UCSD Physics 10

Spring 2008 1

ElectromagnetismElectromagnetism

bull Electricity and magnetism are different facets of Electricity and magnetism are different facets of electromagnetismelectromagnetismndash a moving electric charge produces magnetic fields

ndash changing magnetic fields move electric charges

bull This connection first elucidated by Faraday MaxwellThis connection first elucidated by Faraday Maxwellbull Einstein saw electricity and magnetism as frame-Einstein saw electricity and magnetism as frame-

dependent facets of dependent facets of unifiedunified electromagneticelectromagnetic force force

UCSD Physics 10

Spring 2008 2

Magnetic fields from electricityMagnetic fields from electricitybull A static distribution of charges produces an electric A static distribution of charges produces an electric

fieldfieldbull Charges in Charges in motionmotion (an electrical current) produce a (an electrical current) produce a

magnetic fieldmagnetic fieldndash electric current is an example of charges (electrons) in motion

UCSD Physics 10

Spring 2008 3

ElectromagnetsElectromagnetsbull Arranging wire in a coil and running a current Arranging wire in a coil and running a current

through produces a magnetic field that looks a lot through produces a magnetic field that looks a lot like a bar magnetlike a bar magnetndash called an electromagnet

ndash putting a real magnet inside can shove the magnet back and forth depending on current direction called a solenoid

UCSD Physics 10

Spring 2008 4

Induced CurrentInduced Currentbull The next part of the story is that a The next part of the story is that a changingchanging

magnetic fieldmagnetic field produces an electric current in a produces an electric current in a loop surrounding the fieldloop surrounding the fieldndash called electromagnetic induction or Faradayrsquos Law

UCSD Physics 10

Spring 2008 5

The Electromagnetic ConnectionThe Electromagnetic Connection

bull A A changingchanging magnetic field produces an electric field and a magnetic field produces an electric field and a changing electric field produces a magnetic field changing electric field produces a magnetic field

bull Electric and Magnetic fields can produce forces on chargesElectric and Magnetic fields can produce forces on charges

bull An An acceleratingaccelerating charge produces electromagnetic waves charge produces electromagnetic waves (radiation)(radiation)

bull Both electric and magnetic fields can transport energyBoth electric and magnetic fields can transport energyndash Electric field energy used in electrical circuits eg released in

lightning

ndash Magnetic field carries energy through transformer for example

UCSD Physics 10

Spring 2008 6

Electromagnetic RadiationElectromagnetic Radiation

bull Interrelated electric and magnetic fields traveling through spaceInterrelated electric and magnetic fields traveling through space

bull All electromagnetic radiation travels at All electromagnetic radiation travels at cc = 3 = 3101088 ms ms in in vacuum ndash vacuum ndash thethe cosmic speed limit cosmic speed limitndash real number is 2997924580 ms exactly

UCSD Physics 10

Spring 2008 7

Whatrsquos ldquoWavingrdquo in EM wavesWhatrsquos ldquoWavingrdquo in EM wavesbull What medium transports sound wavesWhat medium transports sound waves

ndash Can there be sound waves in the vacuum of outer space

bull What medium transports water wavesWhat medium transports water waves

bull What medium transports radio wavesWhat medium transports radio waves

bull A topic of considerable debate in the late 1800rsquos and early A topic of considerable debate in the late 1800rsquos and early 1900rsquos1900rsquos

bull Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible ldquojellordquo that was thought to vibrate electromagnetically ldquojellordquo that was thought to vibrate electromagnetically

bull Experiments that sought this ether didnrsquot find it Experiments that sought this ether didnrsquot find it

bull This was quite a surpriseThis was quite a surprise

Electromagnetic waves travel through empty space

UCSD Physics 10

Spring 2008 8

Whatrsquos ldquoWavingrdquo in EM wavesWhatrsquos ldquoWavingrdquo in EM wavesbull What medium transports sound waves What medium transports sound waves AirAir

ndash Can there be sound waves in the vacuum of outer space No

bull What medium transports water waves What medium transports water waves Water (fluids)Water (fluids)

bull What medium transports radio waves What medium transports radio waves AirAir

bull A topic of considerable debate in the late 1800rsquos and early A topic of considerable debate in the late 1800rsquos and early 1900rsquos1900rsquos

bull Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible ldquojellordquo that was thought to vibrate electromagnetically ldquojellordquo that was thought to vibrate electromagnetically

bull Experiments that sought this ether didnrsquot find it Experiments that sought this ether didnrsquot find it

bull This was quite a surpriseThis was quite a surprise

Electromagnetic waves travel through empty spaceNo medium required

UCSD Physics 10

Spring 2008 9

Examples of Electromagnetic RadiationExamples of Electromagnetic Radiation

bull AM and FM radio waves (including TV signals)AM and FM radio waves (including TV signals)ndash Cell phone communication links

bull MicrowavesMicrowavesbull Infrared radiationInfrared radiationbull Light Light bull Ultra-violet raysUltra-violet raysbull X-raysX-raysbull Gamma raysGamma raysbull Frequency distinguishes these from one anotherFrequency distinguishes these from one another

UCSD Physics 10

Spring 2008 10

Uses of Electromagnetic WavesUses of Electromagnetic Wavesbull Communication systems (radio)Communication systems (radio)

ndash One-way and two-way

ndash Radar

bull Cooking (microwaves)Cooking (microwaves)

bull ldquoldquoNight Visionrdquo or heat (infrared)Night Visionrdquo or heat (infrared)

bull Sun tanning (Ultra-violet)Sun tanning (Ultra-violet)

bull Medical Imaging (X rays)Medical Imaging (X rays)

bull Astronomy (radio Astronomy (radio wave IR visible light UV gamma)wave IR visible light UV gamma)

All that we experience through our eyes is conveyed byelectromagnetic radiationhellip

UCSD Physics 10

Spring 2008 11

The Electromagnetic SpectrumThe Electromagnetic Spectrum

bull Relationship between frequency speed and Relationship between frequency speed and wavelengthwavelength

f f = c = c ff is frequency is frequency is wavelength is wavelength cc is speed of light is speed of lightbull Different frequencies of electromagnetic radiation Different frequencies of electromagnetic radiation

are better suited to different purposesare better suited to different purposesbull The frequency of a radio wave determines its The frequency of a radio wave determines its

propagation characteristics through various mediapropagation characteristics through various media

UCSD Physics 10

Spring 2008 12

US Frequency Allocation ndash the FCCUS Frequency Allocation ndash the FCC

(300 MHz has a wavelength of 1 meter)

ldquoRadiordquo frequency-space is allocated to the hiltHerersquos a sample region from 300ndash600 MHz

International allocation gets tricky

UCSD Physics 10

Spring 2008 13

Generation of Radio WavesGeneration of Radio Waves

bull Accelerating charges radiate EM energyAccelerating charges radiate EM energybull If charges oscillate back and forth get time-varying fieldsIf charges oscillate back and forth get time-varying fields

E

+++

+

UCSD Physics 10

Spring 2008 14

Generation of Radio WavesGeneration of Radio Waves

If charges oscillate back and forth get time-varying magnetic fields tooIf charges oscillate back and forth get time-varying magnetic fields tooNote that the magnetic fields are perpendicular to the electric field vectorsNote that the magnetic fields are perpendicular to the electric field vectors

B

+++

+

UCSD Physics 10

Spring 2008 15

Polarization of Radio WavesPolarization of Radio Waves

B

ETransmitting antenna

UCSD Physics 10

Spring 2008 16

Reception of Radio WavesReception of Radio Waves

Receiving antenna works best when lsquotunedrsquo to the

wavelength of the signal and has proper polarization

Electrons in antenna are ldquojiggledrdquoby passage of electromagnetic wave

B

E

Optimal antenna length is one quarter-wavelength (4)

