C12 Electromagnetic Waves

8/17/2019 C12 Electromagnetic Waves

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Electromagnetic

Waves


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What are electromagnetic waves?

How electromagnetic waves are formed

How electric charges produce

electromagnetic waves

Properties of electromagnetic waves


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Electromagnetic Waves…

Do not need matter to transfer energy.


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Electromagnetic Waves…

Do not need matter to transfer energy.

Are made by vibrating electric charges

and can travel through space by

transferring energy between vibrating

electric and magnetic fields.


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How do moving charges create

magnetic fields? Any moving electric charge is surrounded by an

electric field and a magnetic field.


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What happens when electric and

magnetic fields change? A changing magnetic field creates a

changing electric field.


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magnetic fields change? A changing magnetic field creates a

changing electric field.

ne e!ample of this is a transformer

which transfers electric energy from one

circuit to another circuit.


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magnetic fields change? A changing magnetic field creates a changing

electric field.

ne e!ample of this is a transformer whichtransfers electric energy from one circuit toanother circuit. "n the main coil changing electric current produces a

changing magnetic field

Which then creates a changing electric field inanother coil producing an electric current #he reverse is also true.


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This page was copied from Nick Strobel's Astronomy Notes. Go to

his site at www.astronomynotes.com for the updated and

corrected version.

http://www.astronomynotes.com/http://www.astronomynotes.com/http://www.astronomynotes.com/http://www.astronomynotes.com/


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$a%ing Electromagnetic Waves

When an electric charge vibrates& the electric

field around it changes creating a changing

magnetic field.


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#he magnetic and electric fields create each

other again and again.


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An E$ wave travels in all directions. #he figure

only shows a wave traveling in one direction.


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#he electric and magnetic fields vibrate at right

angles to the direction the wave travels so it is a

transverse wave.


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Properties of E$ Waves

All matter contains charged particles that

are always moving' therefore& all ob(ects

emit E$ waves.


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emit E$ waves. #he wavelengths become shorter as the

temperature of the material increases.


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emit E$ waves. #he wavelengths become shorter as the

temperature of the material increases.

E$ waves carry radiant energy.


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What is the speed of E$ waves?

All E$ waves travel

)**&*** %m+sec in

space. ,speed of light-natures limit/0


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What is the speed of E$ waves?

All E$ waves travel

)**&*** %m+sec in

space. ,speed of light-natures limit/0

E$ waves usually

travel slowest in

solids and fastest ingases.

$aterial 1peed,%m+s0

2acuum )**&***

Air 3)**&***

Water 445&***

6lass 4**&***

Diamond 748&***


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What is the wavelength 9

fre:uency of an E$ wave? Wavelength; distance from crest to crest.


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=an a wave be a particle?

"n 7>>& Heinrich Hert@ discovered that

shining light on a metal caused electrons

to be e(ected.


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"n 7>>& Heinrich Hert@ discovered that

shining light on a metal caused electrons

to be e(ected. Whether or not electrons were e(ected

depended upon frequency not the

amplitude of the light/ emember energydepends on amplitude.


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Bears later& Albert Einstein e!plained

Hert@s discoveryC E$ waves can behave

as a particle called a photon whoseenergy depends on the fre:uency of the

waves.


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=an a particle be a wave?

Electrons fired at two

slits actually form an

interference patternsimilar to patterns

made by waves


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=an a particle be a wave?

Electrons fired at two

slits actually form an

interference patternsimilar to patterns

made by waves


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Electromagnetic Waves

How they are formed ind of wave 1ometimes behave as


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Electromagnetic Waves

How they are formed

Waves made by

vibrating electric

charges that can

travel through space

where there is no

matter

ind of wave

#ransverse with

alternating electric

and magnetic fields

1ometimes behave as

Waves or as

Particles ,photons0


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Electromagnetic

Waves

1ection 4 #he

Electromagnetic 1pectrum


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#he whole range of E$ wave…


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As wavelength decreases&

fre:uency increases…


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Devices detect other fre:uenciesC

Antennae of a radio detects radio waves.


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Radio waves are low fre:uency E$

waves with wavelengths longer than 7mm.


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Radio waves are low fre:uency E$

waves with wavelengths longer than 7mm. #hese waves must be turned into sound

waves by a radio before you can hear

them.


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What are microwaves?

Microwaves are radio waves with

wavelengths less than )* cm and higher

fre:uency 9 shorter wavelength.


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Microwaves are radio waves with

wavelengths less than )* cm and higher

fre:uency 9 shorter wavelength. =ell phones and satellites use microwaves

between 7 cm 9 4* cm for

communication.


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Microwaves are radio waves with wavelengthsless than )* cm and higher fre:uency 9 shorterwavelength.

=ell phones and satellites use microwavesbetween 7 cm 9 4* cm for communication.

"n microwave ovens& a vibrating electric field

causes water molecules to rotate billions oftimes per second causing friction& creating #Ewhich heats the food.


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How does radar wor%?

Radio etecting And Ranging or radar is

used to find position and speed of ob(ects

by bouncing radio waves off the ob(ect.


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What is magnetic resonance

imaging? $" was developed in the 7>*s to use

radio waves to diagnose illnesses with a

strong magnet and a radio wave emitterand a receiver. Protons in H atoms of thebody act li%e magnets lining up with thefield. #his releases energy which the

receiver detects and creates a map of thebodys tissues.


