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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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Page 1: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

What are electromagnetic waves?

• How electromagnetic waves are formed• How electric charges produce

electromagnetic waves• Properties of electromagnetic waves

Page 2: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Electromagnetic Waves…

• Do not need matter to transfer energy.

Page 3: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

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.

Page 4: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

How do moving charges create magnetic fields?

• Any moving electric charge is surrounded by an electric field and a magnetic field.

Page 5: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

What happens when electric and magnetic fields change?

• A changing magnetic field creates a changing electric field.

Page 6: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

What happens when electric and magnetic fields change?

• A changing magnetic field creates a changing electric field.

• One example of this is a transformer which transfers electric energy from one circuit to another circuit.

Page 7: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

What happens when electric and magnetic fields change?

• A changing magnetic field creates a changing electric field.

• One example of this is a transformer which transfers electric energy from one circuit to another circuit.– In the main coil changing electric current produces a

changing magnetic field– Which then creates a changing electric field in

another coil producing an electric current– The reverse is also true.

Page 8: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

This page was copied from Nick Strobel's Astronomy Notes. Go to his site at www.astronomynotes.com for the updated and

corrected version.

Page 9: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Making Electromagnetic Waves

• When an electric charge vibrates, the electric field around it changes creating a changing magnetic field.

Page 10: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Making Electromagnetic Waves

• The magnetic and electric fields create each other again and again.

Page 11: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Making Electromagnetic Waves

• An EM wave travels in all directions. The figure only shows a wave traveling in one direction.

Page 12: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Making Electromagnetic Waves

• The electric and magnetic fields vibrate at right angles to the direction the wave travels so it is a transverse wave.

Page 13: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Properties of EM Waves

• All matter contains charged particles that are always moving; therefore, all objects emit EM waves.

Page 14: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Properties of EM Waves

• All matter contains charged particles that are always moving; therefore, all objects emit EM waves.

• The wavelengths become shorter as the temperature of the material increases.

Page 15: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Properties of EM Waves

• All matter contains charged particles that are always moving; therefore, all objects emit EM waves.

• The wavelengths become shorter as the temperature of the material increases.

• EM waves carry radiant energy.

Page 16: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

What is the speed of EM waves?

• All EM waves travel 300,000 km/sec in space. (speed of light-nature’s limit!)

Page 17: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

What is the speed of EM waves?

• All EM waves travel 300,000 km/sec in space. (speed of light-nature’s limit!)

• EM waves usually travel slowest in solids and fastest in gases.

Material Speed (km/s)

Vacuum 300,000

Air <300,000

Water 226,000

Glass 200,000

Diamond 124,000

Page 18: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

What is the wavelength & frequency of an EM wave?

• Wavelength= distance from crest to crest.

Page 19: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

What is the wavelength & frequency of an EM wave?

• Wavelength= distance from crest to crest.• Frequency= number of wavelengths that

pass a given point in 1 s.

Page 20: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

What is the wavelength & frequency of an EM wave?

• Wavelength= distance from crest to crest.• Frequency= number of wavelengths that

pass a given point in 1 s.• As frequency increases, wavelength

becomes….

Page 21: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

What is the wavelength & frequency of an EM wave?

• Wavelength= distance from crest to crest.• Frequency= number of wavelengths that

pass a given point in 1 s.• As frequency increases, wavelength

becomes smaller.

Page 22: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Can a wave be a particle?

• In 1887, Heinrich Hertz discovered that shining light on a metal caused electrons to be ejected.

Page 23: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Can a wave be a particle?

• In 1887, Heinrich Hertz discovered that shining light on a metal caused electrons to be ejected.

• Whether or not electrons were ejected depended upon frequency not the amplitude of the light! Remember energy depends on amplitude.

Page 24: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Can a wave be a particle?

• Years later, Albert Einstein explained Hertz’s discovery: EM waves can behave as a particle called a photon whose energy depends on the frequency of the waves.

Page 25: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Can a particle be a wave?

• Electrons fired at two slits actually form an interference pattern similar to patterns made by waves

Page 26: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Can a particle be a wave?

• Electrons fired at two slits actually form an interference pattern similar to patterns made by waves

Page 27: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

The whole range of EM wave…

• Frequencies is called the electromagnetic spectrum.

Page 28: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

The whole range of EM wave…

• Frequencies is called the electromagnetic spectrum.

• Different parts interact with matter in different ways.

Page 29: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

The whole range of EM wave…

• Frequencies is called the electromagnetic spectrum.

• Different parts interact with matter in different ways.

• The ones humans can see are called visible light, a small part of the whole spectrum.