UCSD Physics 10

Spring 2008 2

Magnetic fields from electricityMagnetic fields from electricitybull A static distribution of charges produces an electric A static distribution of charges produces an electric

fieldfieldbull Charges in Charges in motionmotion (an electrical current) produce a (an electrical current) produce a

magnetic fieldmagnetic fieldndash electric current is an example of charges (electrons) in motion

UCSD Physics 10

Spring 2008 3

ElectromagnetsElectromagnetsbull Arranging wire in a coil and running a current Arranging wire in a coil and running a current

through produces a magnetic field that looks a lot through produces a magnetic field that looks a lot like a bar magnetlike a bar magnetndash called an electromagnet

ndash putting a real magnet inside can shove the magnet back and forth depending on current direction called a solenoid

UCSD Physics 10

Spring 2008 4

Induced CurrentInduced Currentbull The next part of the story is that a The next part of the story is that a changingchanging

magnetic fieldmagnetic field produces an electric current in a produces an electric current in a loop surrounding the fieldloop surrounding the fieldndash called electromagnetic induction or Faradayrsquos Law

UCSD Physics 10

Spring 2008 5

The Electromagnetic ConnectionThe Electromagnetic Connection

bull A A changingchanging magnetic field produces an electric field and a magnetic field produces an electric field and a changing electric field produces a magnetic field changing electric field produces a magnetic field

bull Electric and Magnetic fields can produce forces on chargesElectric and Magnetic fields can produce forces on charges

bull An An acceleratingaccelerating charge produces electromagnetic waves charge produces electromagnetic waves (radiation)(radiation)

bull Both electric and magnetic fields can transport energyBoth electric and magnetic fields can transport energyndash Electric field energy used in electrical circuits eg released in

lightning

ndash Magnetic field carries energy through transformer for example

UCSD Physics 10

Spring 2008 6

Electromagnetic RadiationElectromagnetic Radiation

bull Interrelated electric and magnetic fields traveling through spaceInterrelated electric and magnetic fields traveling through space

bull All electromagnetic radiation travels at All electromagnetic radiation travels at cc = 3 = 3101088 ms ms in in vacuum ndash vacuum ndash thethe cosmic speed limit cosmic speed limitndash real number is 2997924580 ms exactly

UCSD Physics 10

Spring 2008 7

Whatrsquos ldquoWavingrdquo in EM wavesWhatrsquos ldquoWavingrdquo in EM wavesbull What medium transports sound wavesWhat medium transports sound waves

ndash Can there be sound waves in the vacuum of outer space

bull What medium transports water wavesWhat medium transports water waves

bull What medium transports radio wavesWhat medium transports radio waves

bull A topic of considerable debate in the late 1800rsquos and early A topic of considerable debate in the late 1800rsquos and early 1900rsquos1900rsquos

bull Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible ldquojellordquo that was thought to vibrate electromagnetically ldquojellordquo that was thought to vibrate electromagnetically

bull Experiments that sought this ether didnrsquot find it Experiments that sought this ether didnrsquot find it

bull This was quite a surpriseThis was quite a surprise

Electromagnetic waves travel through empty space

UCSD Physics 10

Spring 2008 8

Whatrsquos ldquoWavingrdquo in EM wavesWhatrsquos ldquoWavingrdquo in EM wavesbull What medium transports sound waves What medium transports sound waves AirAir

ndash Can there be sound waves in the vacuum of outer space No

bull What medium transports water waves What medium transports water waves Water (fluids)Water (fluids)

bull What medium transports radio waves What medium transports radio waves AirAir

bull A topic of considerable debate in the late 1800rsquos and early A topic of considerable debate in the late 1800rsquos and early 1900rsquos1900rsquos

bull Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible ldquojellordquo that was thought to vibrate electromagnetically ldquojellordquo that was thought to vibrate electromagnetically

bull Experiments that sought this ether didnrsquot find it Experiments that sought this ether didnrsquot find it

bull This was quite a surpriseThis was quite a surprise

Electromagnetic waves travel through empty spaceNo medium required

UCSD Physics 10

Spring 2008 9

Examples of Electromagnetic RadiationExamples of Electromagnetic Radiation

bull AM and FM radio waves (including TV signals)AM and FM radio waves (including TV signals)ndash Cell phone communication links

bull MicrowavesMicrowavesbull Infrared radiationInfrared radiationbull Light Light bull Ultra-violet raysUltra-violet raysbull X-raysX-raysbull Gamma raysGamma raysbull Frequency distinguishes these from one anotherFrequency distinguishes these from one another

UCSD Physics 10

Spring 2008 10

Uses of Electromagnetic WavesUses of Electromagnetic Wavesbull Communication systems (radio)Communication systems (radio)

ndash One-way and two-way

ndash Radar

bull Cooking (microwaves)Cooking (microwaves)

bull ldquoldquoNight Visionrdquo or heat (infrared)Night Visionrdquo or heat (infrared)

bull Sun tanning (Ultra-violet)Sun tanning (Ultra-violet)

bull Medical Imaging (X rays)Medical Imaging (X rays)

bull Astronomy (radio Astronomy (radio wave IR visible light UV gamma)wave IR visible light UV gamma)

All that we experience through our eyes is conveyed byelectromagnetic radiationhellip

UCSD Physics 10

Spring 2008 11

The Electromagnetic SpectrumThe Electromagnetic Spectrum

bull Relationship between frequency speed and Relationship between frequency speed and wavelengthwavelength

f f = c = c ff is frequency is frequency is wavelength is wavelength cc is speed of light is speed of lightbull Different frequencies of electromagnetic radiation Different frequencies of electromagnetic radiation

are better suited to different purposesare better suited to different purposesbull The frequency of a radio wave determines its The frequency of a radio wave determines its

propagation characteristics through various mediapropagation characteristics through various media

UCSD Physics 10

Spring 2008 12

US Frequency Allocation ndash the FCCUS Frequency Allocation ndash the FCC

(300 MHz has a wavelength of 1 meter)

ldquoRadiordquo frequency-space is allocated to the hiltHerersquos a sample region from 300ndash600 MHz

International allocation gets tricky

UCSD Physics 10

Spring 2008 13

Generation of Radio WavesGeneration of Radio Waves

bull Accelerating charges radiate EM energyAccelerating charges radiate EM energybull If charges oscillate back and forth get time-varying fieldsIf charges oscillate back and forth get time-varying fields

E

+++

+

UCSD Physics 10

Spring 2008 14

Generation of Radio WavesGeneration of Radio Waves

If charges oscillate back and forth get time-varying magnetic fields tooIf charges oscillate back and forth get time-varying magnetic fields tooNote that the magnetic fields are perpendicular to the electric field vectorsNote that the magnetic fields are perpendicular to the electric field vectors

B

+++

+

UCSD Physics 10

Spring 2008 15

Polarization of Radio WavesPolarization of Radio Waves

B

ETransmitting antenna

UCSD Physics 10

Spring 2008 16

Reception of Radio WavesReception of Radio Waves

Receiving antenna works best when lsquotunedrsquo to the

wavelength of the signal and has proper polarization

Electrons in antenna are ldquojiggledrdquoby passage of electromagnetic wave

B

E

Optimal antenna length is one quarter-wavelength (4)

UCSD Physics 10

Spring 2008 3

ElectromagnetsElectromagnetsbull Arranging wire in a coil and running a current Arranging wire in a coil and running a current

through produces a magnetic field that looks a lot through produces a magnetic field that looks a lot like a bar magnetlike a bar magnetndash called an electromagnet

ndash putting a real magnet inside can shove the magnet back and forth depending on current direction called a solenoid