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Infrared Waves

E$ with wavelengths between 7mm 9 F*billionths of a meter.

Gsed daily in remote controls& to read =D-$s

Every ob(ects gives off infrared waves'

hotter ob(ects give off more than coolerones. 1atellites can "D types of plantsgrowing in a region with infrared detectors


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Visible Light

ange of E$ humans can see from F*

billionths to 8** billionths of a meter.

Bou see different wavelengths as colors.lue has shortest

ed is the longest

Iight loo%s white if all colors are present


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A range of fre:uencies

"n order of increasing fre:uency anddecreasing wavelength& the E$spectrum consists ofC very longwave radio& used forcommunication with submarines'

long& medium and short waveradio ,used for A$ broadcasting0'


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Ultraviolet Waves

E$ waves with wavelengths from about

8** billionths to 7* billionths of a meter.

Have enough energy to enter s%in cellsIonger wavelengths J G2A

1horter wavelengths J G2 rays

oth can cause s%in cancer


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=an G2 radiation be useful?

Helps body ma%e vitamin D for healthy

bones and teeth

Gsed to sterili@e medical supplies 9 e:uip Detectives use fluorescent powder

,absorbs G2 9 glows0 to find fingerprints


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What is the o@one layer?

4*-F* %m above earth $olecule of ) atoms

Absorbs 1uns harmfulG2 rays @one layer

decreasing due to

=


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What could happen to humans…

And other life on Earth if the o@one layer is

destroyed?


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Rays and !amma Rays

E$ waves with

shortest wavelength 9

highest fre:uency High Energy- go

through s%in 9 muscle

High level e!posure

causes cancer


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Rays and !amma Rays

E$ with wavelengthsshorter than 7*trillionths of a meter.

Highest energy& cantravel through severalcentimeters of lead.

oth can be used inradiation therapy to%ill diseased cells.

#he composite imageshows the all s%ygamma ray

bac%ground.


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"dentify which statement is not trueC

A. 6amma rays are low fre:uency waves.

. K rays are high-energy waves.

=. 6amma rays are used to treat

diseases.


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Why do you thin% $"s cause ...

Iess harm than K rays?


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<


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Electromagnetic

Waves

=hp. 74 1ection ) adio

=ommunication


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adio #ransmission

adio stations

change sound to E$

waves 9 then your

radio receiver

changes the E$

waves bac% to sound

waves again.


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How does a radio receive different

stations? Each station broadcasts at a certain

fre:uency which you tune in by choosing

their fre:uency. "arrier wave- the fre:uency of the E$

wave that a station uses $icrophones convert sound waves to a

changing electric current or electronicsignal containing the words 9 music.


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stations? $icrophones convert sound waves to a

changing electric current or electronic

signal containing the words 9 music. #he modified carrier wave vibrates

electrons in the stations antennaecreating a radio wave that travels out in all

directions at the speed of light to yourradio antennae.


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stations? #he modified carrier wave vibrates electrons in

the stations antennae creating a radio wave that

travels out in all directions at the speed of light

to your radio antennae.

#he vibrating electrons produce a changing

electric current which your radio separates the

carrier wave from the signal to ma%e thespea%ers vibrate creating sound waves….


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What is A$ radio?

"n A$ amplitude changes but fre:uency doesnot. A$ fre:uencies range from F8*&*** H@

to 7&5***&*** H@ usually listed in %H@.


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What is


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#elevision

Gses radio waves to send electronic

signals in a carrier wave.

1ound is sent by


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What is a cathode-ray tube?

$any #2s and computer monitors display

images on a =#& a sealed vacuum tube

in which beams of electrons are produced. =olor #2 produces ) electron beams

inside the =# which stri%e the inside of

the screen that is covered with more than7**&*** rectangular spots.


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What is a cathode-ray tube?

#here are ) types of spots& red& green and

blue. #he electron beams move bac% and

forth across the screen. #he signal from the #2 station controls

how bright each spot is. #hree spots

together can form any color. Bou see a full color image on the #2.


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#elephones

1ound waves microphone electric signal

radio waves transmitted to and from

microwave tower receiver electric signal

spea%er sound wave

!obile "hone #TS ase #ransceiver 1tation #S$ ase 1tation

=ontroller !S$ $obile services 1witching =entre %&R 2isitor Iocation

egister &R Home Iocation egister


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How do cordless phones wor%?

=ell phones and cordless telephones are

transceivers# device that transmits one

signal 9 receives another radio signal froma base unit.

Bou can tal% and listen at the same time

because the two signals are at differentfre:uencies.


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How do pagers wor%?

A pager is a small radio receiver with aphone number. A caller leaves a message

at a terminal with a call-bac% number. At the terminal& the message is turned into

an electronic signal transmitted by radiowaves.

Lewer pagers can send and receivemessages.


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=ommunications 1atellites #housands of satellites

orbit Earth. A radio or

#2 station sends

microwave signals tothe satellite which

amplifies the signal and

sends it bac% to a

different place onEarth. 1atellite uses dif

fre: to send 9 receive.


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6lobal Positioning 1ystem

6P1 is a system of 48 satellites& ground

monitoring stations and portable receivers

that determine your e!act location on Earth.

6P1 receiver measures the time it ta%es forradio waves to travel from 8 different satellites

to the receiver. #he system is owned and

operated by the G1 Dept of Defense& but the

microwaves can be used by anyone.

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C12 Electromagnetic Waves