The Nature of Electromagnetic Waves 1 1 I. The Nature of Magnetic Waves.

The Nature of Electromagnetic WavesThe Nature of Electromagnetic Waves

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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


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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.



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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



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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


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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?



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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?



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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


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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.



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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?



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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


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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?


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2. What can be determined from frequency?

• The higher the frequency of the electromagnetic wave, the more energy it has.


• The amount of energy that an electromagnetic wave carries.

• Radiant Energy.

4. What speed do all electromagnetic waves travel in space?


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• 300,000 km/s.

5. What is this speed sometimes called?

• The speed of light.


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


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


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


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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.


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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


• Radio waves have wavelengths longer than about 0.3 m.

2a. Radio Waves


22A. Electromagnetic Waves

• Radio waves have the lowest frequencies of all the electromagnetic waves and carry the least energy.


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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.


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• Microwave ovens use microwaves to heat food.

2b. Microwaves



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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.


• The heat you are sensing with your skin when you stand near a fire is from infrared waves.


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• Infrared waves have wavelengths between about one thousandth and 0.7 millionths of a meter.

2c. Infrared Waves


• Electromagnetic waves are emitted by every object.


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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.


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.


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• These pits help pit vipers hunt at night by detecting the infrared waves their prey emits.


2c. Infrared Waves

• As the temperature of an object increases, the atoms and molecules in the object move faster.


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• If the temperature is high enough, the object might glow.

• Electromagnetic waves you can detect with your eyes are called visible light.


2c. Visible Light

• What you see as different colors are electromagnetic waves of different wavelengths.


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• Red light has the longest wavelength (lowest frequency), and blue light has the shortest wavelength (highest frequency).


2d. Visible Light


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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.


2e. Ultraviolet Radiation

• The Sun emits mainly infrared waves and visible light.


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• Only about 8 percent of the electromagnetic waves emitted by the Sun are 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.


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• Because ultraviolet radiation can kill cells, it can be used to disinfect (kill bacteria) surface areas, water, and air.




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• X rays, with an even higher frequency than ultraviolet rays, have enough energy to go right through skin and muscle.


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.


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• 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.


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


Question 1

Electromagnetic energy comes in a variety of wavelengths and frequencies. The whole range is collectively known as the _______.


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


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.


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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.



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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


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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.


• The letters AM in AM radio stand for amplitude modulation, which means that the amplitude of the carrier wave is changed to transmit information.


33B. Using Radio Waves

2. Amplitude Modulation



2. Amplitude Modulation• The original sound is transformed into an

electrical signal that is used to vary the amplitude of the carrier wave.



3. Frequency Modulation• FM radio works in much the same way as

AM radio, but the frequency instead of the amplitude is modulated



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?


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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.


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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


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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.


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• 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.


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• 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? .


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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.


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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


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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

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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


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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


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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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The Nature of Electromagnetic Waves 1 1 I. The Nature of Magnetic Waves.

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