The Electromagnetic Spectrum, Light | Physics

Learning objectives

Teacher Support

The learning objectives in this section will help your students master the following standards

(7) Science concepts. The student knows the characteristics and behavior of waves. The student is expected to:
- (A) examine and describe oscillatory motion and wave propagation in various types of media;
- (B) investigate and analyze characteristics of waves, including velocity, frequency, amplitude, and wavelength, and calculate using the relationship between 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) describe the role of wave characteristics and behaviors in medical and industrial applications.

In addition, the High School Physics Laboratory Manual addresses content in this section in the lab titled: Light and Color, as well as the following standards:

(7) Science concepts. The student 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 atomic, nuclear, and quantum phenomena. The student is expected to
- (B) compare and explain the emission spectra produced by various atoms.

Section Key Terms

electric field

electromagnetic radiation (EMR)

magnetic field

Maxwell’s equations

Teacher Support

[BL]Explain that the term spectrum refers to a physical property that has a broad range with values that are continuous in some cases and, in other cases, discrete. Ask for other examples of spectra, for example, sound, people’s 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 after light enters the atmosphere, such as transformations in food chains and ecosystems. Ask students if they can explain how the energy in fossil fuels was originally light energy.

The Electromagnetic Spectrum

We generally take light for granted, but it is a truly amazing and mysterious form of energy. Think 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 almost all the energy needed to support life, provide heat, and cause weather patterns. Light is a form of electromagnetic radiation (EMR). The term light usually refers to visible light, but this is not the only form of EMR. As we will see, visible light occupies a narrow band in a broad range of types of electromagnetic radiation.

Electromagnetic radiation is generated by a moving electric charge, that is, by an electric current. As you will see when you study electricity, an electric current generates both an electric field, E, and a magnetic field, B. These fields are perpendicular to each other. When the moving charge oscillates, as in an alternating current, an EM wave is propagated. Figure_15_01_EMwave shows how an electromagnetic wave moves away from the source—indicated by the ~ symbol.

Electromagnetic Waves and the Electromagnetic Spectrum

This video, link below, is closely related to the following figure. If you have questions about EM wave properties, the EM spectrum, how waves propagate, or definitions of any of the related terms, the answers can be found in this video.

Electromagnetic waves and the electromagnetic spectrum | Physics | Khan Academy

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

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

Radio Waves and Electromagnetic Fields

This simulation demonstrates wave propagation. The EM wave is propagated from the broadcast tower on the left, just as in Figure_15_01_EMwave. You can make the wave yourself or allow the animation to send it. When the wave reaches the antenna on the right, it causes an oscillating current. This is how radio and television signals are transmitted and received.

Where do radio waves fall on the electromagnetic spectrum?

Radio waves have the same wavelengths as visible light.
Radio waves fall on the high-frequency side of visible light.
Radio waves fall on the short-wavelength side of visible light.
Radio waves fall on the low-frequency side of visible light.

View original figure (external; image not reproduced in this text edition)

Original figure description: The diagram shows two intersecting planes: a vertical plane labeled “E” and a horizontal plane labeled “B”. The line of intersection is drawn as an arrow, with the letter “c” next to the arrowhead. Within the vertical plane are the crest, trough, and crest of a blue wave, enclosing arrows that point from the baseline to the line of the wave. Likewise, within the horizontal plane are the crest, trough, and crest of a red wave, enclosing arrows that point from the baseline to the line of the wave. To the left of the intersecting planes is a thin vertical bar with a small circle in the middle and a wave symbol within the circle.

A part of the electromagnetic wave sent out from an oscillating charge at one instant in time. The electric and magnetic fields (E and B) are in phase, and they are perpendicular to each other and to the direction of propagation. For clarity, the waves are shown only along one direction, but they propagate out in other directions too.

From your study of sound 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 pass a point per second, expressed in hertz (Hz or s^–1)
Amplitude: The height of the crest above the null point

As mentioned, electromagnetic radiation 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_01_EMSpectrum shows the frequency and wavelength ranges of various types of EMR. With how many of these types are you familiar?

