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Old February 28th 06, 10:59 AM posted to rec.radio.amateur.policy,rec.radio.amateur.misc
N9OGL
 
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Default Electromagnetic Radiation

From Discussion group: Amateur Radio Experimentation


Electromagnetic radiation is a propagating wave in space with electric
and magnetic components. These components oscillate at right angles to
each other and to the direction of propagation. The term
electromagnetic radiation is also used as a synonym for electromagnetic

waves in general, even if they are not radiating or travelling in free
space. This sense includes, for example, light travelling through an
optical fiber, or electrical energy travelling within a coaxial cable.
Electromagnetic (EM) radiation carries energy and momentum which may be

imparted when it interacts with matter.

PhysicsTheory
Electromagnetic waves of much lower frequency than visible light were
predicted by Maxwell's equations and subsequently discovered by
Heinrich Hertz. Maxwell derived a wave form of the electric and
magnetic equations which made explicit the wave nature of the electric
and magnetic fields. These equations displayed the symmetry of the
fields. According to the theory, a time-varying electric field
generates a magnetic field and vice versa. Thus, an oscillating
electric field creates an oscillating magnetic field, which in turn
creates an oscillating electric field, and so on. By this means an EM
wave is produced which propagates through space.
Properties Electric and magnetic fields exhibit the property of
superposition. This means that the field due to a particular particle
or time-varying electric or magnetic field adds to the fields due to
other causes. (As magnetic and electric fields are vector fields, this
is the vector addition of all the individual electric and magnetic
field vectors.) As a result, EM radiation is influenced by various
phenomena such as refraction and diffraction. For example, a travelling

EM wave incident on a particular arrangement of atoms induces
oscillation in the atoms and thus causes them to emit their own EM
waves. These emissions interfere with the impinging wave and alter its
form. In refraction, a wave moving from one medium to another of a
different density changes its speed and direction when it enters the
new medium. The ratio of the refractive indices of the media determines

the extent of refraction. Refraction is the mechanism by which light
disperses into a spectrum when it is shone through a prism. The physics

of electromagnetic radiation is electrodynamics, a subfield of
electromagnetism. EM radiation exhibits both wave properties and
particle properties at the same time (see wave-particle duality). These

characteristics are mutually exclusive and appear separately in
different circumstances: the wave characteristics appear when EM
radiation is measured over relatively large timescales and over large
distances, and the particle characteristics are evident when measuring
small distances and timescales. These characteristics have been
confirmed by a large number of experiments.
Wave model An important aspect of the wave nature of light is
frequency. The frequency of a wave is its rate of oscillation and is
measured in hertz, the SI unit of frequency, equal to one oscillation
per second. Light usually comprises a spectrum of frequencies which sum

to form the resultant wave. In addition, frequency affects properties
like refraction, in which different frequencies undergo a different
level of refraction. A wave has troughs and crests. The wavelength is
the distance from crest to crest. Waves in the electromagnetic spectrum

vary in size from very long radio waves the size of buildings, to very
short gamma-rays smaller than the size of the nucleus of an atom.
Frequency has an inverse relationship to the concept of wavelength.
When waves travel from one medium to another, their frequency remains
exactly the same - only their speed changes. Waves can also be
described by their radiant energy. Interference is the superposition of

two or more waves resulting in a new wave pattern. The way that these
coincide causes different types of interference.
Particle model In the particle model of EM radiation, EM radiation is
quantized as particles called photons. Quantisation of light represents

the discrete packets of energy which constitute the radiation. The
frequency of the radiation determines the magnitude of the energy of
the particles. Moreover, these particles are emitted and absorbed by
charged particles, so photons act as transporters of energy. A photon
absorbed by an atom excites an electron and elevates it to a higher
energy level. If the energy is great enough, the electron is liberated
from the atom in a process called ionization. Conversely, an electron
which descends to a lower energy level in an atom emits a photon of
light equal to the energy difference. The energy levels of electrons in

atoms are discrete. Therefore, each element has its own characteristic
frequencies. Together these effects explain the absorption spectra of
light. The dark bands in the spectrum are due to the atoms in the
intervening medium which absorb different frequencies of the light. The

composition of the medium through which the light travels determines
the nature of the absorption spectrum. For instance, in a distant star,

dark bands in the light it emits are due to the atoms in the atmosphere

of the star. These bands correspond to the allowed energy levels in the

atoms. A similar phenomenon occurs for emission. As the electrons
descend to lower energy levels, a spectrum which represents the jumps
between the energy levels of the electrons is exhibited. This is
manifested in the emission spectrum of nebulae.
Speed of propagation Any electric charge which accelerates, or any
changing magnetic field, produces electromagnetic radiation.
Electromagnetic information about the charge travels at the speed of
light. Accurate treatment thus incorporates a concept known as retarded

