Radio 1

RadioRadio

Radio 2

Observations about Observations about RadioRadio

Transmit sound long distances without Transmit sound long distances without wireswires

Involve antennasInvolve antennas Seem to involve electricity and Seem to involve electricity and

magnetismmagnetism Reception depends on antenna Reception depends on antenna

positioningpositioning Reception weakens with distanceReception weakens with distance Two styles of radio: AM and FMTwo styles of radio: AM and FM

Radio 3

3 Questions about Radio3 Questions about Radio

How can a radio wave exist?How can a radio wave exist? How is a radio wave emitted and How is a radio wave emitted and

received?received? How can a radio wave represent How can a radio wave represent

sound?sound?

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Question 1Question 1

How can a radio wave exist?How can a radio wave exist? What is an electromagnetic wave What is an electromagnetic wave

anyway?anyway? How can an electric field exist without How can an electric field exist without

charge?charge? How can a magnetic field exist without How can a magnetic field exist without

pole?pole?

Radio 5

Electromagnetic WavesElectromagnetic Waves

Radio waves are a type of Radio waves are a type of electromagnetic waveelectromagnetic wave a structure in space consisting only of an a structure in space consisting only of an

electric field and a magnetic fieldelectric field and a magnetic field Electromagnetic waves areElectromagnetic waves are

emitted or received by charge or poleemitted or received by charge or pole but are self-sustaining while traveling in but are self-sustaining while traveling in

vacuum.vacuum. Their electric and magnetic fields create Their electric and magnetic fields create

one anotherone another

Radio 6

Electromagnetism Electromagnetism (Version (Version 3)3)

Magnetic fields are produced byMagnetic fields are produced by magnetic poles (but free poles don’t magnetic poles (but free poles don’t

seem to exist),seem to exist), moving electric charges,moving electric charges, and changing electric fieldsand changing electric fields..

Electric fields are produced byElectric fields are produced by electric charges,electric charges, moving magnetic poles,moving magnetic poles, and changing magnetic fields.and changing magnetic fields.

Radio 7

Structure of a Radio Structure of a Radio WaveWave

Electric field is perpendicular to Electric field is perpendicular to magnetic fieldmagnetic field

Changing electric fieldChanging electric fieldcreates magnetic fieldcreates magnetic field

Changing magnetic fieldChanging magnetic fieldcreates electric fieldcreates electric field

Polarization of the wavePolarization of the waveis associated with theis associated with thewave’s electric fieldwave’s electric field

Radio 8

Question 2Question 2

How is a radio wave emitted and How is a radio wave emitted and received?received?

Radio 9

Launching a Radio WaveLaunching a Radio Wave

Accelerating charge emits Accelerating charge emits electromagnetic waveselectromagnetic waves

The more charge and the harder it The more charge and the harder it accelerates, the stronger the resulting accelerates, the stronger the resulting electromagnetic waveelectromagnetic wave

Radio stations need to emit strong wavesRadio stations need to emit strong waves so they move large amounts of chargeso they move large amounts of charge with the help of resonant devices: tank with the help of resonant devices: tank

circuitscircuits

Radio 10

A Tank CircuitA Tank Circuit

is a harmonic oscillator for charge and is a harmonic oscillator for charge and currentcurrent

Charge flows regularly back and forth Charge flows regularly back and forth fromfromone capacitor plate to the other, through one capacitor plate to the other, through the inductor.the inductor.

Its total energy shiftsIts total energy shiftsback and forth betweenback and forth betweenits inductor andits inductor andits capacitor.its capacitor.

Radio 11

Tank Circuit OscillationTank Circuit Oscillation

The frequency of the tankThe frequency of the tankcircuit is determined only by itscircuit is determined only by itsinductance and its capacitance.inductance and its capacitance.

It can store a great deal of energyIt can store a great deal of energyand have an enormous amountand have an enormous amountof charge moving through it.of charge moving through it.

Tank circuits come in manyTank circuits come in manyshapes, including straight lines!shapes, including straight lines!

Radio 12

Tank Circuits in RadioTank Circuits in Radio

Tanks build up energy at a specific Tanks build up energy at a specific frequencyfrequency

Two tanks help radios Two tanks help radios emitemit radio radio waveswaves The first tank circuit feeds the antennaThe first tank circuit feeds the antenna The second tank circuit is the antennaThe second tank circuit is the antenna

Two similar tanks help radios Two similar tanks help radios detectdetect radio wavesradio waves

Radio 13

Emitting Radio Waves Emitting Radio Waves (Part 1)(Part 1)

A transmitter uses a tank circuit to A transmitter uses a tank circuit to “slosh” charge up and down its “slosh” charge up and down its antenna,antenna,which acts as a second tank.which acts as a second tank.

A receiver uses a tank circuit toA receiver uses a tank circuit todetect charge “sloshing” on itsdetect charge “sloshing” on itstank-circuit antenna.tank-circuit antenna.

Transmitter antenna chargeTransmitter antenna chargeaffects receiver antenna chargeaffects receiver antenna charge

Antenna orientations matter!Antenna orientations matter!

Radio 14

Emitting Radio Waves Emitting Radio Waves (Part 2)(Part 2)

Accelerating charge emits radio wavesAccelerating charge emits radio waves Charge produces electric fieldCharge produces electric field Current produces magnetic fieldCurrent produces magnetic field Changing current produces changing Changing current produces changing

magnetic field, produces changing magnetic field, produces changing electric field, prod…electric field, prod…

A radio wave consists only of an A radio wave consists only of an electric and magnetic fieldelectric and magnetic field

A radio wave travels through empty A radio wave travels through empty space at the speed of lightspace at the speed of light

Radio 15

Question 3Question 3

How can a radio wave represent How can a radio wave represent sound?sound?

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AM ModulationAM Modulation

Information can be encoded as a Information can be encoded as a fluctuating fluctuating amplitudeamplitude of the radio of the radio wavewave

The air pressure variationsThe air pressure variationsthat are sound causethat are sound causechanges in the amount ofchanges in the amount ofcharge moving on thecharge moving on theantennaantenna

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FM ModulationFM Modulation

Information can be encoded as a Information can be encoded as a fluctuating fluctuating frequencyfrequency of the radio of the radio wavewave

The air pressure variationsThe air pressure variationsthat are sound causethat are sound causeslight shifts in theslight shifts in thefrequency of chargefrequency of chargemotion on the antennamotion on the antenna

Radio 18

Summary about RadioSummary about Radio

Radio waves are emitted by charge Radio waves are emitted by charge accelerating on a transmitting antennaaccelerating on a transmitting antenna

Radio waves are detected when they Radio waves are detected when they cause charge to accelerate on a receiving cause charge to accelerate on a receiving antennaantenna

Radio waves consist only of self-sustaining Radio waves consist only of self-sustaining electric and magnetic fieldselectric and magnetic fields

Radio waves can represent sound Radio waves can represent sound information as variations in amplitude or information as variations in amplitude or frequencyfrequency