View original figure (external; image not reproduced in this text edition)

Original figure description: This figure shows the electromagnetic spectrum between two parallel, horizontal lines. The lower line, labeled “Frequency (Hz)”, is calibrated in increments that increase by 100-fold, starting from 10 superscript 0 at the extreme left and ending beyond 10 superscript 24 on the extreme right. The upper line, labeled “Wavelength”, is calibrated in increments that decrease by 100-fold, starting from 3 times 10 superscript 6 on the left and ending with 3 times 10 superscript minus 14 on the right. Each wavelength measure has the unit “m” after it. The various categories of the spectrum are written between the parallel lines, with a double-headed arrow showing the range of each category. Starting from the left, they are: “Radio waves”, “Infrared”, “Visible light”, “Ultraviolet”, “X rays”, and “gamma rays”. Within the range for “Radio waves” are the subcategories labeled as “AM radio”, “TV”, and “Microwaves”. Within the range for “TV” is the subcategory FM radio.

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. The narrow band that is visible light extends from lower-frequency red light to higher-frequency violet light. Frequencies just below the visible are called infrared (below red) and those just above are ultraviolet (beyond violet). Radio waves, which overlap with the frequencies used for media broadcasts of TV and radio signals, occupy frequencies even lower than infrared (IR). The microwave radiation that you see on the diagram is the same radiation that is used in a microwave oven. What we feel as radiant heat is also a form of low-frequency EMR. The high-frequency radiation to the right of ultraviolet (UV) includes X-rays and gamma (γ) rays.

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 not 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 understanding of color vision and the nature of Saturn’s rings.

Maxwell brought together all the work that had been done by brilliant physicists, such as Ørsted, Coulomb, Ampere, Gauss, and Faraday, and added his own 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. However, the equations illustrate how apparently simple mathematical statements can elegantly unite and express a multitude of concepts—why mathematics is the language of science.

Maxwell’s Equations

Electric field lines originate on positive charges and terminate on negative charges. The electric field is defined as the force per unit charge on a test charge, and the strength of the force is related to the electric constant, ε₀.
Magnetic field lines are continuous, having no beginning or end. No magnetic monopoles are known to exist. The strength of the magnetic force is related to the magnetic constant, μ₀.
A changing magnetic field induces an electromotive force (emf) and, hence, an electric field. The direction of the emf opposes the change, changing direction of the magnetic field.
Magnetic fields are generated by moving charges or by changing electric fields.

Maxwell’s complete theory shows that electric and magnetic forces are not separate, but different manifestations of the same 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 have been unified, and further unification with the strong nuclear force is expected; but, the unification of the gravitational force with the other three has proven to be a real head-scratcher.

One final accomplishment of Maxwell was his development in 1855 of a process that could produce color photographic images. In 1861, he and photographer Thomas Sutton worked together on this process. The color image was achieved by projecting red, blue, and green light through black-and-white photographs of a tartan ribbon, each photo itself exposed in different-colored light. The final image was projected onto a screen (see Figure_15_01_FirstColor).

View original figure (external; image not reproduced in this text edition)

Original figure description: Photograph of a tartan ribbon tied like a bow.

Maxwell and Sutton’s photograph of a colored ribbon. This was the first durable color photograph. The plaid tartan of the Scots made a colorful photographic subject.

Teacher Support

Features that encouraged mathematicians and physicists to accept Maxwell’s equations is that they are seen as being 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 most symmetrical explanations. An example of such symmetry is the fact that electrons and protons have equal and opposite charges. You can see the symmetry in the four statements, given above, that describe the equations. The first two statements show a similar treatment of electric and magnetic fields, and the last two describe how a magnetic field can generate an electric field, and vice versa.

From our present-day perspective, we can now see the significance of Maxwell’s equations. This was the first step in the quest to unify all natural forces under one theory. After Maxwell unified the electric and magnetic forces as the electromagnetic force, others unified this force with the weak nuclear force, and there is evidence that the strong nuclear force can be unified with the electroweak force. The only force that has resisted unification with the others is the gravitational force. A theory that would unify all forces is often referred as a grand unified theory or a theory of everything. The quest for such a theory is still underway.