Page 30: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

How can we explain the Electromagnetic waves &

Spectrum?

Do Now:

A light wave in a vacuum is traveling with a frequency of 6.2 x 1010 Hz. What is the wavelength?

v = fλ

3.0 x 108 m/s = (6.2 x 1010 Hz)λ

λ = 4.8 x 10-3 m

Page 31: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

The Electromagnetic Spectrum

• The speed of all waves of the EM spectrum in a vacuum is the speed of light (c).

= 3.00 x 108 m/s

Page 32: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Light is an electromagnetic wave.

Visible light is only a small section of the electromagnetic spectrum.

The electromagnetic spectrum stretches from radio waves (low frequency, long wavelength) to gamma rays (high frequency, short wavelength)

Page 33: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Electromagnetic Radiation does not need a medium to propagate!

• Speed of light in vacuum, c = 3.0 x 108 m/s

Page 34: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Electromagnetic Radiation does not need a medium to propagate!

• Speed of light in vacuum, c = 3.0 x 108 m/s

• Light slows down when it passes through matter

Page 35: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Electromagnetic Radiation does not need a medium to propagate!

• Speed of light in vacuum, c = 3.0 x 108 m/s

• Light slows down when it passes through matter

• Dense materials tend to slow light down more

Page 36: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Electromagnetic Radiation does not need a medium to propagate!

• Speed of light in vacuum, c = 3.0 x 108 m/s

• Light slows down when it passes through matter

• Dense materials tend to slow light down more

• All electromagnetic waves obey the wave equation:

v = fλ

Page 37: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Use v = f λ to complete the following tableIn each case, use c (3.0 x 108 m/s) as the velocity

Type of wave Typical frequency (Hz)

Corresponding wavelength (m)

AM radio (LW) 1024

FM radio

Microwave 0.03

Infra-red 2 x 10-6

visible 600 x 10-9

Ultraviolet 200 x 10-9

X-ray & gamma 2.0 x 1018

Page 38: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Use v = f λ to complete the following tableIn each case, use c (3.0 x 108 m/s) as the velocity

Type of wave Typical frequency (Hz)

Corresponding wavelength (m)

AM radio (LW) 1024

FM radio 89.5 x 106 3.35

Microwave 0.03

Infra-red 2 x 10-6

visible 600 x 10-9

Ultraviolet 200 x 10-9

X-ray & gamma 2.0 x 1018

Page 39: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Use v = f λ to complete the following tableIn each case, use c (3.0 x 108 m/s) as the velocity

Type of wave Typical frequency (Hz)

Corresponding wavelength (m)

AM radio (LW) 293 x 106 1024

FM radio 89.5 x 106 3.35

Microwave 10.0 x 109 0.03

Infra-red 150 x 1012 2 x 10-6

visible 500 x 1012 600 x 10-9

Ultraviolet 1.5 x 1015 200 x 10-9

X-ray & gamma 2.0 x 1018 150 x 10-12

Page 40: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

When a wave passes from one medium to another

• The frequency stays the same.

• The speed of the wave may change.

• If so, the wavelength will change also.

• The wave will ALWAYS obey v = fλ

• The path of the wave may be bent…..

Page 41: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.
Page 42: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.
Page 43: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

• What type of wave has the longest wavelength?

• What type of wave has the shortest wavelength?

Page 44: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

• What type of wave has the longest wavelength?

• What type of wave has the shortest wavelength?

Long Radio Waves

Gamma Rays

Page 45: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

•About what is the wavelength of visible light?

Page 46: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

•About what is the wavelength of visible light?

10-7 m

Page 47: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

•What type of wave has the highest frequency?

•What type of wave has the lowest frequency?

Page 48: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

•What type of wave has the highest frequency?

•What type of wave has the lowest frequency?

Gamma Rays

Long Radio Waves

Page 49: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Visible light only makes up about 2% of the EM spectrum!

Page 50: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

• What color light has a frequency between 6.10 x 1014 Hz and 5.20 x 1014 Hz?

• What color light has a frequency between 5.03 x 1014

Hz and 4.82 x 1014 Hz?

GREEN

ORANGE

Page 51: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

In a vacuum, a monochromatic beam of light has a frequency of 6.3 x 1014 Hz. What color is the light?

BLUE

Page 52: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Finding Frequency or Wavelength of an Electromagnetic Wave

• Use the equation

v = fλ• Just remember that any EM wave has a

velocity of….