UCSD Physics 10

Spring 2008 4

Induced CurrentInduced Currentbull The next part of the story is that a The next part of the story is that a changingchanging

magnetic fieldmagnetic field produces an electric current in a produces an electric current in a loop surrounding the fieldloop surrounding the fieldndash called electromagnetic induction or Faradayrsquos Law

UCSD Physics 10

Spring 2008 5

The Electromagnetic ConnectionThe Electromagnetic Connection

bull A A changingchanging magnetic field produces an electric field and a magnetic field produces an electric field and a changing electric field produces a magnetic field changing electric field produces a magnetic field

bull Electric and Magnetic fields can produce forces on chargesElectric and Magnetic fields can produce forces on charges

bull An An acceleratingaccelerating charge produces electromagnetic waves charge produces electromagnetic waves (radiation)(radiation)

bull Both electric and magnetic fields can transport energyBoth electric and magnetic fields can transport energyndash Electric field energy used in electrical circuits eg released in

lightning

ndash Magnetic field carries energy through transformer for example

UCSD Physics 10

Spring 2008 6

Electromagnetic RadiationElectromagnetic Radiation

bull Interrelated electric and magnetic fields traveling through spaceInterrelated electric and magnetic fields traveling through space

bull All electromagnetic radiation travels at All electromagnetic radiation travels at cc = 3 = 3101088 ms ms in in vacuum ndash vacuum ndash thethe cosmic speed limit cosmic speed limitndash real number is 2997924580 ms exactly

UCSD Physics 10

Spring 2008 7

Whatrsquos ldquoWavingrdquo in EM wavesWhatrsquos ldquoWavingrdquo in EM wavesbull What medium transports sound wavesWhat medium transports sound waves

ndash Can there be sound waves in the vacuum of outer space

bull What medium transports water wavesWhat medium transports water waves

bull What medium transports radio wavesWhat medium transports radio waves

bull A topic of considerable debate in the late 1800rsquos and early A topic of considerable debate in the late 1800rsquos and early 1900rsquos1900rsquos

bull Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible ldquojellordquo that was thought to vibrate electromagnetically ldquojellordquo that was thought to vibrate electromagnetically

bull Experiments that sought this ether didnrsquot find it Experiments that sought this ether didnrsquot find it

bull This was quite a surpriseThis was quite a surprise

Electromagnetic waves travel through empty space

UCSD Physics 10

Spring 2008 8

Whatrsquos ldquoWavingrdquo in EM wavesWhatrsquos ldquoWavingrdquo in EM wavesbull What medium transports sound waves What medium transports sound waves AirAir

ndash Can there be sound waves in the vacuum of outer space No

bull What medium transports water waves What medium transports water waves Water (fluids)Water (fluids)

bull What medium transports radio waves What medium transports radio waves AirAir

bull A topic of considerable debate in the late 1800rsquos and early A topic of considerable debate in the late 1800rsquos and early 1900rsquos1900rsquos

bull Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible ldquojellordquo that was thought to vibrate electromagnetically ldquojellordquo that was thought to vibrate electromagnetically

bull Experiments that sought this ether didnrsquot find it Experiments that sought this ether didnrsquot find it

bull This was quite a surpriseThis was quite a surprise

Electromagnetic waves travel through empty spaceNo medium required

UCSD Physics 10

Spring 2008 9

Examples of Electromagnetic RadiationExamples of Electromagnetic Radiation

bull AM and FM radio waves (including TV signals)AM and FM radio waves (including TV signals)ndash Cell phone communication links

bull MicrowavesMicrowavesbull Infrared radiationInfrared radiationbull Light Light bull Ultra-violet raysUltra-violet raysbull X-raysX-raysbull Gamma raysGamma raysbull Frequency distinguishes these from one anotherFrequency distinguishes these from one another

UCSD Physics 10

Spring 2008 10

Uses of Electromagnetic WavesUses of Electromagnetic Wavesbull Communication systems (radio)Communication systems (radio)

ndash One-way and two-way

ndash Radar

bull Cooking (microwaves)Cooking (microwaves)

bull ldquoldquoNight Visionrdquo or heat (infrared)Night Visionrdquo or heat (infrared)

bull Sun tanning (Ultra-violet)Sun tanning (Ultra-violet)

bull Medical Imaging (X rays)Medical Imaging (X rays)

bull Astronomy (radio Astronomy (radio wave IR visible light UV gamma)wave IR visible light UV gamma)

All that we experience through our eyes is conveyed byelectromagnetic radiationhellip

UCSD Physics 10

Spring 2008 11

The Electromagnetic SpectrumThe Electromagnetic Spectrum

bull Relationship between frequency speed and Relationship between frequency speed and wavelengthwavelength

f f = c = c ff is frequency is frequency is wavelength is wavelength cc is speed of light is speed of lightbull Different frequencies of electromagnetic radiation Different frequencies of electromagnetic radiation

are better suited to different purposesare better suited to different purposesbull The frequency of a radio wave determines its The frequency of a radio wave determines its

propagation characteristics through various mediapropagation characteristics through various media

UCSD Physics 10

Spring 2008 12

US Frequency Allocation ndash the FCCUS Frequency Allocation ndash the FCC

(300 MHz has a wavelength of 1 meter)

ldquoRadiordquo frequency-space is allocated to the hiltHerersquos a sample region from 300ndash600 MHz

International allocation gets tricky

UCSD Physics 10

Spring 2008 13

Generation of Radio WavesGeneration of Radio Waves

bull Accelerating charges radiate EM energyAccelerating charges radiate EM energybull If charges oscillate back and forth get time-varying fieldsIf charges oscillate back and forth get time-varying fields

E

+++

+

UCSD Physics 10

Spring 2008 14

Generation of Radio WavesGeneration of Radio Waves

If charges oscillate back and forth get time-varying magnetic fields tooIf charges oscillate back and forth get time-varying magnetic fields tooNote that the magnetic fields are perpendicular to the electric field vectorsNote that the magnetic fields are perpendicular to the electric field vectors

B

+++

+

UCSD Physics 10

Spring 2008 15

Polarization of Radio WavesPolarization of Radio Waves

B

ETransmitting antenna

UCSD Physics 10

Spring 2008 16

Reception of Radio WavesReception of Radio Waves

Receiving antenna works best when lsquotunedrsquo to the

wavelength of the signal and has proper polarization

Electrons in antenna are ldquojiggledrdquoby passage of electromagnetic wave

B

E

Optimal antenna length is one quarter-wavelength (4)

UCSD Physics 10

Spring 2008 4

Induced CurrentInduced Currentbull The next part of the story is that a The next part of the story is that a changingchanging

magnetic fieldmagnetic field produces an electric current in a produces an electric current in a loop surrounding the fieldloop surrounding the fieldndash called electromagnetic induction or Faradayrsquos Law

UCSD Physics 10

Spring 2008 5

The Electromagnetic ConnectionThe Electromagnetic Connection

bull A A changingchanging magnetic field produces an electric field and a magnetic field produces an electric field and a changing electric field produces a magnetic field changing electric field produces a magnetic field

bull Electric and Magnetic fields can produce forces on chargesElectric and Magnetic fields can produce forces on charges

bull An An acceleratingaccelerating charge produces electromagnetic waves charge produces electromagnetic waves (radiation)(radiation)

bull Both electric and magnetic fields can transport energyBoth electric and magnetic fields can transport energyndash Electric field energy used in electrical circuits eg released in

lightning

ndash Magnetic field carries energy through transformer for example

UCSD Physics 10

Spring 2008 6

Electromagnetic RadiationElectromagnetic Radiation

bull Interrelated electric and magnetic fields traveling through spaceInterrelated electric and magnetic fields traveling through space

bull All electromagnetic radiation travels at All electromagnetic radiation travels at cc = 3 = 3101088 ms ms in in vacuum ndash vacuum ndash thethe cosmic speed limit cosmic speed limitndash real number is 2997924580 ms exactly