time (as opposed to advanced time, which is unphysical in light of
causality), which adds to the expressions for the electrodynamic
electric field and magnetic field. These extra terms are responsible
for electromagnetic radiation. When any wire (or other conducting
object such as an antenna) conducts alternating current,
electromagnetic radiation is propagated at the same frequency as the
electric current. Depending on the circumstances, it may behave as a
wave or as particles. As a wave, it is characterized by a velocity (the

speed of light), wavelength, and frequency. When considered as
particles, they are known as photons, and each has an energy related to

the frequency of the wave given by Planck's relation E = h?, where E is

the energy of the photon, h = 6.626 × 10-34 J·s is Planck's constant,

and ? is the frequency of the wave. One rule is always obeyed
regardless of the circumstances. EM radiation in a vacuum always
travels at the speed of light, relative to the observer, regardless of
the observer's velocity. (This observation led to Albert Einstein's
development of the theory of special relativity.) In a medium (other
than vacuum), velocity of propagation or refractive index are
considered, depending on frequency and application. Both of these are
ratios of the speed in a medium to speed in a vacuum.
Electromagnetic spectrum

Legend:
? = Gamma rays
HX = Hard X-rays
SX = Soft X-Rays
EUV = Extreme ultraviolet
NUV = Near ultravioletVisible light
NIR = Near infrared
MIR = Moderate infrared
FIR = Far infrared
Radio waves:
EHF = Extremely high frequency (Microwaves)
SHF = Super high frequency (Microwaves)
UHF = Ultrahigh frequency
VHF = Very high frequency
HF = High frequency
MF = Medium frequency
LF = Low frequency
VLF = Very low frequency
VF = Voice frequency
ELF = Extremely low frequency

Generally, EM radiation is classified by wavelength into electrical
energy, radio, microwave, infrared, the visible region we perceive as
light, ultraviolet, X-rays and gamma rays. The behavior of EM radiation

depends on its wavelength. Higher frequencies have shorter wavelengths,

and lower frequencies have longer wavelengths. When EM radiation
interacts with single atoms and molecules, its behavior depends on the
amount of energy per quantum it carries. Spectroscopy can detect a much

wider region of the EM spectrum than the visible range of 400 nm to 700

nm. A common laboratory spectroscope can detect wavelengths from 2 nm
to 2500 nm. More in-depth information about the physical properties of
objects, gases, or even stars can be obtained from this type of device.

It is widely used in astrophysics. For example, many hydrogen atoms
emit radio waves which have a wavelength of 21.12 cm.
Light Main article: light EM radiation with a wavelength between
approximately 400 nm and 700 nm is detected by the human eye and
perceived as visible light. If radiation having a frequency in the
visible region of the EM spectrum shines on an object, say, a bowl of
fruit, this results in our visual perception of identifying information

from the scene. Our brain's visual system processes the multitude of
reflected frequencies into different shades and hues, and through this
not-entirely-understood "psychophysical phenomenon," most humans
perceive a bowl of fruit. In the vast majority of cases, however, the
information carried by light is not directly apprehensible by human
senses. Natural sources produce EM radiation across the spectrum; so,
too, can human technology manipulate a broad range of wavelengths.
Optical fiber transmits light which, although not suitable for direct
viewing, can carry data. Those data can be translated into sound or an
image. The coded form of such data is similar to that used with radio
waves.

Radio waves Main article: radio wave Radio waves carry information by
varying amplitude and by varying frequency within a frequency band.
When EM radiation impinges upon a conductor, it couples to the
conductor, travels along it, and induces an electric current on the
surface of that conductor by exciting the electrons of the conducting
material. This effect (the skin effect) is used in antennas. EM
radiation may also cause certain molecules to absorb energy and thus to

heat up; this is exploited in microwave ovens.

Derivation Electromagnetic waves as a general phenomenon were predicted

by the classical laws of electricity and magnetism, known as Maxwell's
equations. If you inspect Maxwell's equations without sources (charges
or currents) then you will find that, along with the possibility of
nothing happening, the theory will also admit nontrivial solutions of
changing electric and magnetic fields. (For symbol definitions see
magnetic field.) is a solution, but there might be other solutions as
well. Let us employ a useful identity from vector calculus. Where can
be any vector function. Taking the curl of the curl equations and
applying the identity, we get the following. These types of equations
are identified as linear wave equations with wave speed . Amazingly,
this speed happens to be exactly the speed of light! Maxwell's
equations have unified the permittivity of free space ?0, the
permeability of free space ?0, and the speed of light itself: . Before
this derivation it was not known that there was such a strong
relationship between light and electricity and magnetism. But these are

only two equations and we started with four, so there is still more
information pertaining to these waves hidden within Maxwell's
equations. Let's consider a generic vector wave for the electric field.

