the electromagnetic spectrum the nature of electromagnetic waves waves of the electromagnetic...

The Electromagnetic Spectrum

The Nature of Electromagnetic Waves

Waves of the Electromagnetic Spectrum

Producing Visible Light

Wireless Communication

Table of Contents

The Electromagnetic Spectrum The Nature of Electromagnetic Waves

Electromagnetic Waves

Believe it or not, you are being “showered” all the time, not by rain but by waves.


Important Scientific Discoveries

James Clerk Maxwell first formally postulated electromagnetic waves. These were subsequently confirmed by Heinrich Hertz. Maxwell derived a wave form of the electric and magnetic equations, thus uncovering the wave-like nature of electric and magnetic fields, and their symmetry. Because the speed of EM waves predicted by the wave equation coincided with the measured speed of light, Maxwell concluded that light itself is an EM wave.

According to Maxwell's equations, a time-varying electric field generates a time-varying magnetic field and vice versa. Therefore, as an oscillating electric field generates an oscillating magnetic field, the magnetic field in turn generates an oscillating electric field, and so on. These oscillating fields together form a propagating electromagnetic wave.


What are Electromagnetic Waves?

Electromagnetic waves are transverse waves that transfer both electrical and magnetic energy.

All electromagnetic waves consist of vibrating electric and magnetic fields that move through space at the speed of light (3.0 x 10^8 m/s)


Producing Electromagnetic Waves

Light is an electromagnetic wave

All electromagnetic waves are produced by charged particles

Protons are positively charged (+)Electrons are negatively charged (-)

The electronic field produces electronic forces that push or pull on other charged particles.


Producing A Magnetic FieldA magnetic field is produced when a charged particle moves.The energy that is transferred through space by electromagnetic waves is called electromagnetic radiationElectromagnetic waves do not require a medium and therefore can travel through empty space (vacuum).


What Is an Electromagnetic Wave?

An electromagnetic wave consists of vibrating electric and magnetic fields that move through space at the speed of light.

An electromagnetic wave is a transverse wave that transfers electrical and magnetic energy.


Models of Electromagnetic Waves

Many properties of electromagnetic waves can be explained by a wave model. Only some light waves pass through a polarizing filter. The light that passes through vibrates in only one direction and is called polarized light.


Electromagnetic Wave ModelsSometimes light behaves like a stream of particles of energy. When a beam of light shines on some substances, it causes tiny particles called electrons to move and produce an electric current. Sometimes a beam of light can even cause electrons to be knocked out of substances. This is called the photoelectric effect. It can be explained only by thinking of light as a stream of tiny packets of energy. Each packet of light energy is called a photon.


OutliningAn outline shows the relationship between main ideas and supporting ideas. As you read, make an outline about electromagnetic waves. Use the red headings for the main ideas and the blue headings for the supporting ideas.



I. What Is an Electromagnetic Wave?A. Producing Electromagnetic

WavesB. EnergyC. Speed

II. Models of Electromagnetic WavesA. Wave Model of LightB. Particle Model of Light



Click the Video button to watch a movie about electromagnetic waves.



Links on the Nature of Waves

Click the SciLinks button for links on the nature of waves.


http://www.scilinks.org/fromoutside.asp?sciLINKSNumber=scn-1531&type=student


End of Section:The Nature of


The Electromagnetic Spectrum Waves of the Electromagnetic Spectrum

What Is the Electromagnetic Spectrum?

The electromagnetic spectrum is the complete range of electromagnetic waves placed in order of increasing frequency.


All electromagnetic waves travel at the same speed in a vacuum, but they have different wavelengths and different frequencies.

Recall: speed = wavelength x frequency


Scientific NotationFrequencies of waves often are written in scientific notation. A number in scientific notation consists of a number between 1 and 10 that is multiplied by a power of 10. To write 150,000 Hz in scientific notation, move the decimal point left to make a number between 1 and 10:

In this case, the number is 1.5. The power of 10 is the number of spaces you moved the decimal point. In this case, it moved 5 places:

150,000 Hz = 1.5 X 105 Hz



Scientific Notation

Practice Problem

A radio wave has a frequency of 5,000,000 Hz. Write this number in scientific notation.

5.0 X 106 Hz




Electromagnetic waves are all around you–in your home, your neighborhood, and your town.