UCSD Physics 10

Spring 2008 7

Whatrsquos ldquoWavingrdquo in EM wavesWhatrsquos ldquoWavingrdquo in EM wavesbull What medium transports sound wavesWhat medium transports sound waves

ndash Can there be sound waves in the vacuum of outer space

bull What medium transports water wavesWhat medium transports water waves

bull What medium transports radio wavesWhat medium transports radio waves

bull A topic of considerable debate in the late 1800rsquos and early A topic of considerable debate in the late 1800rsquos and early 1900rsquos1900rsquos

bull Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible ldquojellordquo that was thought to vibrate electromagnetically ldquojellordquo that was thought to vibrate electromagnetically

bull Experiments that sought this ether didnrsquot find it Experiments that sought this ether didnrsquot find it

bull This was quite a surpriseThis was quite a surprise

Electromagnetic waves travel through empty space

UCSD Physics 10

Spring 2008 8

Whatrsquos ldquoWavingrdquo in EM wavesWhatrsquos ldquoWavingrdquo in EM wavesbull What medium transports sound waves What medium transports sound waves AirAir

ndash Can there be sound waves in the vacuum of outer space No

bull What medium transports water waves What medium transports water waves Water (fluids)Water (fluids)

bull What medium transports radio waves What medium transports radio waves AirAir

bull A topic of considerable debate in the late 1800rsquos and early A topic of considerable debate in the late 1800rsquos and early 1900rsquos1900rsquos

bull Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible ldquojellordquo that was thought to vibrate electromagnetically ldquojellordquo that was thought to vibrate electromagnetically

bull Experiments that sought this ether didnrsquot find it Experiments that sought this ether didnrsquot find it

bull This was quite a surpriseThis was quite a surprise

Electromagnetic waves travel through empty spaceNo medium required

UCSD Physics 10

Spring 2008 9

Examples of Electromagnetic RadiationExamples of Electromagnetic Radiation

bull AM and FM radio waves (including TV signals)AM and FM radio waves (including TV signals)ndash Cell phone communication links

bull MicrowavesMicrowavesbull Infrared radiationInfrared radiationbull Light Light bull Ultra-violet raysUltra-violet raysbull X-raysX-raysbull Gamma raysGamma raysbull Frequency distinguishes these from one anotherFrequency distinguishes these from one another

UCSD Physics 10

Spring 2008 10

Uses of Electromagnetic WavesUses of Electromagnetic Wavesbull Communication systems (radio)Communication systems (radio)

ndash One-way and two-way

ndash Radar

bull Cooking (microwaves)Cooking (microwaves)

bull ldquoldquoNight Visionrdquo or heat (infrared)Night Visionrdquo or heat (infrared)

bull Sun tanning (Ultra-violet)Sun tanning (Ultra-violet)

bull Medical Imaging (X rays)Medical Imaging (X rays)

bull Astronomy (radio Astronomy (radio wave IR visible light UV gamma)wave IR visible light UV gamma)

All that we experience through our eyes is conveyed byelectromagnetic radiationhellip

UCSD Physics 10

Spring 2008 11

The Electromagnetic SpectrumThe Electromagnetic Spectrum

bull Relationship between frequency speed and Relationship between frequency speed and wavelengthwavelength

f f = c = c ff is frequency is frequency is wavelength is wavelength cc is speed of light is speed of lightbull Different frequencies of electromagnetic radiation Different frequencies of electromagnetic radiation

are better suited to different purposesare better suited to different purposesbull The frequency of a radio wave determines its The frequency of a radio wave determines its

propagation characteristics through various mediapropagation characteristics through various media

UCSD Physics 10

Spring 2008 12

US Frequency Allocation ndash the FCCUS Frequency Allocation ndash the FCC

(300 MHz has a wavelength of 1 meter)

ldquoRadiordquo frequency-space is allocated to the hiltHerersquos a sample region from 300ndash600 MHz

International allocation gets tricky

UCSD Physics 10

Spring 2008 13

Generation of Radio WavesGeneration of Radio Waves

bull Accelerating charges radiate EM energyAccelerating charges radiate EM energybull If charges oscillate back and forth get time-varying fieldsIf charges oscillate back and forth get time-varying fields

E

+++

+

UCSD Physics 10

Spring 2008 14

Generation of Radio WavesGeneration of Radio Waves

If charges oscillate back and forth get time-varying magnetic fields tooIf charges oscillate back and forth get time-varying magnetic fields tooNote that the magnetic fields are perpendicular to the electric field vectorsNote that the magnetic fields are perpendicular to the electric field vectors

B

+++

+

UCSD Physics 10

Spring 2008 15

Polarization of Radio WavesPolarization of Radio Waves

B

ETransmitting antenna

UCSD Physics 10

Spring 2008 16

Reception of Radio WavesReception of Radio Waves

Receiving antenna works best when lsquotunedrsquo to the

wavelength of the signal and has proper polarization

Electrons in antenna are ldquojiggledrdquoby passage of electromagnetic wave

B

E

Optimal antenna length is one quarter-wavelength (4)

UCSD Physics 10

Spring 2008 5

The Electromagnetic ConnectionThe Electromagnetic Connection

bull A A changingchanging magnetic field produces an electric field and a magnetic field produces an electric field and a changing electric field produces a magnetic field changing electric field produces a magnetic field

bull Electric and Magnetic fields can produce forces on chargesElectric and Magnetic fields can produce forces on charges

bull An An acceleratingaccelerating charge produces electromagnetic waves charge produces electromagnetic waves (radiation)(radiation)

bull Both electric and magnetic fields can transport energyBoth electric and magnetic fields can transport energyndash Electric field energy used in electrical circuits eg released in

lightning

ndash Magnetic field carries energy through transformer for example

UCSD Physics 10

Spring 2008 6

Electromagnetic RadiationElectromagnetic Radiation

bull Interrelated electric and magnetic fields traveling through spaceInterrelated electric and magnetic fields traveling through space

bull All electromagnetic radiation travels at All electromagnetic radiation travels at cc = 3 = 3101088 ms ms in in vacuum ndash vacuum ndash thethe cosmic speed limit cosmic speed limitndash real number is 2997924580 ms exactly

UCSD Physics 10

Spring 2008 7

Whatrsquos ldquoWavingrdquo in EM wavesWhatrsquos ldquoWavingrdquo in EM wavesbull What medium transports sound wavesWhat medium transports sound waves

ndash Can there be sound waves in the vacuum of outer space

bull What medium transports water wavesWhat medium transports water waves

bull What medium transports radio wavesWhat medium transports radio waves

bull A topic of considerable debate in the late 1800rsquos and early A topic of considerable debate in the late 1800rsquos and early 1900rsquos1900rsquos

bull Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible ldquojellordquo that was thought to vibrate electromagnetically ldquojellordquo that was thought to vibrate electromagnetically

bull Experiments that sought this ether didnrsquot find it Experiments that sought this ether didnrsquot find it

bull This was quite a surpriseThis was quite a surprise

Electromagnetic waves travel through empty space

UCSD Physics 10

Spring 2008 8

Whatrsquos ldquoWavingrdquo in EM wavesWhatrsquos ldquoWavingrdquo in EM wavesbull What medium transports sound waves What medium transports sound waves AirAir

ndash Can there be sound waves in the vacuum of outer space No

bull What medium transports water waves What medium transports water waves Water (fluids)Water (fluids)

bull What medium transports radio waves What medium transports radio waves AirAir

bull A topic of considerable debate in the late 1800rsquos and early A topic of considerable debate in the late 1800rsquos and early 1900rsquos1900rsquos

bull Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible ldquojellordquo that was thought to vibrate electromagnetically ldquojellordquo that was thought to vibrate electromagnetically

bull Experiments that sought this ether didnrsquot find it Experiments that sought this ether didnrsquot find it

bull This was quite a surpriseThis was quite a surprise

Electromagnetic waves travel through empty spaceNo medium required

UCSD Physics 10

Spring 2008 9

Examples of Electromagnetic RadiationExamples of Electromagnetic Radiation

bull AM and FM radio waves (including TV signals)AM and FM radio waves (including TV signals)ndash Cell phone communication links

bull MicrowavesMicrowavesbull Infrared radiationInfrared radiationbull Light Light bull Ultra-violet raysUltra-violet raysbull X-raysX-raysbull Gamma raysGamma raysbull Frequency distinguishes these from one anotherFrequency distinguishes these from one another

