Electromagnetic Waves

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What is the electromagnetic

spectrum?The waves that carry voices to your cell phone are

electromagnetic waves. So are the waves of energy that toast your bread. Even the X-rays that a dentist uses to check the health of your teeth are electromagnetic waves.

The changing motion of an electric charge produces each type of electromagnetic wave. However, each type of wave has a different frequency and wavelength. Also, each carries a different amount of energy.

Electromagnetic waves might vibrate from a thousand times per second to trillions of times per second. They might be as large as a house or as small as an atom’s nucleus. The electromagnetic

spectrum is the entire range of electromagnetic waves with different frequencies and wavelengths.

Classifying Electromagnetic WavesThink about the colors of a rainbow. There are many shades

between each color. Each color gradually becomes another. However, the electromagnetic spectrum is organized into groups based on the wavelengths and frequencies of the waves. Like the colors of a rainbow, each group gradually blends into the next.

What do you think? Read the two statements below and decide

whether you agree or disagree with them. Place an A in the Before

column if you agree with the statement or a D if you disagree. After

you’ve read this lesson, reread the statements to see if you have

changed your mind.

Before Statement After

3. Red light has the least amount of energy of

all colors of light.

4. A television remote control emits radiation.

Key Concepts

• What is the

electromagnetic

spectrum?

• How do electromagnetic

waves differ?

Building Vocabulary Make

a vocabulary card for each

bold term in this lesson.

Write each term on one

side of the card. On the

other side, write the

definition. Use your cards

to review the vocabulary

for the lesson.

Key Concept

Check

1. Classify What is the

electromagnetic spectrum,

and how do

electromagnetic waves

differ?

Electromagnetic Waves

The Electromagnetic Spectrum

LESSON 2

The Electromagnetic Spectrum Electromagnetic Waves 459

CHAPTER 15

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Visual Check

2. Distinguish Which

types of electromagnetic

waves have wavelengths

that are too long for your

eyes to see?

Each numbered description below relates to a numbered wave in the figure above. Notice how the wavelength, frequency, and energy change among waves.

1. A radio wave is a low-frequency, low-energy electromagnetic wave that has a wavelength longer than about 30 cm. Some radio waves have wavelengths as long as a kilometer or more. Radio waves are often used for communication. The wavelengths are long enough to move around many objects, but their energy is low enough that they aren’t harmful. On Earth, radio waves are usually produced by an electric charge moving in an antenna. However, the Sun and other objects in space also produce radio waves.

2. A microwave is a low-frequency, low-energy electromagnetic wave that has a wavelength between about 1 mm and 30 cm. Like radio waves, microwaves are often used for communication. With shorter wavelengths than radio waves, microwaves are less often scattered by particles in the air. Microwaves are useful for satellite communications because they can pass through Earth’s upper atmosphere. A cell phone uses microwaves from satellites. Because of the frequency range of microwaves, food molecules such as water and sugar can absorb their energy. This makes microwaves useful for cooking.

3. An infrared wave is an electromagnetic wave that has a wavelength shorter than a microwave but longer than light. Vibrating molecules in any matter, including your body, emit infrared waves. You cannot see infrared waves, but you can feel them when you are near a campfire. Your skin senses infrared waves with longer wavelengths as warmth. Infrared waves with shorter wavelengths do not feel warm. A television remote control, for example, sends out these waves.

Reading Check

3. Explain How do

microwaves cook food?

Electromagnetic Spectrum

Make an eight-layer book

to compare and contrast

the different types of

electromagnetic waves.

460 Electromagnetic Waves The Electromagnetic Spectrum


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4. Light is electromagnetic waves that your eyes can see. You might describe light as red, orange, yellow, green, blue, indigo, and violet. Red light has the longest wavelength and lowest frequency. Violet light has the shortest wavelength and the highest frequency. Each name represents a family of colors, each with a range of wavelengths.

5. An ultraviolet wave is an electromagnetic wave that has a slightly shorter wavelength and higher frequency than light, and carries enough energy to cause chemical reactions. Earth’s atmosphere prevents most of the Sun’s ultraviolet rays from reaching Earth. But did you know that you can get a sunburn on a cloudy day? This is because ultraviolet waves carry enough energy to move through clouds and to penetrate the skin. They can damage or kill cells, causing sunburn or even skin cancer.