Electromagnetic Waves Activity

Click the Active Art button to open a browser window and access Active Art about electromagnetic waves.



Previewing VisualsBefore you read, preview Figure 3. Then write two questions that you have about the diagram in a graphic organizer like the one below. As you read, answer your questions.


Q. Which electromagnetic waves have the shortest wavelength?

A. Gamma rays have the shortest wavelength.

Q. Which electromagnetic waves have the lowest frequency?

A. Radio waves have the lowest frequency.



Electromagnetic Spectrum

Click the Video button to watch a movie aboutthe electromagnetic spectrum.



End of Section:Waves of the

Electromagnetic Spectrum

The Electromagnetic Spectrum ProducingVisible Light

Incandescent Lights

An incandescent light is a light bulb that glows when a filament inside it gets white hot.

The Electromagnetic Spectrum ProducingVisible Light

Neon Lights

A neon light is a sealed glass tube that contains neon gas.


Feature

Comparing and ContrastingAs you read, compare and contrast the five types of light bulbs by completing a table like the one below.

Glass

Ordinary Light Bulb

Tungsten-Halogen

Fluorescent Vapor Neon

Bulb Material

Hot/Cool

Makeup

Efficiency

Quartz Glass Glass

Hot Very Hot Cool

Tungsten filament and nitrogen gas and argon gas inside

Has tungsten filament and a halogen gas inside

A gas and a powder coating inside

Has neon or argon gas and solid sodium or mercury inside

Has neon gas inside

Not efficient More efficient than ordinary bulb

Very efficient Very efficient

ProducingVisible Light

Glass

Cool Cool

Very efficient


Data Sharing Lab

Click the PHSchool.com button for an activity about sharing data for the Consumer Lab Comparing Light Bulbs.

ProducingVisible Light

http://phschool.com/webcodes10/index.cfm?fuseaction=home.gotoWebCode&wcprefix=cgd&wcsuffix=5033


End of Section:Producing

Visible Light

The Electromagnetic Spectrum WirelessCommunication

Radio and Television

In AM transmissions, the amplitude of a radio wave is changed. In FM transmissions, the frequency is changed.


Comparing Frequencies

The table shows the ranges of radio broadcast frequencies used for AM radio, UHF television, FM radio, and VHF television.

WirelessCommunication



Kilohertz (kHz) and megahertz (MHz)

Interpreting Data:

In the table, what units of measurement are used for frequency?




UHF television uses the highest frequency radio waves, and AM radio broadcast uses the lowest frequency radio waves.

Interpreting Data:

Which type of broadcast shown in the table uses the highest frequency radio waves? Which uses the lowest frequency waves?




UHF television uses waves with the highest frequency and therefore the shortest wavelength.

Calculating:

Which type of broadcast uses waves with the shortest wavelength?




You cannot tell from this data if it is a television or radio program, because VHF television and FM radio both broadcast radio waves with a frequency of 100 MHz.

Inferring:

A broadcast uses a frequency of 100 MHz. Can you tell from this data if it is a television or radio program? Explain.



Cellular Phone System

In the cellular phone system, cellular phones transmit and receive radio waves that travel to the nearest tower.


Communication Satellites

In the Global Positioning System (GPS), signals from four satellites are used to pinpoint a location on Earth.


What You Know

What You Learned

Using Prior KnowledgeYour prior knowledge is what you know before you read about a topic. Before you read, write what you know about wireless communication in a graphic organizer like the one below. As you read, continue to write what you learn.

1. Cellular phones don’t use wires.2. Radio and television signals travel through the air.

1. The signals for radio and television programs are carried by radio waves.

2. The signals can be transmitted by changing either the amplitude or the frequency of the radio waves.

3. Cellular phones transmit and receive signals using microwaves.



Links on Using Waves to Communicate

Click the SciLinks button for links onusing waves to communicate.


http://www.scilinks.org/fromoutside.asp?sciLINKSNumber=scn-1534&type=student


End of Section:Wireless

Communication


Graphic Organizer

Magnetic fields

Electromagnetic waves

consist of travel at the speed of

have different

Electric fields Wavelengths

Light

Frequencies


End of Section:Graphic Organizer

the electromagnetic spectrum the nature of electromagnetic waves waves of the electromagnetic...

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electromagnetic waves

light waves

transverse waves

speed of em waves

oscillating magnetic

magnetic fields

magnetic energy

oscillating electric