UCSD Physics 10

Spring 2008 10

Uses of Electromagnetic WavesUses of Electromagnetic Wavesbull Communication systems (radio)Communication systems (radio)

ndash One-way and two-way

ndash Radar

bull Cooking (microwaves)Cooking (microwaves)

bull ldquoldquoNight Visionrdquo or heat (infrared)Night Visionrdquo or heat (infrared)

bull Sun tanning (Ultra-violet)Sun tanning (Ultra-violet)

bull Medical Imaging (X rays)Medical Imaging (X rays)

bull Astronomy (radio Astronomy (radio wave IR visible light UV gamma)wave IR visible light UV gamma)

All that we experience through our eyes is conveyed byelectromagnetic radiationhellip

UCSD Physics 10

Spring 2008 11

The Electromagnetic SpectrumThe Electromagnetic Spectrum

bull Relationship between frequency speed and Relationship between frequency speed and wavelengthwavelength

f f = c = c ff is frequency is frequency is wavelength is wavelength cc is speed of light is speed of lightbull Different frequencies of electromagnetic radiation Different frequencies of electromagnetic radiation

are better suited to different purposesare better suited to different purposesbull The frequency of a radio wave determines its The frequency of a radio wave determines its

propagation characteristics through various mediapropagation characteristics through various media

UCSD Physics 10

Spring 2008 12

US Frequency Allocation ndash the FCCUS Frequency Allocation ndash the FCC

(300 MHz has a wavelength of 1 meter)

ldquoRadiordquo frequency-space is allocated to the hiltHerersquos a sample region from 300ndash600 MHz

International allocation gets tricky

UCSD Physics 10

Spring 2008 13

Generation of Radio WavesGeneration of Radio Waves

bull Accelerating charges radiate EM energyAccelerating charges radiate EM energybull If charges oscillate back and forth get time-varying fieldsIf charges oscillate back and forth get time-varying fields

E

+++

+

UCSD Physics 10

Spring 2008 14

Generation of Radio WavesGeneration of Radio Waves

If charges oscillate back and forth get time-varying magnetic fields tooIf charges oscillate back and forth get time-varying magnetic fields tooNote that the magnetic fields are perpendicular to the electric field vectorsNote that the magnetic fields are perpendicular to the electric field vectors

B

+++

+

UCSD Physics 10

Spring 2008 15

Polarization of Radio WavesPolarization of Radio Waves

B

ETransmitting antenna

UCSD Physics 10

Spring 2008 16

Reception of Radio WavesReception of Radio Waves

Receiving antenna works best when lsquotunedrsquo to the

wavelength of the signal and has proper polarization

Electrons in antenna are ldquojiggledrdquoby passage of electromagnetic wave

B

E

Optimal antenna length is one quarter-wavelength (4)

UCSD Physics 10

Spring 2008 6

Electromagnetic RadiationElectromagnetic Radiation

bull Interrelated electric and magnetic fields traveling through spaceInterrelated electric and magnetic fields traveling through space

bull All electromagnetic radiation travels at All electromagnetic radiation travels at cc = 3 = 3101088 ms ms in in vacuum ndash vacuum ndash thethe cosmic speed limit cosmic speed limitndash real number is 2997924580 ms exactly

UCSD Physics 10

Spring 2008 7

Whatrsquos ldquoWavingrdquo in EM wavesWhatrsquos ldquoWavingrdquo in EM wavesbull What medium transports sound wavesWhat medium transports sound waves

ndash Can there be sound waves in the vacuum of outer space

bull What medium transports water wavesWhat medium transports water waves

bull What medium transports radio wavesWhat medium transports radio waves

bull A topic of considerable debate in the late 1800rsquos and early A topic of considerable debate in the late 1800rsquos and early 1900rsquos1900rsquos

bull Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible ldquojellordquo that was thought to vibrate electromagnetically ldquojellordquo that was thought to vibrate electromagnetically

bull Experiments that sought this ether didnrsquot find it Experiments that sought this ether didnrsquot find it

bull This was quite a surpriseThis was quite a surprise

Electromagnetic waves travel through empty space

UCSD Physics 10

Spring 2008 8

Whatrsquos ldquoWavingrdquo in EM wavesWhatrsquos ldquoWavingrdquo in EM wavesbull What medium transports sound waves What medium transports sound waves AirAir

ndash Can there be sound waves in the vacuum of outer space No

bull What medium transports water waves What medium transports water waves Water (fluids)Water (fluids)

bull What medium transports radio waves What medium transports radio waves AirAir

bull A topic of considerable debate in the late 1800rsquos and early A topic of considerable debate in the late 1800rsquos and early 1900rsquos1900rsquos

bull Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible ldquojellordquo that was thought to vibrate electromagnetically ldquojellordquo that was thought to vibrate electromagnetically

bull Experiments that sought this ether didnrsquot find it Experiments that sought this ether didnrsquot find it

bull This was quite a surpriseThis was quite a surprise

Electromagnetic waves travel through empty spaceNo medium required

UCSD Physics 10

Spring 2008 9

Examples of Electromagnetic RadiationExamples of Electromagnetic Radiation

bull AM and FM radio waves (including TV signals)AM and FM radio waves (including TV signals)ndash Cell phone communication links

bull MicrowavesMicrowavesbull Infrared radiationInfrared radiationbull Light Light bull Ultra-violet raysUltra-violet raysbull X-raysX-raysbull Gamma raysGamma raysbull Frequency distinguishes these from one anotherFrequency distinguishes these from one another

UCSD Physics 10

Spring 2008 10

Uses of Electromagnetic WavesUses of Electromagnetic Wavesbull Communication systems (radio)Communication systems (radio)

ndash One-way and two-way

ndash Radar

bull Cooking (microwaves)Cooking (microwaves)

bull ldquoldquoNight Visionrdquo or heat (infrared)Night Visionrdquo or heat (infrared)

bull Sun tanning (Ultra-violet)Sun tanning (Ultra-violet)

bull Medical Imaging (X rays)Medical Imaging (X rays)

bull Astronomy (radio Astronomy (radio wave IR visible light UV gamma)wave IR visible light UV gamma)

All that we experience through our eyes is conveyed byelectromagnetic radiationhellip

UCSD Physics 10

Spring 2008 11

The Electromagnetic SpectrumThe Electromagnetic Spectrum

bull Relationship between frequency speed and Relationship between frequency speed and wavelengthwavelength

f f = c = c ff is frequency is frequency is wavelength is wavelength cc is speed of light is speed of lightbull Different frequencies of electromagnetic radiation Different frequencies of electromagnetic radiation

are better suited to different purposesare better suited to different purposesbull The frequency of a radio wave determines its The frequency of a radio wave determines its

propagation characteristics through various mediapropagation characteristics through various media

