| Topic: |
Science > Physics |
| User: |
"Nomed" |
| Date: |
21 Jan 2007 10:22:12 AM |
| Object: |
Interaction of EM radiation with matter |
I would like to know how EM radiation (in the vicinity of the visible
spectrum) interacts with matter to give us the phenomena of reflection,
refraction, etc ...
I want to understand this at the most fundamental level, and not in the
high level abstraction of classical optics.
For example, when photons of light "strike" a reflective surface do
they simply "bounce" off the atoms (as I've been told!), or are they
absorbed and re-emitted? How long does this process take?
Assuming the later is correct, how is light incident at X degrees
reflected at 180-X degrees, i.e., how are the photons re-emitted at
180-X degrees? Is all non-direct light (i.e., reflected light)
ultimately re-emitted photons from light-matter interactions? Is this
light re-emitted at the same frequencies as the incident photons?
I'd imagine quantum mechanics equations are required to answer these
questions, so a pointer to a suitable web resource would be useful.
I've tried in vain to find such a source.
Thanks.
.
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| User: "OG" |
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| Title: Re: Interaction of EM radiation with matter |
21 Jan 2007 04:48:18 PM |
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"Nomed" <querygroup@gmail.com> wrote in message
news:1169396532.724841.319790@m58g2000cwm.googlegroups.com...
I would like to know how EM radiation (in the vicinity of the visible
spectrum) interacts with matter to give us the phenomena of reflection,
refraction, etc ...
I want to understand this at the most fundamental level, and not in the
high level abstraction of classical optics.
For example, when photons of light "strike" a reflective surface do
they simply "bounce" off the atoms (as I've been told!), or are they
absorbed and re-emitted? How long does this process take?
Assuming the later is correct, how is light incident at X degrees
reflected at 180-X degrees, i.e., how are the photons re-emitted at
180-X degrees? Is all non-direct light (i.e., reflected light)
ultimately re-emitted photons from light-matter interactions? Is this
light re-emitted at the same frequencies as the incident photons?
I'd imagine quantum mechanics equations are required to answer these
questions, so a pointer to a suitable web resource would be useful.
I've tried in vain to find such a source.
Thanks.
You will find the following invaluable
http://www.vega.org.uk/video/subseries/8
"A set of four priceless archival recordings from the University of Auckland
(New Zealand) of the outstanding Nobel prize-winning physicist Richard
Feynman - arguably the greatest science lecturer ever. Although the
recording is of modest technical quality the exceptional personal style and
unique delivery shine through"
The first two will tell you much about the question you are asking; probably
not everything, but enough to make sure you are asking the right questions.
.
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| User: "Edward Green" |
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| Title: Re: Interaction of EM radiation with matter |
21 Jan 2007 05:48:22 PM |
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OG wrote:
You will find the following invaluable
http://www.vega.org.uk/video/subseries/8
"A set of four priceless archival recordings from the University of Auckland
(New Zealand) of the outstanding Nobel prize-winning physicist Richard
Feynman - arguably the greatest science lecturer ever. Although the
recording is of modest technical quality the exceptional personal style and
unique delivery shine through"
What on earth is ".rm" format? My browser doesn't know how to play
the videos...
"yes, the realmedia is problematic. any corporation that only allows
one particular product to run on their own machine is what lawyers like
to call a monopoly, and it's absurd when you look at all the formats
available, and how much better these other, more flexible formats can
be. to point out the ridiculousness of it all, it would be as if GM or
Chrysler or Ford each required their own brands of gasoline, oil,
tires, etc.---and only their own brands---to be used with their
vehicles. not only this, but real's video backward compatibility is
heavily flawed, and their older players seem deliberately bugged to
remove common button and user features, all the better to get you to
download their newest product. again, an analogy: planned obsolescence.
and how does something called "real audio" turn out to be a video
format? were they paying attention in school? or just dreaming up ways
to rip off the public?"
http://www.greenspun.com/bboard/q-and-a-fetch-msg.tcl?msg_id=009Ojr
Oh. :-/ _That_ damn media player.