6. An X-ray is a high-energy electromagnetic wave that has a slightly shorter wavelength and higher frequency than an ultraviolet wave. Have you ever had an X-ray taken to see if you had a broken bone? X-rays have enough energy to pass through skin and muscle. But the calcium in bone can stop them. Scientists learn about objects and events in space, such as black holes and star explosions, by studying the X-rays they emit.

7. A gamma ray is a high-energy electromagnetic wave with a shorter wavelength and higher frequency than all other types of electromagnetic waves. Gamma rays are produced when the nucleus of an atom breaks apart. They have enough energy to kill living cells. Like X-rays, gamma rays form in space during violent events, such as the explosion of stars.

4. Apply On a cloudy day

at the beach, do you need

to wear sunscreen? Why or

why not?

Reading Check

5. Explain What creates

the high energy in a

gamma ray?

The Electromagnetic Spectrum Electromagnetic Waves 461


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Mini Glossary

electromagnetic spectrum: the entire range of electromagnetic waves with different frequencies and wavelengths

gamma ray: a high-energy electromagnetic wave with a shorter wavelength and higher frequency than all other types of electromagnetic waves

infrared wave: an electromagnetic wave that has a wavelength shorter than a microwave but longer than light

microwave: a low-frequency, low-energy electromagnetic wave that has a wavelength between about 1 mm and 30 cm

radio wave: a low-frequency, low-energy electromagnetic wave that has a wavelength longer than about 30 cm

ultraviolet wave: an electromagnetic wave that has a slightly shorter wavelength and higher frequency than light, and carries enough energy to cause chemical reactions

X-ray: a high-energy electromagnetic wave that has a slightly shorter wavelength and higher frequency than an ultraviolet wave

1. Review the terms and their definitions in the Mini Glossary. Write a sentence that describes a way that X-rays benefit people.

2. A wave’s wavelength, frequency, and energy are related. In the table, one factor is provided for waves B and C. Write the other two factors for waves B and C. Use the figure in this lesson to help you. Follow wave A as an example. Wave A shows that if frequency is higher, then energy also is higher, but wavelength is shorter.

Relationship Between Wavelength, Frequency, and Energy

Wavelength

(longer or shorter)

Frequency

(higher or lower)

Energy

(higher or lower)

Wave A shorter higher higher

Wave B longer

Wave C higher

Reread the statements at the beginning of the

lesson. Fill in the After column with an A if you

agree with the statement or a D if you dis-

agree. Did you change your mind?

What do you think

END OF LESSON

Log on to ConnectED.mcgraw-hill.com and access your textbook to find this lesson’s resources.

462 Electromagnetic Waves The Electromagnetic Spectrum


Electromagnetic Waves 463

Lesson 2

Predict three facts that will be discussed in Lesson 2 after reading the headings. Write your facts in your Science Journal.

The Electromagnetic SpectrumC

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ight

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Generalize the reason for the range of energy carried by waves in the electromagnetic spectrum.

Each wave has a different and

, so

.

Define the electromagnetic spectrum.

Characterize the electromagnetic spectr um.

Ty

pe

of

Wa

ve

wavelength

frequency

energy

Diagram:

wavelength

frequency

energy

What is the

electromagnetic

spectrum?

I found this on page .


Classifying

Electromagnetic Waves


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464 Electromagnetic Waves

Lesson 2 | The Electromagnetic Spectrum (continued)

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Differentiate wavelengths in the electromagnetic spectrum. The numbers in the boxes correspond to the art of the electromagnetic spectrum shown in your book.

A. Identify the type of wave.

B. Describe the wave’s

wavelength, frequency, and

energy.

C. Determine a use or

characteristic of the wave.

1

A. Radio wave

B.

C.

2

A.

B.

C.

3

A.

B.

C.

4

A.

B.

C.

5

A. Ultraviolet wave

B.

C.

6

A. X-ray

B.

C.

7

A.

B.

C.


Envision a quick look around your home. Explain which type of electromagnetic wave you think is most useful to your lifestyle and why.


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Electromagnetic Waves

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