UCSD Physics 10

Spring 2008 12

US Frequency Allocation ndash the FCCUS Frequency Allocation ndash the FCC

(300 MHz has a wavelength of 1 meter)

ldquoRadiordquo frequency-space is allocated to the hiltHerersquos a sample region from 300ndash600 MHz

International allocation gets tricky

UCSD Physics 10

Spring 2008 13

Generation of Radio WavesGeneration of Radio Waves

bull Accelerating charges radiate EM energyAccelerating charges radiate EM energybull If charges oscillate back and forth get time-varying fieldsIf charges oscillate back and forth get time-varying fields

E

+++

+

UCSD Physics 10

Spring 2008 14

Generation of Radio WavesGeneration of Radio Waves

If charges oscillate back and forth get time-varying magnetic fields tooIf charges oscillate back and forth get time-varying magnetic fields tooNote that the magnetic fields are perpendicular to the electric field vectorsNote that the magnetic fields are perpendicular to the electric field vectors

B

+++

+

UCSD Physics 10

Spring 2008 15

Polarization of Radio WavesPolarization of Radio Waves

B

ETransmitting antenna

UCSD Physics 10

Spring 2008 16

Reception of Radio WavesReception of Radio Waves

Receiving antenna works best when lsquotunedrsquo to the

wavelength of the signal and has proper polarization

Electrons in antenna are ldquojiggledrdquoby passage of electromagnetic wave

B

E

Optimal antenna length is one quarter-wavelength (4)

UCSD Physics 10

Spring 2008 7

Whatrsquos ldquoWavingrdquo in EM wavesWhatrsquos ldquoWavingrdquo in EM wavesbull What medium transports sound wavesWhat medium transports sound waves

ndash Can there be sound waves in the vacuum of outer space

bull What medium transports water wavesWhat medium transports water waves

bull What medium transports radio wavesWhat medium transports radio waves

bull A topic of considerable debate in the late 1800rsquos and early A topic of considerable debate in the late 1800rsquos and early 1900rsquos1900rsquos

bull Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible ldquojellordquo that was thought to vibrate electromagnetically ldquojellordquo that was thought to vibrate electromagnetically

bull Experiments that sought this ether didnrsquot find it Experiments that sought this ether didnrsquot find it

bull This was quite a surpriseThis was quite a surprise

Electromagnetic waves travel through empty space

UCSD Physics 10

Spring 2008 8

Whatrsquos ldquoWavingrdquo in EM wavesWhatrsquos ldquoWavingrdquo in EM wavesbull What medium transports sound waves What medium transports sound waves AirAir

ndash Can there be sound waves in the vacuum of outer space No

bull What medium transports water waves What medium transports water waves Water (fluids)Water (fluids)

bull What medium transports radio waves What medium transports radio waves AirAir

bull A topic of considerable debate in the late 1800rsquos and early A topic of considerable debate in the late 1800rsquos and early 1900rsquos1900rsquos

bull Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible ldquojellordquo that was thought to vibrate electromagnetically ldquojellordquo that was thought to vibrate electromagnetically

bull Experiments that sought this ether didnrsquot find it Experiments that sought this ether didnrsquot find it

bull This was quite a surpriseThis was quite a surprise

Electromagnetic waves travel through empty spaceNo medium required

UCSD Physics 10

Spring 2008 9

Examples of Electromagnetic RadiationExamples of Electromagnetic Radiation

bull AM and FM radio waves (including TV signals)AM and FM radio waves (including TV signals)ndash Cell phone communication links

bull MicrowavesMicrowavesbull Infrared radiationInfrared radiationbull Light Light bull Ultra-violet raysUltra-violet raysbull X-raysX-raysbull Gamma raysGamma raysbull Frequency distinguishes these from one anotherFrequency distinguishes these from one another

UCSD Physics 10

Spring 2008 10

Uses of Electromagnetic WavesUses of Electromagnetic Wavesbull Communication systems (radio)Communication systems (radio)

ndash One-way and two-way

ndash Radar

bull Cooking (microwaves)Cooking (microwaves)

bull ldquoldquoNight Visionrdquo or heat (infrared)Night Visionrdquo or heat (infrared)

bull Sun tanning (Ultra-violet)Sun tanning (Ultra-violet)

bull Medical Imaging (X rays)Medical Imaging (X rays)

bull Astronomy (radio Astronomy (radio wave IR visible light UV gamma)wave IR visible light UV gamma)

All that we experience through our eyes is conveyed byelectromagnetic radiationhellip

UCSD Physics 10

Spring 2008 11

The Electromagnetic SpectrumThe Electromagnetic Spectrum

bull Relationship between frequency speed and Relationship between frequency speed and wavelengthwavelength

f f = c = c ff is frequency is frequency is wavelength is wavelength cc is speed of light is speed of lightbull Different frequencies of electromagnetic radiation Different frequencies of electromagnetic radiation

are better suited to different purposesare better suited to different purposesbull The frequency of a radio wave determines its The frequency of a radio wave determines its

propagation characteristics through various mediapropagation characteristics through various media

UCSD Physics 10

Spring 2008 12

US Frequency Allocation ndash the FCCUS Frequency Allocation ndash the FCC

(300 MHz has a wavelength of 1 meter)

ldquoRadiordquo frequency-space is allocated to the hiltHerersquos a sample region from 300ndash600 MHz

International allocation gets tricky

UCSD Physics 10

Spring 2008 13

Generation of Radio WavesGeneration of Radio Waves

bull Accelerating charges radiate EM energyAccelerating charges radiate EM energybull If charges oscillate back and forth get time-varying fieldsIf charges oscillate back and forth get time-varying fields

E

+++

+

UCSD Physics 10

Spring 2008 14

Generation of Radio WavesGeneration of Radio Waves

If charges oscillate back and forth get time-varying magnetic fields tooIf charges oscillate back and forth get time-varying magnetic fields tooNote that the magnetic fields are perpendicular to the electric field vectorsNote that the magnetic fields are perpendicular to the electric field vectors

B

+++

+

UCSD Physics 10

Spring 2008 15

Polarization of Radio WavesPolarization of Radio Waves

B

ETransmitting antenna

UCSD Physics 10

Spring 2008 16

Reception of Radio WavesReception of Radio Waves

Receiving antenna works best when lsquotunedrsquo to the

wavelength of the signal and has proper polarization

Electrons in antenna are ldquojiggledrdquoby passage of electromagnetic wave

B

E

Optimal antenna length is one quarter-wavelength (4)

UCSD Physics 10

Spring 2008 8

Whatrsquos ldquoWavingrdquo in EM wavesWhatrsquos ldquoWavingrdquo in EM wavesbull What medium transports sound waves What medium transports sound waves AirAir

ndash Can there be sound waves in the vacuum of outer space No

bull What medium transports water waves What medium transports water waves Water (fluids)Water (fluids)

bull What medium transports radio waves What medium transports radio waves AirAir

bull A topic of considerable debate in the late 1800rsquos and early A topic of considerable debate in the late 1800rsquos and early 1900rsquos1900rsquos

bull Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible Led to the concept of the ldquoluminiferous etherrdquo ndash an invisible ldquojellordquo that was thought to vibrate electromagnetically ldquojellordquo that was thought to vibrate electromagnetically

bull Experiments that sought this ether didnrsquot find it Experiments that sought this ether didnrsquot find it

bull This was quite a surpriseThis was quite a surprise

Electromagnetic waves travel through empty spaceNo medium required

UCSD Physics 10

Spring 2008 9

Examples of Electromagnetic RadiationExamples of Electromagnetic Radiation

bull AM and FM radio waves (including TV signals)AM and FM radio waves (including TV signals)ndash Cell phone communication links

bull MicrowavesMicrowavesbull Infrared radiationInfrared radiationbull Light Light bull Ultra-violet raysUltra-violet raysbull X-raysX-raysbull Gamma raysGamma raysbull Frequency distinguishes these from one anotherFrequency distinguishes these from one another

