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The Nature of Electromagnetic WavesThe Nature of Electromagnetic Waves
11
I. I. The Nature of Magnetic WavesThe Nature of Magnetic Waves
1. What does a wave do?
• A wave transfers energy from one place to another without transferring matter.
• Yes. Mechanical waves and Electromagnetic waves
A. Waves In SpaceTransferring Energy
The Nature of Electromagnetic WavesThe Nature of Electromagnetic Waves
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2. Is there more than one type of wave?
1. What makes Mechanical waves different from Electromagnetic waves? • Mechanical waves are the types of waves
that use matter to transfer energy.
A. Waves In SpaceTransferring Energy
The Nature of Electromagnetic WavesThe Nature of Electromagnetic Waves
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• Waves, such as water waves and sound waves, are mechanical waves that transfer energy by making particles of matter move.
2. What makes Mechanical waves different from Electromagnetic waves? • Electromagnetic waves can travel through
empty space or through matter and is produced by charged particles that are in motion
A. Waves In SpaceTransferring Energy
The Nature of Electromagnetic WavesThe Nature of Electromagnetic Waves
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• Radio waves, microwaves, infrared waves, visible light, ultraviolet light, X-Rays, and Gamma Rays are all electromagnetic waves
1. What makes an electromagnetic wave?
2. What does a force field do?
B. Forces and Fields
The Nature of Electromagnetic WavesThe Nature of Electromagnetic Waves
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• An electromagnetic wave is made of two parts—an electric field and a magnetic field. These fields are force fields.
• A force field enables an object to exert forces on other objects, even though they are not touching.
3. What are some types of force fields?
B. Forces and Fields
The Nature of Electromagnetic WavesThe Nature of Electromagnetic Waves
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A. Earth is surrounded by a force field called the gravitational field
• A gravitational field surrounds all objects.
B. A magnetic field exerts a force on another magnet and on magnetic materials.
• Magnetic fields cause other magnets to line up along the direction of the magnetic field.
3. What are some types of force fields?
B. Forces and Fields
The Nature of Electromagnetic WavesThe Nature of Electromagnetic Waves
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C. A particle that has electric charge, such as a proton or an electron, is surrounded by an electric field. • The electric field is a force field that exerts
a force on all other charged particles that are in the field.
1. How are waves produced?
C. Making Electromagnetic Waves
The Nature of Electromagnetic WavesThe Nature of Electromagnetic Waves
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• A charged particle always is surrounded by an electric field.
• Electromagnetic waves are produced by charged particles, such as electrons, that move back and forth or vibrate.
• You can make a wave on a rope by shaking one end of the rope up and down.
C. Making Electromagnetic Waves
The Nature of Electromagnetic WavesThe Nature of Electromagnetic Waves
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In this figure electrons are flowing in a wire that carries an electric current. As a result, the wire is surrounded by a magnetic field.
1. How are waves produced?
C. Making Electromagnetic Waves
The Nature of Electromagnetic WavesThe Nature of Electromagnetic Waves
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• As a charged particle vibrates by moving up and down or back and forth, it produces changing electric and magnetic fields that move away from the vibrating charge in many directions
• These changing fields traveling in many directions form an electromagnetic wave.
D. Properties of Electromagnetic Waves
The Nature of Electromagnetic WavesThe Nature of Electromagnetic Waves
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1. What is the difference between Frequency and wavelength?
• The frequency of a wave is the number of wavelengths that pass by a point in 1 s.
• Wavelength is the distance from one crest to the next or from one trough to the next.
3. What is the name of the energy carried by an electromagnetic wave?
The Nature of Electromagnetic WavesThe Nature of Electromagnetic Waves
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2. What can be determined from frequency?
• The higher the frequency of the electromagnetic wave, the more energy it has.
D. Properties of Electromagnetic Waves
• The amount of energy that an electromagnetic wave carries.
• Radiant Energy.