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Characteristics of Electromagnetic Radiation

All the EM waves mentioned above 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 basic difference 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_01.

Teacher Support

[BL]Explain transparency and opacity. Discuss how some materials are transparent to certain frequencies but opaque to others. Ask students for examples of materials that can be penetrated by some EM frequencies but not by others. Ask 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 across dental patients during dental X-rays. Explain that X-rays are at the high-energy end of the spectrum and that they are very penetrating. They are only stopped by very dense materials, such as lead.

[AL]Ask if students can explain Earth’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 light penetrates the atmosphere and warms Earth’s surface. The heated surface radiates heat waves, which are trapped partially by certain gases in the atmosphere.

This table shows how each type of EM radiation is produced, how it is applied, as well as environmental and health issues associated with it.

Electromagnetic Waves
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	Cell phone use
Infrared	Thermal agitation & electronic transitions	Thermal imaging, heating	Absorption by atmosphere	Greenhouse effect
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 decay	Nuclear medicine, security	Medical diagnosis, cancer therapy	Causes cell damage, radiation damage

The narrow band of visible light is a combination of the colors of the rainbow. Figure_15_01_Visible shows the section of the EM spectrum that includes visible light. The frequencies corresponding to these wavelengths are $4.0 \times 10^{14} s^{−1}$ at the red end to $7.9 \times 10^{14} s^{−1}$ at the violet end. This is a very narrow range, considering that the EM spectrum spans about 20 orders of magnitude.

View original figure (external; image not reproduced in this text edition)

Original figure description: 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 “Visible light”, shows colors labeled as “Red”, “Orange”, “Yellow”, “Green”, “Blue”, and “Violet”. To the left of the band is a region labeled as “Infrared”, above the 800 mark. To the right of the band is a region labeled as “Ultraviolet”, above the 300 mark.

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 the divisions between the seven rainbow colors

As a child, you probably learned the color wheel, shown on the left in Figure_15_01_Color. It helps if you know what color results when you 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 yellow makes green. This is called subtractive color mixing. Mixing different colors of light together is quite different. The diagram on the right shows additive color mixing. In this case, the primary colors are red, green, and blue, and the secondary colors are cyan, magenta, and yellow. Mixing pigments and mixing light are different because materials absorb light by a different set of rules than does the perception of light by the eye. Notice that, when all colors are subtracted, the result is no color, or black. When all colors are added, the result is white light. We see the reverse of this when white sunlight is separated into the visible spectrum by a prism or by raindrops when a rainbow appears in the sky.

View original figure (external; image not reproduced in this text edition)

Original figure description: 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 “Pigment” at the top and “Subtractive color” at the bottom, has the three circles on a white background. The top circle is labeled “Y” and colored yellow; the bottom left circle is labeled “M” and colored magenta; the bottom right circle is labeled “C” and colored cyan. The areas of overlap of pairs of circles are colored red, dark blue, and green, and the area of overlap of all three circles is black. The right panel, labeled “Light” at the top and “Additive color” at the bottom, has the three circles on a black background. The top circle is labeled “R” and colored red; the bottom left circle is labeled “G” and colored green; the bottom right circle is labeled “B” and colored dark blue. The areas of overlap of pairs of circles are colored yellow, cyan, and magenta, and the area of overlap of all three circles is white.

Mixing colored pigments follows the subtractive color wheel, and mixing colored light follows the additive color wheel.

Animal Color Perception

The physics of color perception has interesting links to zoology. Other animals have very different views of the world than humans, especially with respect to which colors can be seen. Color is detected by cells in the eye called cones. Humans have three cones that are sensitive to three different ranges of electromagnetic wavelengths. They are called red, blue, and green cones, although these colors do not correspond exactly to the centers of the three ranges. The ranges of wavelengths that each cone detects are red, 500 to 700 nm; green, 450 to 630 nm; and blue, 400 to 500 nm.

