electromagnetic spectrum basics

Copyright © 2007 by H. Paul Shuch, Ph.D. All Rights Reserved

ElectromagneticSpectrum Basics

H. Paul ShuchH. Paul Shuch

Visiting Professor of Physics and AstronomyVisiting Professor of Physics and Astronomy

Lycoming CollegeLycoming College


Lesson Objectives

Upon completion of this lesson, you will Upon completion of this lesson, you will demonstrate mastery by: demonstrate mastery by: • Deriving and recalling the speed of light Deriving and recalling the speed of light • Identifying the frequencies and wavelengths Identifying the frequencies and wavelengths defining the RF, Microwave, and visible spectra defining the RF, Microwave, and visible spectra • Converting between frequency and wavelengthConverting between frequency and wavelength• Knowing Planck's Constant from memory Knowing Planck's Constant from memory • Calculating the energy and mass of a photonCalculating the energy and mass of a photon


All waves behaveFundamentallyAlike GaussGauss

FaradayFaraday

AmpereAmpere


A continuum -- DC to Daylight . . .

and Beyond!


Visible Light

Less than one octave


= Frequency:Cycles per Second (Hz)

= Wavelength:Meters per Cycle


c =

Speed of Light


c = (both equal 3 * 108 m/s!)

Red: 750 nm * 400 THzViolet: 400 nm * 750 THz


(or three hundred kilometers per millisecond)

(that’s three hundred million meters per second)


The long and the short of it

The Rest of the Spectrum


The RF Spectrum

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RF Frequencies

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3 30 300 3 30 300 3 30 300 3 30 3003 30 300 3 30 300 3 30 300 3 30 300

Hz Hz Hz kHz kHz kHz MHz MHz MHz GHz GHz GHzHz Hz Hz kHz kHz kHz MHz MHz MHz GHz GHz GHz


RF Wavelengths

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100 10 1 100 10 1 100 10 1 10 1 1100 10 1 100 10 1 100 10 1 10 1 1

Mm Mm Mm km km km m m m cm cm mmMm Mm Mm km km km m m m cm cm mm m) = m) = 300 / 300 / (MHz)(MHz)


KuKu mmmmLL SS CC XX

1 GHz 100 GHz1 GHz 100 GHzLumped Lumped

ComponentsComponents

Distributed Distributed


Optical Optical


Microwave Bands



GHz: 1 2 4 8 12 18 100GHz: 1 2 4 8 12 18 100

Microwave Bands



cm: 30 15 7.5 3.75 2.5 1.67 0.3cm: 30 15 7.5 3.75 2.5 1.67 0.3

cm) cm) = 30 / = 30 / (GHz)(GHz)

GHz: 1 2 4 8 12 18 100GHz: 1 2 4 8 12 18 100

Microwave Bands


Microwave Band’sGreatest Hits


Actually, both!

Photons: are they waves, or particles?


Where h = 6.626 * 10-34 Joules * seconds

Energy per Photon –Planck’s Law

e = h


Remember red light?energy per photon

e = h * νe = (6.626 * 10-34 J * s) * (400 * 1012 cycles/s)e = 2.65 * 10-19 Joules


How about violet?energy per photon

e = h * νe = (6.626 * 10-34 J * s) * (750 * 1012 cycles/s)e = 4.97 * 10-19 Joules


How much energyper visible photon?

Less than a billionth of a billionth of a Joule!


Sunlight falling on Earth: ~ 1 kW/m2

(billions and billions of photons per secondper square meter!)


Left to right,Low to high energies

The spectrum asAn energy continuum


Q: How are Photonslike quick Catholics?

A: They have relativistic mass!A: They have relativistic mass!


(OK, so the rest mass of a photon is zero. However…)

e = h and e = m c2

so, h = m c2

and relativistic mass: m = h/c2


Let’s calculate relativistic mass for a red photon:

m = h/c2

= (6.626 * 10-34 J * s) * (400 * 1012 Hz) (3 * 108 m/s)2

= 2.94 * 10-36 kg


Is a red photon massive?

(no, that’s only about a millionth of the mass of an electron!)


Review Review ExercisesExercises


1. What is the velocity of forward propagation of radiant electromagnetic energy in free space?

c = 3 * 10c = 3 * 1088 m/s m/s


2. From memory, what frequencies and wave-lengths define the edges of the visible light spectrum? = 400 - 750 THz= 400 - 750 THz

= 750 - 400 nm= 750 - 400 nm


3. What is the value of Planck's Constant?

h = 6.626 * 10h = 6.626 * 10-34-34 J*s J*s


4. Interstellar hydrogen emits a strong spectral radiation line at a wavelength of 21 cm. To what frequency does this correspond? = c / = c /

= 1420 MHz= 1420 MHz


5. Interstellar hydrogen emits a strong spectral radiation line in which segment of the electromagnetic spectrum?1420 MHz is in the UHF spectrum, 1420 MHz is in the UHF spectrum, which extends from 300 to 3000 MHz.which extends from 300 to 3000 MHz.


6. Interstellar hydrogen emits a strong spectral radiation line in which microwave band?

21 cm is in L-band, which extends 21 cm is in L-band, which extends from 30 to 15 cm wavelength.from 30 to 15 cm wavelength.


7. Hydrogen line receiving equipment would be composed of which type of components?

All microwave circuitry incorporates All microwave circuitry incorporates distributed components.distributed components.


8. How much energy is emitted by one hydrogen photon? e = h * ν

e = (6.626 * 10-34 J*s) * (1.420 * 109 Hz)e = 9.4 * 10e = 9.4 * 10-25-25 Joules Joules


9. How much does that hydrogen photon weigh?

m = h/c2

= (6.626 * 10-34 J * s) * (1.42 * 109 Hz) (3 * 108 m/s)2

= 1.05 * 10-41 kg


10. What is the most important characteristic of all electromagnetic waves?

They all behave fundamentally alike.


Did you score eight or higher?

You’ve mastered You’ve mastered spectrum basics!spectrum basics!

electromagnetic spectrum basics

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