Here is the constant amplitude, f is any second differentiable
function, is a unit vector in the direction of propagation, and is a
position vector. We observe that is a generic solution to the wave
equation. In other words, for a generic wave traveling in the
direction. The proof of this is trivial. This form will satisfy the
wave equation, but will it satisfy all of Maxwell's equations, and with

what corresponding magnetic field? The first of Maxell's equations
implies that electric field is orthogonal to the direction the wave
propagates. The second of Maxwell's equations yields the magnetic
field. The remaining equations will be satisfied by this choice of .
Not only are the electric and magnetic field waves traveling at the
speed of light, but they have a special restricted orientation and
proportional magnitudes, . The electric field, magnetic field, and
direction of wave propagation are all orthogonal and the wave
propagates in the same direction as . Visualizing yourself as an
electromagnetic wave traveling forward, the electric field might be
oscillating up and down, while the magnetic field oscillates right and
left; but you can rotate this picture around with the electric field
oscillating right and left and the magnetic field oscillating down and
up. This is a different solution that is traveling in the same
direction. This arbitrariness in the orientation, with respect to
propagation direction, is known as polarization.

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Old February 28th 06, 01:38 PM posted to rec.radio.amateur.policy,rec.radio.amateur.misc
 
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Default Electromagnetic Radiation


On 28 Feb 2006 01:59:58 -0800, N9OGL plagiarized:
From Discussion group: Amateur Radio Experimentation



Electromagnetic radiation is a propagating wave in space with electric

[240 lines snipped]

It isn't ethical to post someone else's work without giving them
credit for it. There's no way you wrote that, Toad; no way. You
are a plagiarizing bitch.
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Old February 28th 06, 02:31 PM posted to rec.radio.amateur.policy,rec.radio.amateur.misc
N9OGL
 
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Default Electromagnetic Radiation

You be suprised dumb ass what I can write, I'm a hell of lot smarter
then you dumb ass

Todd N9OGL

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Old February 28th 06, 02:38 PM posted to rec.radio.amateur.policy,rec.radio.amateur.misc
N9OGL
 
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Default Electromagnetic Radiation

And by the way dumb ass, that's general information, which if you knew
anything about Copyright Law is NOT COPYRIGHTABLE.....YOU DUMB ASS!!!



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Old February 28th 06, 02:43 PM posted to rec.radio.amateur.policy,rec.radio.amateur.misc
N0VFP
 
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Default Electromagnetic Radiation


N9OGL wrote:
You be suprised dumb ass what I can write, I'm a hell of lot smarter
then you dumb ass


You sure don't show it, dumbass. If you were smarter, you'd know where
to place commas and other punctuation, dimwit.

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Old February 28th 06, 02:44 PM posted to rec.radio.amateur.policy,rec.radio.amateur.misc
N0VFP
 
Posts: n/a
Default Electromagnetic Radiation


N9OGL wrote:
And by the way dumb ass, that's general information, which if you knew
anything about Copyright Law is NOT COPYRIGHTABLE.....YOU DUMB ASS!!!


You are ignorant about copyright law as you are with everything else,
idiot.

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Old February 28th 06, 02:58 PM posted to rec.radio.amateur.policy,rec.radio.amateur.misc
Lloyd
 
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Default Electromagnetic Radiation (ripped off from someone else)

On 28 Feb 2006 05:38:47 -0800, N9OGL wrote:
And by the way dumb ass, that's general information, which if you knew
anything about Copyright Law is NOT COPYRIGHTABLE.....YOU DUMB ASS!!!


But the copyright is on the work itself (the prose); not on the
information! I would suggest that it is you who hasn't the foggiest
understanding of copyright law.


----
God said, "div D = rho, div B = 0, curl E = -@B/@t, curl H = J + @D/@t,"
and then there was light.
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Old February 28th 06, 03:06 PM posted to rec.radio.amateur.policy,rec.radio.amateur.misc
N9OGL
 
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Default Electromagnetic Radiation (ripped off from someone else)

I beg to differ, the courts have ruled a number of times that data, is
not copyrightable. One case comes to mine had to do with a phone book a
telephone company had put out and another company copied it from word
to word and the phone company sued for copyright violation and the
supreme court ruled that general data, no matter how you write it is
not copyrightable.

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Old February 28th 06, 03:27 PM posted to rec.radio.amateur.policy,rec.radio.amateur.misc
Lloyd
 
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Default Electromagnetic Radiation (ripped off from someone else)

On 28 Feb 2006 06:06:12 -0800, N9OGL wrote:
I beg to differ, the courts have ruled a number of times that data, is
not copyrightable. One case comes to mine had to do with a phone book a
telephone company had put out and another company copied it from word
to word and the phone company sued for copyright violation and the
supreme court ruled that general data, no matter how you write it is
not copyrightable.


(*shrug*)

Tables of numbers do not constitute prose. What you ripped off does.
Try to reproduce a college text and distribute it, and see how long
it takes you to be hauled into court by its publisher.



----
God said, "div D = rho, div B = 0, curl E = -@B/@t, curl H = J + @D/@t,"
and then there was light.
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