Most primates also have three kinds of cones and see the world much as we do. Most mammals other than primates only have two cones and have a less colorful view of things. Dogs, for example see blue and yellow, but are color blind to red and green. You might think that simpler species, such as fish and insects, would have less sophisticated vision, but this is not the case. Many birds, reptiles, amphibians, and insects have four or five different cones in their eyes. These species don’t have a wider range of perceived colors, but they see more hues, or combinations of colors. Also, some animals, such as bees or rattlesnakes, see a range of colors that is as broad as ours, but shifted into the ultraviolet or infrared.

These differences in color perception are generally adaptations that help the animals survive. Colorful tropical birds and fish display some colors that are too subtle for us to see. These colors are believed to play a role in the species mating rituals. Figure_15_01_DogBee shows the colors visible and the color range of vision in humans, bees, and dogs.

View original figure (external; image not reproduced in this text edition)

Original figure description: This figure shows three parallel, horizontal bands of colors, labeled “Humans”, “Bees”, and “Dogs”. Each band starts with the blue color on the left and ends with the red color on the right. Above the bands is a horizontal line calibrated with numbers ranging from 300 on the left to 700 on the right, and the line is labeled as “Wavelength”, followed by the letters n m in parentheses.

Humans, bees, and dogs see colors differently. Dogs see fewer colors than humans, and bees see a different range of colors.

The belief that bulls are enraged by seeing the color red is a misconception. What did you read in this Links to Physics that shows why this belief is incorrect?

Bulls are color-blind to every color in the spectrum of colors.
Bulls are color-blind to the blue colors in the spectrum of colors.
Bulls are color-blind to the red colors in the spectrum of colors.
Bulls are color-blind to the green colors in the spectrum of colors.

Humans have found uses for every part of the electromagnetic spectrum. We will take a look at the uses of each range of frequencies, beginning with visible light. Most of our uses of visible light are obvious; without it our interaction with our surroundings would be much different. 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 have almost no oxygen in the atmosphere.

The low-frequency, infrared region of the spectrum has many applications in media broadcasting. Television, radio, cell phone, and remote-control 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, but that is not their basic difference. AM and FM are abbreviations for amplitude modulation and frequency modulation. Information in AM signals has the form of changes in amplitude of the radio waves; information in FM signals has the form of changes in wave frequency.

Another application of long-wavelength radiation is found in microwave ovens. These appliances cook or warm food by irradiating it with EM radiation in the microwave frequency range. Most kitchen microwaves use a frequency of $2.45 \times 10^{9}$ Hz. These waves have the right amount of energy to cause polar molecules, such as water, to rotate faster. Polar molecules are those that have a partial charge separation. The rotational energy of these molecules is given up to surrounding matter as heat. The first microwave ovens were called Radaranges because they were based on radar technology developed during World War II.

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

Exposure to any radiation with frequencies greater than those of visible light carries some health hazards. All types of radiation in this range are known to cause cell damage. The danger is related to the high energy and penetrating ability of these EM waves. The likelihood of being harmed by any of this radiation depends largely on the amount of exposure. Most people try to reduce exposure to UV radiation from sunlight by using sunscreen and protective clothing. Physicians still use X-rays to diagnose medical problems, but the intensity of the radiation used is extremely low. Figure_15_01_X-ray shows an X-ray image of a patient’s chest cavity.

One medical-imaging technique that involves no danger of exposure is magnetic resonance imaging (MRI). MRI is an important imaging and research tool in medicine, 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 hydrogen nuclei—protons.

View original figure (external; image not reproduced in this text edition)

Original figure description: 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.

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

Check Your Understanding

Identify the fields produced by a moving charged particle.

Both an electric field and a magnetic field will be produced.
Neither a magnetic field nor an electric field will be produced.
A magnetic field, but no electric field will be produced.
Only the electric field, but no magnetic field will be produced.

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Section Summary

The electromagnetic spectrum is made up of a broad range of frequencies of electromagnetic radiation.
All frequencies of EM radiation travel at the same speed in a vacuum and consist of an electric field and a magnetic field. The types of EM radiation have different frequencies and wavelengths, and different energies and penetrating ability.