Why in the name of Feynman would a kind of non-profit educationally
flavored organization choose this proprietary format to encode their
"four priceless archival recordings". I hate media players in general
as a species -- they all want to preempt all your formats and bombard
you with unwanted "content" when you download them. A pox on all their
houses.
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| User: "OG" |
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| Title: Re: Interaction of EM radiation with matter |
21 Jan 2007 06:17:57 PM |
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"Edward Green" <spamspamspam3@netzero.com> wrote in message
news:1169423302.676710.160990@38g2000cwa.googlegroups.com...
OG wrote:
You will find the following invaluable
http://www.vega.org.uk/video/subseries/8
"A set of four priceless archival recordings from the University of
Auckland
(New Zealand) of the outstanding Nobel prize-winning physicist Richard
Feynman - arguably the greatest science lecturer ever. Although the
recording is of modest technical quality the exceptional personal style
and
unique delivery shine through"
What on earth is ".rm" format? My browser doesn't know how to play
the videos...
Oh. :-/ _That_ damn media player.
Why in the name of Feynman would a kind of non-profit educationally
flavored organization choose this proprietary format to encode their
"four priceless archival recordings". I hate media players in general
as a species -- they all want to preempt all your formats and bombard
you with unwanted "content" when you download them. A pox on all their
houses.
Why .rm ? No idea, except that compression is not bad and it's possible they
hoped that it would be easier to keep them from being downloaded as files (I
know it can be done, but its not quite as simple as right click, Save Target
as. . .).
I think it used to be the case that the BBC website offered a specially
tailored version of Real Player that was less annoying than the standard
one. I can't guarantee that this will work for you (particularly if you live
outside UK), but you could start from here.
http://www.bbc.co.uk/webwise/categories/plug/real/newreal.shtml?newintro
Alternatively, you can try
RealAlternative
(No idea of the url, I'm very happy with Real Player as provided above).
Notwithstanding all that, the lectures are well worth viewing.
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| User: "Edward Green" |
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| Title: Re: Interaction of EM radiation with matter |
22 Jan 2007 12:42:07 AM |
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OG wrote:
"Edward Green" <spamspamspam3@netzero.com> wrote in message
news:1169423302.676710.160990@38g2000cwa.googlegroups.com...
<...>
Why in the name of Feynman would a kind of non-profit educationally
flavored organization choose this proprietary format to encode their
"four priceless archival recordings". I hate media players in general
as a species -- they all want to preempt all your formats and bombard
you with unwanted "content" when you download them. A pox on all their
houses.
Why .rm ? No idea, except that compression is not bad and it's possible they
hoped that it would be easier to keep them from being downloaded as files (I
know it can be done, but its not quite as simple as right click, Save Target
as. . .).
I think it used to be the case that the BBC website offered a specially
tailored version of Real Player that was less annoying than the standard
one. I can't guarantee that this will work for you (particularly if you live
outside UK), but you could start from here.
http://www.bbc.co.uk/webwise/categories/plug/real/newreal.shtml?newintro
Thanks... that worked. Although I think this was in fact the fully
annoying standard version (I had to go through and uncheck "No, thank
you, I would _not_ like you to play XXX files, or XXY files, or .... I
am quite happy with my current slick commercial product, and do not
wish to substitute your slick commercial product". Media players have
the ethics of personal injury lawyers.
How did we wind up with about 30 formats of "media" files?
Notwithstanding all that, the lectures are well worth viewing.
Yes! I just started, and I realized, I never have seen a film of
Feynman lecturing.
A minute or two quite demystified him for me. He's from Far Rockaway.
I'm from not too far away from Far Rockaway. As he spoke, I heard a
hobby shop owner/odd jobber I knew as a child lecturing about physics.
Looked about the same, and spoke very much the same. His was a very
characteristic New York voice and delivery.
Damndest thing... how a shop owner from Queens could be standing up
pretending to deliver a lecture in theoretical physics! Seemed to fool
'em all, too. ;-)
.