UCSD Physics 10

Spring 2008 10

Uses of Electromagnetic WavesUses of Electromagnetic Wavesbull Communication systems (radio)Communication systems (radio)

ndash One-way and two-way

ndash Radar

bull Cooking (microwaves)Cooking (microwaves)

bull ldquoldquoNight Visionrdquo or heat (infrared)Night Visionrdquo or heat (infrared)

bull Sun tanning (Ultra-violet)Sun tanning (Ultra-violet)

bull Medical Imaging (X rays)Medical Imaging (X rays)

bull Astronomy (radio Astronomy (radio wave IR visible light UV gamma)wave IR visible light UV gamma)

All that we experience through our eyes is conveyed byelectromagnetic radiationhellip

UCSD Physics 10

Spring 2008 11

The Electromagnetic SpectrumThe Electromagnetic Spectrum

bull Relationship between frequency speed and Relationship between frequency speed and wavelengthwavelength

f f = c = c ff is frequency is frequency is wavelength is wavelength cc is speed of light is speed of lightbull Different frequencies of electromagnetic radiation Different frequencies of electromagnetic radiation

are better suited to different purposesare better suited to different purposesbull The frequency of a radio wave determines its The frequency of a radio wave determines its

propagation characteristics through various mediapropagation characteristics through various media

UCSD Physics 10

Spring 2008 12

US Frequency Allocation ndash the FCCUS Frequency Allocation ndash the FCC

(300 MHz has a wavelength of 1 meter)

ldquoRadiordquo frequency-space is allocated to the hiltHerersquos a sample region from 300ndash600 MHz

International allocation gets tricky

UCSD Physics 10

Spring 2008 13

Generation of Radio WavesGeneration of Radio Waves

bull Accelerating charges radiate EM energyAccelerating charges radiate EM energybull If charges oscillate back and forth get time-varying fieldsIf charges oscillate back and forth get time-varying fields

E

+++

+

UCSD Physics 10

Spring 2008 14

Generation of Radio WavesGeneration of Radio Waves

If charges oscillate back and forth get time-varying magnetic fields tooIf charges oscillate back and forth get time-varying magnetic fields tooNote that the magnetic fields are perpendicular to the electric field vectorsNote that the magnetic fields are perpendicular to the electric field vectors

B

+++

+

UCSD Physics 10

Spring 2008 15

Polarization of Radio WavesPolarization of Radio Waves

B

ETransmitting antenna

UCSD Physics 10

Spring 2008 16

Reception of Radio WavesReception of Radio Waves

Receiving antenna works best when lsquotunedrsquo to the

wavelength of the signal and has proper polarization

Electrons in antenna are ldquojiggledrdquoby passage of electromagnetic wave

B

E

Optimal antenna length is one quarter-wavelength (4)

UCSD Physics 10

Spring 2008 9

Examples of Electromagnetic RadiationExamples of Electromagnetic Radiation

bull AM and FM radio waves (including TV signals)AM and FM radio waves (including TV signals)ndash Cell phone communication links

bull MicrowavesMicrowavesbull Infrared radiationInfrared radiationbull Light Light bull Ultra-violet raysUltra-violet raysbull X-raysX-raysbull Gamma raysGamma raysbull Frequency distinguishes these from one anotherFrequency distinguishes these from one another

UCSD Physics 10

Spring 2008 10

Uses of Electromagnetic WavesUses of Electromagnetic Wavesbull Communication systems (radio)Communication systems (radio)

ndash One-way and two-way

ndash Radar

bull Cooking (microwaves)Cooking (microwaves)

bull ldquoldquoNight Visionrdquo or heat (infrared)Night Visionrdquo or heat (infrared)

bull Sun tanning (Ultra-violet)Sun tanning (Ultra-violet)

bull Medical Imaging (X rays)Medical Imaging (X rays)

bull Astronomy (radio Astronomy (radio wave IR visible light UV gamma)wave IR visible light UV gamma)

All that we experience through our eyes is conveyed byelectromagnetic radiationhellip

UCSD Physics 10

Spring 2008 11

The Electromagnetic SpectrumThe Electromagnetic Spectrum

bull Relationship between frequency speed and Relationship between frequency speed and wavelengthwavelength

f f = c = c ff is frequency is frequency is wavelength is wavelength cc is speed of light is speed of lightbull Different frequencies of electromagnetic radiation Different frequencies of electromagnetic radiation

are better suited to different purposesare better suited to different purposesbull The frequency of a radio wave determines its The frequency of a radio wave determines its

propagation characteristics through various mediapropagation characteristics through various media

UCSD Physics 10

Spring 2008 12

US Frequency Allocation ndash the FCCUS Frequency Allocation ndash the FCC

(300 MHz has a wavelength of 1 meter)

ldquoRadiordquo frequency-space is allocated to the hiltHerersquos a sample region from 300ndash600 MHz

International allocation gets tricky

UCSD Physics 10

Spring 2008 13

Generation of Radio WavesGeneration of Radio Waves

bull Accelerating charges radiate EM energyAccelerating charges radiate EM energybull If charges oscillate back and forth get time-varying fieldsIf charges oscillate back and forth get time-varying fields

E

+++

+

UCSD Physics 10

Spring 2008 14

Generation of Radio WavesGeneration of Radio Waves

If charges oscillate back and forth get time-varying magnetic fields tooIf charges oscillate back and forth get time-varying magnetic fields tooNote that the magnetic fields are perpendicular to the electric field vectorsNote that the magnetic fields are perpendicular to the electric field vectors

B

+++

+

UCSD Physics 10

Spring 2008 15

Polarization of Radio WavesPolarization of Radio Waves

B

ETransmitting antenna

UCSD Physics 10

Spring 2008 16

Reception of Radio WavesReception of Radio Waves

Receiving antenna works best when lsquotunedrsquo to the

wavelength of the signal and has proper polarization

Electrons in antenna are ldquojiggledrdquoby passage of electromagnetic wave

B

E

Optimal antenna length is one quarter-wavelength (4)

UCSD Physics 10

Spring 2008 10

Uses of Electromagnetic WavesUses of Electromagnetic Wavesbull Communication systems (radio)Communication systems (radio)

ndash One-way and two-way

ndash Radar

bull Cooking (microwaves)Cooking (microwaves)

bull ldquoldquoNight Visionrdquo or heat (infrared)Night Visionrdquo or heat (infrared)

bull Sun tanning (Ultra-violet)Sun tanning (Ultra-violet)

bull Medical Imaging (X rays)Medical Imaging (X rays)

bull Astronomy (radio Astronomy (radio wave IR visible light UV gamma)wave IR visible light UV gamma)

All that we experience through our eyes is conveyed byelectromagnetic radiationhellip

UCSD Physics 10

Spring 2008 11

The Electromagnetic SpectrumThe Electromagnetic Spectrum

bull Relationship between frequency speed and Relationship between frequency speed and wavelengthwavelength

f f = c = c ff is frequency is frequency is wavelength is wavelength cc is speed of light is speed of lightbull Different frequencies of electromagnetic radiation Different frequencies of electromagnetic radiation

are better suited to different purposesare better suited to different purposesbull The frequency of a radio wave determines its The frequency of a radio wave determines its

propagation characteristics through various mediapropagation characteristics through various media