Concept Items

Use the concepts on which Maxwell’s equations are based to explain why a compass needle is deflected when the compass is brought near a wire that is carrying an electric current.

The charges in the compass needle and the charges in the electric current have interacting electric fields, causing the needle to deflect.
The electric field from the moving charges in the current interacts with the magnetic field of the compass needle, causing the needle to deflect.
The magnetic field from the moving charges in the current interacts with the electric field of the compass needle, causing the needle to deflect.
The moving charges in the current produce a magnetic field that interacts with the compass needle’s magnetic field, causing the needle to deflect.

Consider these colors of light: yellow, blue, and red. Part A. Put these light waves in order according to wavelength, from shortest wavelength to longest wavelength. Part B. Put these light waves in order according to frequency, from lowest frequency to highest frequency.

wavelength: blue, yellow, red
frequency: blue, yellow, red
wavelength: red, yellow, blue
frequency: red, yellow, blue
wavelength: red, yellow, blue
frequency: blue, yellow, red
wavelength: blue, yellow, red
frequency: red, yellow, blue

Describe the location of gamma rays on the electromagnetic spectrum.

At the high-frequency and long-wavelength end of the spectrum
At the high-frequency and short-wavelength end of the spectrum
At the low-frequency and long-wavelength end of the spectrum
At the low-frequency and short-wavelength end of the spectrum

In which region of the electromagnetic spectrum would you find radiation that is invisible to the human eye and has low energy?

Long-wavelength and high-frequency region
Long-wavelength and low-frequency region
Short-wavelength and high-frequency region
Short-wavelength and low-frequency region

Critical Thinking

Standing in front of a fire, we can sense both its heat and its light. How are the light and heat radiated by the fire the same, and how are they different?

Both travel as waves, but only light waves are a form of electromagnetic radiation.
Heat and light are both forms of electromagnetic radiation, but light waves have higher frequencies.
Heat and light are both forms of electromagnetic radiation, but heat waves have higher frequencies.
Heat and light are both forms of electromagnetic radiation, but light waves have higher wavelengths.

Light shines on a picture of the subtractive color wheel. The light is a mixture of red, blue, and green light.
Part A—Which part of the color wheel will look blue? Explain in terms of absorbed and reflected light.
Part B—Which part of the color wheel will look yellow? Explain in terms of absorbed and reflected light.

1. The yellow section of the wheel will look blue because it will reflect blue light and absorb red and green.
2. The blue section of the wheel will look yellow because it will reflect red and green light and absorb blue.
1. The blue section of the wheel will look blue because it will absorb blue light and reflect red and green.
2. The yellow section of the wheel will look yellow because it will absorb red and green light and reflect blue.
1. The yellow section of the wheel will look blue because it will absorb blue light and reflect red and green.
2. The blue section of the wheel will look yellow because it will absorb red and green light and reflect blue.
1. The blue section of the wheel will look blue because it will reflect blue light and absorb red and green.
2. The yellow section of the wheel will look yellow because it will reflect red and green light and absorb blue.

Part A. When you stand in front of an open fire, you can sense light waves with your eyes. You sense another type of electromagnetic radiation as heat. What is this other type of radiation?
Part B. How is this other type of radiation different front light waves?

1. X-rays
2. The X-rays have higher frequencies and shorter wavelengths than the light waves.
1. X-rays
2. The X-rays have lower frequencies and longer wavelengths than the light waves.
1. infrared rays
2. The infrared rays have higher frequencies and shorter wavelengths than the light waves.
1. infrared rays
2. The infrared rays have lower frequencies and longer wavelengths than the light waves.

Overexposure to this range of EM radiation is dangerous, and yet it is used by doctors to diagnose medical problems.
Part AIdentify the type of radiation.
Part BLocate the position of this radiation on the EM spectrum by comparing its frequency and wavelength to visible light.
Part CExplain why this radiation is both dangerous and therapeutic in terms of its energy, based on your answer to Part B.