4. What speed do all electromagnetic waves travel in space?
The Nature of Electromagnetic WavesThe Nature of Electromagnetic Waves
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• 300,000 km/s.
5. What is this speed sometimes called?
• The speed of light.
D. Properties of Electromagnetic Waves
11Section CheckSection Check
Question 1
A gravitational field surrounds _______.
all objects objects the size of Earth objects bigger than Earth objects bigger than the Sun
11Section CheckSection Check
Question 2
A _______ wave can’t travel through space from the Sun to the Earth, but an _______ wave can.
compressional, electromagnetic electromagnetic, mechanical mechanical, electromagnetic transverse, sound
11Section CheckSection Check
Question 3
What speed do all electromagnetic waves travel?
300,000 m/s 300,000 km/s 300,000 mi/hr 300,000 km/hr
The Nature of Electromagnetic WavesThe Nature of Electromagnetic Waves
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II. II. The Electromagnetic SpectrumThe Electromagnetic Spectrum
A. Electromagnetic Waves
1. How are electromagnetic waves classified?
The Electromagnetic SpectrumThe Electromagnetic Spectrum
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• The wide range of electromagnetic waves with different frequencies and wavelengths forms the electromagnetic spectrum.
The Electromagnetic SpectrumThe Electromagnetic Spectrum
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2. What are the different parts into which the electromagnetic spectrum is divided?
• Radio Waves • Microwaves • Infrared Waves • Visible Light • Ultraviolet light• X-Ray • Gamma Rays
A. Electromagnetic Waves
• Radio waves have wavelengths longer than about 0.3 m.
2a. Radio Waves
The Electromagnetic SpectrumThe Electromagnetic Spectrum
22A. Electromagnetic Waves
• Radio waves have the lowest frequencies of all the electromagnetic waves and carry the least energy.
The Electromagnetic SpectrumThe Electromagnetic Spectrum
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• As the electrons in the receiving antenna vibrate, they form an alternating current.
• Radio waves can cause electrons in another piece of metal, such as another antenna, to vibrate.
A. Electromagnetic Waves2a. Radio Waves
• Varying the frequency of the radio waves broadcast by the transmitting antenna changes the alternating current in the receiving antenna
• Microwaves have wavelengths between about 0.3 m and 0.001 m
• Microwaves have a higher frequency and a shorter wavelength than the waves that are used in your home radio.
The Electromagnetic SpectrumThe Electromagnetic Spectrum
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• Microwave ovens use microwaves to heat food.
2b. Microwaves
A. Electromagnetic Waves
The Electromagnetic SpectrumThe Electromagnetic Spectrum
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2b. Microwaves• Microwaves are used in Radar
• Radar, an acronym for RAdio Detecting And Ranging, uses electromagnetic waves to detect objects in the same way.
A. Electromagnetic Waves
• The heat you are sensing with your skin when you stand near a fire is from infrared waves.
The Electromagnetic SpectrumThe Electromagnetic Spectrum
22
• Infrared waves have wavelengths between about one thousandth and 0.7 millionths of a meter.
2c. Infrared Waves
A. Electromagnetic Waves
• Electromagnetic waves are emitted by every object.
The Electromagnetic SpectrumThe Electromagnetic Spectrum
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• Most of the electromagnetic waves given off by an object at room temperature are infrared waves and have a wavelength of about 0.000 01 m, or one hundred thousandth of a meter.
• Infrared detectors can detect objects that are warmer or cooler than their surroundings.
A. Electromagnetic Waves
2c. Infrared Waves• Detecting Infrared Waves
• Animals and Infrared Waves• Snakes called pit vipers have a pit located
between the nostril and the eye that detects infrared waves.
The Electromagnetic SpectrumThe Electromagnetic Spectrum
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• These pits help pit vipers hunt at night by detecting the infrared waves their prey emits.
A. Electromagnetic Waves
2c. Infrared Waves
• As the temperature of an object increases, the atoms and molecules in the object move faster.