UCSD Physics 10

Spring 2008 12

US Frequency Allocation ndash the FCCUS Frequency Allocation ndash the FCC

(300 MHz has a wavelength of 1 meter)

ldquoRadiordquo frequency-space is allocated to the hiltHerersquos a sample region from 300ndash600 MHz

International allocation gets tricky

UCSD Physics 10

Spring 2008 13

Generation of Radio WavesGeneration of Radio Waves

bull Accelerating charges radiate EM energyAccelerating charges radiate EM energybull If charges oscillate back and forth get time-varying fieldsIf charges oscillate back and forth get time-varying fields

E

+++

+

UCSD Physics 10

Spring 2008 14

Generation of Radio WavesGeneration of Radio Waves

If charges oscillate back and forth get time-varying magnetic fields tooIf charges oscillate back and forth get time-varying magnetic fields tooNote that the magnetic fields are perpendicular to the electric field vectorsNote that the magnetic fields are perpendicular to the electric field vectors

B

+++

+

UCSD Physics 10

Spring 2008 15

Polarization of Radio WavesPolarization of Radio Waves

B

ETransmitting antenna

UCSD Physics 10

Spring 2008 16

Reception of Radio WavesReception of Radio Waves

Receiving antenna works best when lsquotunedrsquo to the

wavelength of the signal and has proper polarization

Electrons in antenna are ldquojiggledrdquoby passage of electromagnetic wave

B

E

Optimal antenna length is one quarter-wavelength (4)

UCSD Physics 10

Spring 2008 11

The Electromagnetic SpectrumThe Electromagnetic Spectrum

bull Relationship between frequency speed and Relationship between frequency speed and wavelengthwavelength

f f = c = c ff is frequency is frequency is wavelength is wavelength cc is speed of light is speed of lightbull Different frequencies of electromagnetic radiation Different frequencies of electromagnetic radiation

are better suited to different purposesare better suited to different purposesbull The frequency of a radio wave determines its The frequency of a radio wave determines its

propagation characteristics through various mediapropagation characteristics through various media

UCSD Physics 10

Spring 2008 12

US Frequency Allocation ndash the FCCUS Frequency Allocation ndash the FCC

(300 MHz has a wavelength of 1 meter)

ldquoRadiordquo frequency-space is allocated to the hiltHerersquos a sample region from 300ndash600 MHz

International allocation gets tricky

UCSD Physics 10

Spring 2008 13

Generation of Radio WavesGeneration of Radio Waves

bull Accelerating charges radiate EM energyAccelerating charges radiate EM energybull If charges oscillate back and forth get time-varying fieldsIf charges oscillate back and forth get time-varying fields

E

+++

+

UCSD Physics 10

Spring 2008 14

Generation of Radio WavesGeneration of Radio Waves

If charges oscillate back and forth get time-varying magnetic fields tooIf charges oscillate back and forth get time-varying magnetic fields tooNote that the magnetic fields are perpendicular to the electric field vectorsNote that the magnetic fields are perpendicular to the electric field vectors

B

+++

+

UCSD Physics 10

Spring 2008 15

Polarization of Radio WavesPolarization of Radio Waves

B

ETransmitting antenna

UCSD Physics 10

Spring 2008 16

Reception of Radio WavesReception of Radio Waves

Receiving antenna works best when lsquotunedrsquo to the

wavelength of the signal and has proper polarization

Electrons in antenna are ldquojiggledrdquoby passage of electromagnetic wave

B

E

Optimal antenna length is one quarter-wavelength (4)

UCSD Physics 10

Spring 2008 12

US Frequency Allocation ndash the FCCUS Frequency Allocation ndash the FCC

(300 MHz has a wavelength of 1 meter)

ldquoRadiordquo frequency-space is allocated to the hiltHerersquos a sample region from 300ndash600 MHz

International allocation gets tricky

UCSD Physics 10

Spring 2008 13

Generation of Radio WavesGeneration of Radio Waves

bull Accelerating charges radiate EM energyAccelerating charges radiate EM energybull If charges oscillate back and forth get time-varying fieldsIf charges oscillate back and forth get time-varying fields

E

+++

+

UCSD Physics 10

Spring 2008 14

Generation of Radio WavesGeneration of Radio Waves

If charges oscillate back and forth get time-varying magnetic fields tooIf charges oscillate back and forth get time-varying magnetic fields tooNote that the magnetic fields are perpendicular to the electric field vectorsNote that the magnetic fields are perpendicular to the electric field vectors

B

+++

+

UCSD Physics 10

Spring 2008 15

Polarization of Radio WavesPolarization of Radio Waves

B

ETransmitting antenna

UCSD Physics 10

Spring 2008 16

Reception of Radio WavesReception of Radio Waves

Receiving antenna works best when lsquotunedrsquo to the

wavelength of the signal and has proper polarization

Electrons in antenna are ldquojiggledrdquoby passage of electromagnetic wave

B

E

Optimal antenna length is one quarter-wavelength (4)

UCSD Physics 10

Spring 2008 13

Generation of Radio WavesGeneration of Radio Waves

bull Accelerating charges radiate EM energyAccelerating charges radiate EM energybull If charges oscillate back and forth get time-varying fieldsIf charges oscillate back and forth get time-varying fields

E

+++

+

UCSD Physics 10

Spring 2008 14

Generation of Radio WavesGeneration of Radio Waves

If charges oscillate back and forth get time-varying magnetic fields tooIf charges oscillate back and forth get time-varying magnetic fields tooNote that the magnetic fields are perpendicular to the electric field vectorsNote that the magnetic fields are perpendicular to the electric field vectors

B

+++

+

UCSD Physics 10

Spring 2008 15

Polarization of Radio WavesPolarization of Radio Waves

B

ETransmitting antenna

UCSD Physics 10

Spring 2008 16

Reception of Radio WavesReception of Radio Waves

Receiving antenna works best when lsquotunedrsquo to the

wavelength of the signal and has proper polarization

Electrons in antenna are ldquojiggledrdquoby passage of electromagnetic wave

B

E

Optimal antenna length is one quarter-wavelength (4)

UCSD Physics 10

Spring 2008 14

Generation of Radio WavesGeneration of Radio Waves

If charges oscillate back and forth get time-varying magnetic fields tooIf charges oscillate back and forth get time-varying magnetic fields tooNote that the magnetic fields are perpendicular to the electric field vectorsNote that the magnetic fields are perpendicular to the electric field vectors

B

+++

+

UCSD Physics 10

Spring 2008 15

Polarization of Radio WavesPolarization of Radio Waves

B

ETransmitting antenna

UCSD Physics 10

Spring 2008 16

Reception of Radio WavesReception of Radio Waves

Receiving antenna works best when lsquotunedrsquo to the

wavelength of the signal and has proper polarization

Electrons in antenna are ldquojiggledrdquoby passage of electromagnetic wave

B

E

Optimal antenna length is one quarter-wavelength (4)

UCSD Physics 10

Spring 2008 15

Polarization of Radio WavesPolarization of Radio Waves

B

ETransmitting antenna

UCSD Physics 10

Spring 2008 16

Reception of Radio WavesReception of Radio Waves

Receiving antenna works best when lsquotunedrsquo to the

wavelength of the signal and has proper polarization

Electrons in antenna are ldquojiggledrdquoby passage of electromagnetic wave

B

E

Optimal antenna length is one quarter-wavelength (4)

UCSD Physics 10

Spring 2008 16

Reception of Radio WavesReception of Radio Waves

Receiving antenna works best when lsquotunedrsquo to the

wavelength of the signal and has proper polarization

Electrons in antenna are ldquojiggledrdquoby passage of electromagnetic wave

B

E

Optimal antenna length is one quarter-wavelength (4)