3.00 x 108 m/s

Hence, c = fλ

Page 53: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Determine the color of a ray of light with a

wavelength of 6.21 x 10-7 m.

c = fλ

(3.00 x 108 m/s) = f(6.21 x 10-7 m)

f = 4.83 x 1014 Hz

(ORANGE)

Page 54: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

•When asked to refer to a specific color’s frequency, choose the value to the LEFT of that color!

Page 55: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

What is the wavelength of red light?

c = fλ

3 x 108 m/s = (4.82 x 1014 Hz) λ

λ = 6.2 x 10-7 m

Page 56: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Calculate the wavelength of WPLJ (95.5 fm)

c = fλ

Hint: fm radio transmits in megahertz

(3.00 x 108 m/s) = (95.5 x 106 Hz) λ

λ = 3.14 m

Page 57: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

In a vacuum, all electromagnetic waves

have the same(1)Wavelength

(2)Frequency

(3)Speed

(4)amplitude

Page 58: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

A 2.00 x 106 Hz radio signal is sent a distance of 7.30 x 1010 meters from Earth to a spaceship orbiting Mars. Approximately how much time does it take the radio signal to travel from

Earth to the spaceship?(1)4.11 x 10-3 s(2)2.43 x 102 s(3)2.19 x 108 s(4)1.46 x 1017 s

t

dv

t

mxx

108 103.7

103

Page 59: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

How long does it take light to travel from the Sun to the Earth?

t

dv

t

mxx

118 105.1

103

st 500

st 20min8

Page 60: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

As wavelength decreases, frequency increases…

Page 61: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Devices detect other frequencies:

• Antennae of a radio detects radio waves.

Page 62: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Devices detect other frequencies:

• Antennae of a radio detects radio waves.• Radio waves are low frequency EM

waves with wavelengths longer than 1mm.

Page 63: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Devices detect other frequencies:

• Antennae of a radio detects radio waves.• Radio waves are low frequency EM

waves with wavelengths longer than 1mm.• These waves must be turned into sound

waves by a radio before you can hear them.

Page 64: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

What are microwaves?

• Microwaves are radio waves with wavelengths less than 30 cm and higher frequency & shorter wavelength.

Page 65: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

What are microwaves?

• Microwaves are radio waves with wavelengths less than 30 cm and higher frequency & shorter wavelength.

• Cell phones and satellites use microwaves between 1 cm & 20 cm for communication.

Page 66: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

What are microwaves?

• Microwaves are radio waves with wavelengths less than 30 cm and higher frequency & shorter wavelength.

• Cell phones and satellites use microwaves between 1 cm & 20 cm for communication.

• In microwave ovens, a vibrating electric field causes water molecules to rotate billions of times per second causing friction, creating TE which heats the food.

Page 67: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

How does radar work?

• Radio Detecting And Ranging or radar is used to find position and speed of objects by bouncing radio waves off the object.

Page 68: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

What is magnetic resonance imaging?

• MRI was developed in the 1980s to use radio waves to diagnose illnesses with a strong magnet and a radio wave emitter and a receiver. Protons in H atoms of the body act like magnets lining up with the field. This releases energy which the receiver detects and creates a map of the body’s tissues.

Page 69: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Infrared Waves

• EM with wavelengths between 1mm & 750 billionths of a meter.

• Used daily in remote controls, to read CD-ROMs

• Every objects gives off infrared waves; hotter objects give off more than cooler ones. Satellites can ID types of plants growing in a region with infrared detectors

Page 70: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Visible Light

• Range of EM humans can see from 750 billionths to 00 billionths of a meter.

• You see different wavelengths as colors.– Blue has shortest– Red is the longest– Light looks white if all colors are present

Page 71: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

A range of frequencies

In order of increasing frequency and decreasing wavelength, the EM spectrum consists of: very long wave radio, used for communication with submarines; long, medium and short wave radio (used for AM broadcasting); FM radio, television and radar; infra-red (heat) radiation, which is recorded in the Earth photographs taken by survey satellites; visible light; ultraviolet light, which, while invisible, stimulates fluorescence in some materials; x rays & gamma rays used in medicine and released in radioactive decay

Page 72: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Ultraviolet Waves

• EM waves with wavelengths from about 400 billionths to 10 billionths of a meter.

• Have enough energy to enter skin cells– Longer wavelengths – UVA– Shorter wavelengths – UVB rays– Both can cause skin cancer

Page 73: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Can UV radiation be useful?

• Helps body make vitamin D for healthy bones and teeth

• Used to sterilize medical supplies & equip• Detectives use fluorescent powder

(absorbs UV & glows) to find fingerprints

Page 74: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.
Page 75: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

What is the ozone layer?