The Electromagnetic SpectrumThe Electromagnetic Spectrum
22
• If the temperature is high enough, the object might glow.
• Electromagnetic waves you can detect with your eyes are called visible light.
A. Electromagnetic Waves
2c. Visible Light
• What you see as different colors are electromagnetic waves of different wavelengths.
The Electromagnetic SpectrumThe Electromagnetic Spectrum
22
• Red light has the longest wavelength (lowest frequency), and blue light has the shortest wavelength (highest frequency).
A. Electromagnetic Waves
2d. Visible Light
The Electromagnetic SpectrumThe Electromagnetic Spectrum
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• Ultraviolet radiation has higher frequencies than visible light and carries more energy.
• Ultraviolet radiation is higher in frequency than visible light and has even shorter wavelengths—between 0.4 millionths of a meter and about ten billionths of a meter.
A. Electromagnetic Waves
2e. Ultraviolet Radiation
• The Sun emits mainly infrared waves and visible light.
The Electromagnetic SpectrumThe Electromagnetic Spectrum
22
• Only about 8 percent of the electromagnetic waves emitted by the Sun are ultraviolet radiation.
A. Electromagnetic Waves
2e. Ultraviolet Radiation
• Beneficial Uses of UV Radiation• A few minutes of exposure each day to
ultraviolet radiation from the sun enables your body to produce the vitamin D it needs.
The Electromagnetic SpectrumThe Electromagnetic Spectrum
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• Because ultraviolet radiation can kill cells, it can be used to disinfect (kill bacteria) surface areas, water, and air.
A. Electromagnetic Waves
2e. Ultraviolet Radiation
The Electromagnetic SpectrumThe Electromagnetic Spectrum
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• X rays, with an even higher frequency than ultraviolet rays, have enough energy to go right through skin and muscle.
A. Electromagnetic Waves
2f. X-Ray
• The fact that X rays can pass through the human body makes them useful for medical diagnosis.
• X-ray images help doctors detect injuries and diseases, such as broken bones and cancer.
The Electromagnetic SpectrumThe Electromagnetic Spectrum
22
• Gamma rays are the hardest to stop. They are produced by changes in the nuclei of atoms.
• Gamma rays have the highest frequency and, therefore, carry the most energy.
A. Electromagnetic Waves
2g. Gamma Rays
• A beam of gamma rays focused on a cancerous tumor can kill the tumor.
• Gamma radiation also can kill disease-causing bacteria in food.
Radio Frequency Electromagnetic spectrum Light Spectrum Wave Frequencies
22Section CheckSection Check
Question 1
Electromagnetic energy comes in a variety of wavelengths and frequencies. The whole range is collectively known as the _______.
22Section CheckSection Check
Question 2Electromagnetic waves with a wavelength longer than 0.3 meters have a familiar name. What are they called?
Radio Waves X-Rays Light Waves Tidal Waves
22Section CheckSection Check
Question 3Electromagnetic radiation of a lower frequency than visible light is known as _______.
beta radiation gamma radiation infrared radiation X rays
A. Telecommunications• Today you can talk to
someone far away or transmit and receive information over long distances almost instantly.
• Thanks to telecommunications, the world is becoming increasingly connected through the use of electromagnetic waves.
Using Electromagnetic WavesUsing Electromagnetic Waves
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B. Using Radio Waves
• Using radio waves to communicate has several advantages.
• For example, radio waves pass through walls and windows easily.
Using Electromagnetic WavesUsing Electromagnetic Waves
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• Radio waves do not interact with humans, so they are not harmful to people like ultraviolet rays or X rays are.
B. Using Radio Waves
Using Electromagnetic WavesUsing Electromagnetic Waves
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• This figure shows how radio waves can be used to transmit information—in this casetransmitting information that enables sounds to be reproduced at a location far away.