A. X-rays
B. X-rays have shorter wavelengths (1 × 10^–8 – 5 × 10^–12 m) and higher frequencies (3 × 10¹⁶ – 6 × 10¹⁹ Hz) than visible light (7.5 × 10^–7 – 4.0 × 10^–7 m; 4.0 × 10¹⁴ – 7.5 × 10¹⁴ Hz).
C. X-rays have low energies because of their high frequencies, and so can penetrate matter to greater depths.
A. X-rays
B. X-rays have shorter wavelengths (1 × 10^–8 – 5 × 10^–12 m) and higher frequencies (3 × 10¹⁰ – 6 × 10¹³ Hz) than visible light (7.5 × 10^–7 – 4.0 × 10^–7 m; 4.0 × 10¹⁴ – 7.5 × 10¹⁴ Hz).
C. X-rays have low energies because of their low frequencies, and so can penetrate matter to greater depths.
A. X-rays B. X-rays have longer wavelengths (1 × 10^–6 – 5 × 10^–7 m) and higher frequencies (3 × 10¹⁵ – 6 × 10¹⁵ Hz) than visible light (7.5 × 10^–7 – 4.0 × 10^–7 m; 4.0 × 10¹⁴ – 7.5 × 10¹⁴ Hz).
C. X-rays have high energies because of their high frequencies, and therefore can penetrate matter to greater depths.
A. X-rays
B. X-rays have shorter wavelengths (1 × 10^–8 – 5 × 10^–12 m) and higher frequencies (3 × 10¹⁶ – 6 × 10¹⁹ Hz) than visible light (7.5 × 10^–7 – 4.0 × 10^–7 m; 4.0 × 10¹⁴ – 7.5 × 10¹⁴ Hz).
C. X-rays have high energies because of their high frequencies, and so can penetrate matter to greater depths.

Test Prep Multiple Choice

Which type of EM radiation has the shortest wavelengths?

gamma rays
infrared waves
blue light
microwaves

Which form of EM radiation has the most penetrating ability?

red light
microwaves
gamma rays
infrared radiation

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Test Prep Short Answer

Describe one way in which heat waves—infrared radiation—are different from sound waves.

Sound waves are transverse waves, whereas heat waves—infrared radiation—are longitudinal waves.
Sound waves have shorter wavelengths than heat waves.
Sound waves require a medium, whereas heat waves—infrared radiation—do not.
Sound waves have higher frequencies than heat waves.

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Test Prep Extended Response

A frequency of red light has a wavelength of 700 nm.
Part A—Compare the wavelength and frequency of violet light to red light.
Part B—Identify a type of radiation that has lower frequencies than red light.
Part C—Identify a type of radiation that has shorter wavelengths than violet light.

1. Violet light has a lower frequency and longer wavelength than red light.
2. ultraviolet radiation
3. infrared radiation
1. Violet light has a lower frequency and longer wavelength than red light.
2. infrared radiation
3. ultraviolet radiation
1. Violet light has a higher frequency and shorter wavelength than red light.
2. ultraviolet radiation
3. infrared radiation
1. Violet light has a higher frequency and shorter wavelength than red light.
2. infrared radiation
3. ultraviolet radiation

A mixture of red and green light is shone on each of the subtractive colors.
Part A—Which of these colors of light are reflected from magenta?
Part B—Which of these colors of light are reflected from yellow?
Part C—Which these colors of light are reflected from cyan?

Part A. red and green
Part B. green
Part C. red
Part A. red and green
Part B. red
Part C. green
Part A. green
Part B. red and green
Part C. red
Part A. red
Part B. red and green
Part C. green

Glossary

electric field: a field that tells us the force per unit charge at all locations in space around a charge distribution
electromagnetic radiation (EMR): radiant energy that consists of oscillating electric and magnetic fields
magnetic field: the directional lines around a magnetic material that indicates the direction and magnitude of the magnetic force
Maxwell’s equations: equations that describe the interrelationship between electric and magnetic fields, and how these fields combine to form electromagnetic radiation

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