• 20-50 km above earth• Molecule of 3 O atoms• Absorbs Sun’s harmful

UV rays• Ozone layer

decreasing due to CFCs in AC, refrigerators, & cleaning fluids

Page 76: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

What could happen to humans…

• And other life on Earth if the ozone layer is destroyed?

Page 77: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

X Rays and Gamma Rays

• EM waves with shortest wavelength & highest frequency

• High Energy- go through skin & muscle

• High level exposure causes cancer

Page 78: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

X Rays and Gamma Rays

• EM with wavelengths shorter than 10 trillionths of a meter.

• Highest energy, can travel through several centimeters of lead.

• Both can be used in radiation therapy to kill diseased cells.

• The composite image shows the all sky gamma ray background.

Page 79: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Identify which statement is not true:

• A. Gamma rays are low frequency waves.• B. X rays are high-energy waves.• C. Gamma rays are used to treat

diseases.

Page 80: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Why do you think MRIs cause ...

• Less harm than X rays?

Page 81: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

FFill in the boxes with the waves of the EM spectrum.

Page 82: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.
Page 83: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.
Page 84: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Electromagnetic Waves

Chp. 12 Section 3 Radio Communication

Page 85: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Radio Transmission

• Radio stations change sound to EM waves & then your radio receiver changes the EM waves back to sound waves again.

Page 86: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

How does a radio receive different stations?

• Each station broadcasts at a certain frequency which you tune in by choosing their frequency.

• Carrier wave- the frequency of the EM wave that a station uses

• Microphones convert sound waves to a changing electric current or electronic signal containing the words & music.

Page 87: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

How does a radio receive different stations?

• Microphones convert sound waves to a changing electric current or electronic signal containing the words & music.

• The modified carrier wave vibrates electrons in the station’s antennae creating a radio wave that travels out in all directions at the speed of light to your radio antennae.

Page 88: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

How does a radio receive different stations?

• The modified carrier wave vibrates electrons in the station’s antennae creating a radio wave that travels out in all directions at the speed of light to your radio antennae.

• The vibrating electrons produce a changing electric current which your radio separates the carrier wave from the signal to make the speakers vibrate creating sound waves….

Page 89: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

What is AM radio?

In AM amplitude changes but frequency does not. AM frequencies range from 540,000 Hz to 1,6000,000 Hz usually listed in kHz.

Page 90: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

What is FM radio?

• In FM radio stations transmit broadcast information by changing the frequency of the carrier wave. The strength of FM waves is always the same and is in megahertz. Mega=million

Page 91: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Television

• Uses radio waves to send electronic signals in a carrier wave.

• Sound is sent by FM; color and brightness is sent at the same time by AM signals.

Page 92: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

What is a cathode-ray tube?

• Many TVs and computer monitors display images on a CRT, a sealed vacuum tube in which beams of electrons are produced.

• Color TV produces 3 electron beams inside the CRT which strike the inside of the screen that is covered with more than 100,000 rectangular spots.

Page 93: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

What is a cathode-ray tube?

• There are 3 types of spots, red, green and blue. The electron beams move back and forth across the screen.

• The signal from the TV station controls how bright each spot is. Three spots together can form any color.

• You see a full color image on the TV.

Page 94: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Telephones

• Sound waves microphone electric signal radio waves transmitted to and from microwave tower receiver electric signal speaker sound wave

Mobile Phone BTS Base Transceiver Station BSC Base Station Controller

MSC Mobile services Switching Centre VLR Visitor Location Register HLR

Home Location Register

Page 95: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

How do cordless phones work?

• Cell phones and cordless telephones are transceivers, device that transmits one signal & receives another radio signal from a base unit.

• You can talk and listen at the same time because the two signals are at different frequencies.

Page 96: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

How do pagers work?

• A pager is a small radio receiver with a phone number. A caller leaves a message at a terminal with a call-back number.

• At the terminal, the message is turned into an electronic signal transmitted by radio waves.

• Newer pagers can send and receive messages.

Page 97: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Communications Satellites• Thousands of satellites

orbit Earth. A radio or TV station sends microwave signals to the satellite which amplifies the signal and sends it back to a different place on Earth. Satellite uses dif freq to send & receive.

Page 98: What are electromagnetic waves? How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves.

Global Positioning System

• GPS is a system of 24 satellites, ground monitoring stations and portable receivers that determine your exact location on Earth. GPS receiver measures the time it takes for radio waves to travel from 4 different satellites to the receiver. The system is owned and operated by the US Dept of Defense, but the microwaves can be used by anyone.


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