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| User: "dogma" |
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| Title: Re: Interaction of EM radiation with matter |
22 Jan 2007 01:18:16 AM |
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nomed,
try: hyperphysics.phy-astr.gsu.edu
Edward Green wrote:
OG wrote:
"Edward Green" <spamspamspam3@netzero.com> wrote in message
news:1169423302.676710.160990@38g2000cwa.googlegroups.com...
<...>
Why in the name of Feynman would a kind of non-profit educationally
flavored organization choose this proprietary format to encode their
"four priceless archival recordings". I hate media players in general
as a species -- they all want to preempt all your formats and bombard
you with unwanted "content" when you download them. A pox on all their
houses.
Why .rm ? No idea, except that compression is not bad and it's possible they
hoped that it would be easier to keep them from being downloaded as files (I
know it can be done, but its not quite as simple as right click, Save Target
as. . .).
I think it used to be the case that the BBC website offered a specially
tailored version of Real Player that was less annoying than the standard
one. I can't guarantee that this will work for you (particularly if you live
outside UK), but you could start from here.
http://www.bbc.co.uk/webwise/categories/plug/real/newreal.shtml?newintro
Thanks... that worked. Although I think this was in fact the fully
annoying standard version (I had to go through and uncheck "No, thank
you, I would _not_ like you to play XXX files, or XXY files, or .... I
am quite happy with my current slick commercial product, and do not
wish to substitute your slick commercial product". Media players have
the ethics of personal injury lawyers.
How did we wind up with about 30 formats of "media" files?
Notwithstanding all that, the lectures are well worth viewing.
Yes! I just started, and I realized, I never have seen a film of
Feynman lecturing.
A minute or two quite demystified him for me. He's from Far Rockaway.
I'm from not too far away from Far Rockaway. As he spoke, I heard a
hobby shop owner/odd jobber I knew as a child lecturing about physics.
Looked about the same, and spoke very much the same. His was a very
characteristic New York voice and delivery.
Damndest thing... how a shop owner from Queens could be standing up
pretending to deliver a lecture in theoretical physics! Seemed to fool
'em all, too. ;-)
.
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| User: "MathMagician" |
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| Title: Re: Interaction of EM radiation with matter |
21 Jan 2007 11:26:49 AM |
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"Nomed" <querygroup@gmail.com> wrote in message =
news:1169396532.724841.319790@m58g2000cwm.googlegroups.com...
I would like to know how EM radiation (in the vicinity of the visible
spectrum) interacts with matter to give us the phenomena of =
reflection,
refraction, etc ...
=20
I want to understand this at the most fundamental level, and not in =
the
high level abstraction of classical optics.
You want to know rather a lot in one go, don't you?
=20
=20
For example, when photons of light "strike" a reflective surface do
they simply "bounce" off the atoms (as I've been told!), or are they
absorbed and re-emitted? How long does this process take?
=20
They "bounce".=20
If absorbed they re-emit at a later time and in a different (random)
direction. A photon is a packet of energy, it can be (and often is)
divided into smaller packets. When you see white hot metal cooling
to red it is emitting ever lower frequency photons, and can feel
the heat on your skin long after it has cooled past the red stage.
Check in the kitchen, dont burn yourself on the oven.
Assuming the later is correct, how is light incident at X degrees
reflected at 180-X degrees, i.e., how are the photons re-emitted at
180-X degrees?
The latter is not correct.
Just remember that water going over Niagara Falls has more energy
than an industrial water jet, but the latter can cut carpet (or your=20
finger off). One photon from a heater has a lot less energy than
one photon from a light bulb, but there are more of them.
=20
Is all non-direct light (i.e., reflected light)
ultimately re-emitted photons from light-matter interactions? Is this
light re-emitted at the same frequencies as the incident photons?
=20
I'd imagine quantum mechanics equations are required to answer these
questions, so a pointer to a suitable web resource would be useful.
I've tried in vain to find such a source.
=20
Thanks.
.