1. Radio Transmission
Using Electromagnetic WavesUsing Electromagnetic Waves
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• To carry information on the carrier wave, either the amplitude or the frequency of the carrier wave is changed, or modulated.
• The radio waves broadcast by a station at its assigned frequency are the carrier waves for that station.
B. Using Radio Waves
• The letters AM in AM radio stand for amplitude modulation, which means that the amplitude of the carrier wave is changed to transmit information.
Using Electromagnetic WavesUsing Electromagnetic Waves
33B. Using Radio Waves
2. Amplitude Modulation
Using Electromagnetic WavesUsing Electromagnetic Waves
33B. Using Radio Waves
2. Amplitude Modulation• The original sound is transformed into an
electrical signal that is used to vary the amplitude of the carrier wave.
Using Electromagnetic WavesUsing Electromagnetic Waves
33B. Using Radio Waves
3. Frequency Modulation• FM radio works in much the same way as
AM radio, but the frequency instead of the amplitude is modulated
Using Electromagnetic WavesUsing Electromagnetic Waves
33B. Using Radio Waves
3. Frequency Modulation• An FM receiver contains electronic
components that use the varying frequency of the carrier wave to produce an electrical signal.
C. Telephones1. What is a telephone and how does it work?
Using Electromagnetic WavesUsing Electromagnetic Waves
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• The electric signal is carried through a wire to the telephone switching systems.
• There, the signal might be sent through other wires or be converted into a radio or microwave signal for transmission through the air.
• A telephone contains a microphone in the mouthpiece that converts a sound wave into an electric signal.
C. Telephones
• At the receiving end, the signal is converted back to an electric signal.
Using Electromagnetic WavesUsing Electromagnetic Waves
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• A speaker in the earpiece of the phone changes the electric signal into a sound wave.
1. What is a telephone and how does it work?
2. Remote Phones
Using Electromagnetic WavesUsing Electromagnetic Waves
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• In a cordless phone, the electrical signal produced by the microphone is transmitted through an antenna in the phone to the base station.
C. Telephones
• A cellular phone communicates with a base station that can be many kilometers away.
Using Electromagnetic WavesUsing Electromagnetic Waves
33
• The base station uses a large antenna to communicate with the cell phone and with other base stations in the cell phone network.
2. Remote PhonesC. Telephones
• When you dial a pager, the signal is sent to a base station.
Using Electromagnetic WavesUsing Electromagnetic Waves
33
• From there, an electromagnetic signal is sent to the pager.
• The pager beeps or vibrates to indicate that someone has called.
C. Telephones
3. Pagers
D. Communications Satellites
1. How are radio signals sent around the world? .
Using Electromagnetic WavesUsing Electromagnetic Waves
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• Radio signals are sent to satellites.
• The satellites can communicate with other satellites or with ground stations.
E. The Global Positioning System
• Global Positioning System, or GPS. GPS is used to locate objects on Earth.
Using Electromagnetic WavesUsing Electromagnetic Waves
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• The system consists of satellites, ground-based stations, and portable units with receivers.
1. What is GPS?
E. The Global Positioning System
• A GPS receiver measures the time it takes for radio waves to travel from several satellites to the receiver. This determines the distance to each satellite
Using Electromagnetic WavesUsing Electromagnetic Waves
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• The receiver uses the distances to calculate its latitude, longitude, and elevation.
2. How does a GPS locate an object?
Section CheckSection Check
33
Name some of the reasons radio waves are useful to us.
Question 1
They travel long distances, pass through walls easily, don’t harm people, and are ideal for communications purposes.
Answer
Section CheckSection Check
33
As you turn the dial on a radio, you pick up different frequencies. Each station is assigned its own frequency known as that station’s _______.
Question 2
The answer is carrier wave. This is designed to prevent stations from overlapping each other’s signals.
Answer
Section CheckSection Check
33
What does AM stand for when referring to radio signals?
Question 3
It stands for amplitude modulation. FM stands for frequency modulation.
Answer
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