designated very high frequency (VHF) and ultrahigh frequency (UHF). Explain that these frequencies are but relatively high compared to radio broadcast frequencies. Their place in the whole EM spectrum is at the low end.

The low-frequency, infrared region of the spectrum has many applications in media dissemination. Television, radio, jail cell phone, and remote-command devices all broadcast and/or receive signals with these wavelengths. AM and FM radio signals are both low-frequency radiation. They are in different regions of the spectrum, only that is non their basic difference. AM and FM are abbreviations for amplitude modulation and frequency modulation . Information in AM signals has the grade of changes in aamplitude of the radio waves; information in FM signals has the form of changes in moving ridge frequency.

Another awarding of long-wavelength radiation is institute in microwave ovens. These appliances cook or warm food by irradiating it with EM radiation in the microwave frequency range. Near kitchen microwaves utilize a frequency of 2.45 × 10 ix 2.45 × 10 9 Hz. These waves accept the right amount of energy to cause polar molecules, such equally water, to rotate faster. Polar molecules are those that have a partial charge separation. The rotational energy of these molecules is given upward to surrounding affair every bit heat. The first microwave ovens were called Radaranges because they were based on radar technology developed during Globe State of war II.

Radar uses radiation with wavelengths similar to those of microwaves to detect the location and speed of afar objects, such as airplanes, weather formations, and motor vehicles. Radar information is obtained by receiving and analyzing the echoes of microwaves reflected past an object. The speed of the object can be measured using the Doppler shift of the returning waves. This is the same result y'all learned about when you studied sound waves. Like sound waves, EM waves are shifted to college frequencies past an object moving toward an observer, and to lower frequencies by an object moving abroad from the observer. Astronomers use this same Doppler upshot to measure the speed at which afar galaxies are moving away from us. In this case, the shift in frequency is called the reddish shift, because visible frequencies are shifted toward the lower-frequency, red end of the spectrum.

Exposure to whatsoever radiation with frequencies greater than those of visible low-cal carries some wellness hazards. All types of radiation in this range are known to crusade cell damage. The danger is related to the loftier free energy and penetrating ability of these EM waves. The likelihood of existence harmed by any of this radiation depends largely on the amount of exposure. Most people endeavor to reduce exposure to UV radiation from sunlight by using sunscreen and protective clothing. Physicians still utilise X-rays to diagnose medical issues, but the intensity of the radiations used is extremely low. Effigy 15.8 shows an X-ray prototype of a patient'southward chest crenel.

Ane medical-imaging technique that involves no danger of exposure is magnetic resonance imaging (MRI). MRI is an of import imaging and research tool in medicine, producing highly detailed two- and iii-dimensional images. Radio waves are circulate, absorbed, and reemitted in a resonance process that is sensitive to the density of nuclei, usually hydrogen nuclei—protons.

This figure is an X-ray of a person's chest cavity. It includes the outlines of artificial heart valves, a pacemaker, and some wires.

Figure fifteen.8 This shadow X-ray image shows many interesting features, such as bogus heart valves, a pacemaker, and wires used to close the sternum. (credit: P.P. Urone)

Bank check Your Understanding

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Teacher Back up

Use these questions to assess student achievement of the section's Learning Objectives. If students are struggling with a specific objective, these questions volition assistance identify any gaps and straight students to the relevant content.

i .

Place the fields produced by a moving charged particle.

  1. Both an electrical field and a magnetic field will be produced.
  2. Neither a magnetic field nor an electric field will be produced.
  3. A magnetic field, but no electric field volition be produced.
  4. Only the electric field, but no magnetic field will be produced.

2 .

X-rays comport more free energy than visible light. Compare the frequencies and wavelengths of these two types of EM radiation.

  1. Visible calorie-free has college frequencies and shorter wavelengths than X-rays.

  2. Visible light has lower frequencies and shorter wavelengths than X-rays.

  3. Visible light has higher frequencies and longer wavelengths than X-rays.

  4. Visible calorie-free has lower frequencies and longer wavelengths than X-rays.

iii .

How does wavelength change as frequency increases across the EM spectrum?

  1. The wavelength increases.

  2. The wavelength commencement increases and and so decreases.

  3. The wavelength start decreases and and so increases.

  4. The wavelength decreases.

iv .

Why are Ten-rays used in imaging of broken basic, rather than radio waves?

  1. X-rays have higher penetrating energy than radio waves.

  2. X-rays have lower penetrating free energy than radio waves.

  3. X-rays take a lower frequency range than radio waves.

  4. X-rays accept longer wavelengths than radio waves.

5 .

Identify the fields that make up an electromagnetic moving ridge.

  1. both an electric field and a magnetic field

  2. neither a magnetic field nor an electrical field

  3. only a magnetic field, but no electric field

  4. only an electrical field, but no magnetic field

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Source: https://openstax.org/books/physics/pages/15-1-the-electromagnetic-spectrum

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