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| User: "Nomed" |
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| Title: Re: Interaction of EM radiation with matter |
21 Jan 2007 12:41:51 PM |
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So how do photons "bounce" off matter? Do they hit the atoms?
And how does a "red" object selectively absorb photons outside the
"red" region of the spectrum while the "red" photons simply "bounce"
off?
MathMagician wrote:
"Nomed" <querygroup@gmail.com> wrote in message news:1169396532.724841.319790@m58g2000cwm.googlegroups.com...
I would like to know how EM radiation (in the vicinity of the visible
spectrum) interacts with matter to give us the phenomena of reflection,
refraction, etc ...
I want to understand this at the most fundamental level, and not in the
high level abstraction of classical optics.
You want to know rather a lot in one go, don't you?
For example, when photons of light "strike" a reflective surface do
they simply "bounce" off the atoms (as I've been told!), or are they
absorbed and re-emitted? How long does this process take?
They "bounce".
If absorbed they re-emit at a later time and in a different (random)
direction. A photon is a packet of energy, it can be (and often is)
divided into smaller packets. When you see white hot metal cooling
to red it is emitting ever lower frequency photons, and can feel
the heat on your skin long after it has cooled past the red stage.
Check in the kitchen, dont burn yourself on the oven.
Assuming the later is correct, how is light incident at X degrees
reflected at 180-X degrees, i.e., how are the photons re-emitted at
180-X degrees?
The latter is not correct.
Just remember that water going over Niagara Falls has more energy
than an industrial water jet, but the latter can cut carpet (or your
finger off). One photon from a heater has a lot less energy than
one photon from a light bulb, but there are more of them.
Is all non-direct light (i.e., reflected light)
ultimately re-emitted photons from light-matter interactions? Is this
light re-emitted at the same frequencies as the incident photons?
I'd imagine quantum mechanics equations are required to answer these
questions, so a pointer to a suitable web resource would be useful.
I've tried in vain to find such a source.
Thanks.
.
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| User: "MathMagician" |
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| Title: Re: Interaction of EM radiation with matter |
21 Jan 2007 01:47:34 PM |
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"Nomed" <querygroup@gmail.com> wrote in message =
news:1169404911.453569.117320@m58g2000cwm.googlegroups.com...
So how do photons "bounce" off matter? Do they hit the atoms?
That's where you need high level abstraction of classical optics...
Perhaps the easiest way to understand reflection is to treat a photon
like a basketball bouncing off the hoop, if you get the shot right=20
the ball goes in.
http://tinyurl.com/2v56u6
You can't tell which way it will bounce, but you can have some=20
confidence when you bounce it on the plane of the floor.
Balls bigger than the holes bounce, golf balls go right through.=20
A ball that is the exact size will stick in the hoop and be "absorbed".
X-rays are like golf balls. The danger is that if they ARE absorbed
in the genes in your body cells, that can mutate the cell, causing
the cell to malfunction and that can lead to cancer. For that=20
reason it isn't wise to have too many x-rays.
And how does a "red" object selectively absorb photons outside the
"red" region of the spectrum while the "red" photons simply "bounce"
off?
It's actually the other way around. A surface which absorbs=20
everything except red (which it reflects) is called a red surface.
Leaves and grass are green to absorb sunlight. White clouds
reflect.
"How" is a matter of resonance. Different antennae operate
at different frequencies, your cell phone doesn't have a dish
pointed at a satellite. The rods and cones of your retina are
tiny antennae which absorb just those frequencies we call
call "visible", reflecting others. Most solar radiation is=20
reflected and our eyes have evolved to operate only in the=20
limited range of frequencies that get through atmosphere.
Bees (and other insects) can see in the ultraviolet, they have
smaller eyes. Cat's eyes are a common example of light
being reflected by the retina.=20
=20
MathMagician wrote:
"Nomed" <querygroup@gmail.com> wrote in message =
news:1169396532.724841.319790@m58g2000cwm.googlegroups.com...
I would like to know how EM radiation (in the vicinity of the =
visible
spectrum) interacts with matter to give us the phenomena of =
reflection,
refraction, etc ...
I want to understand this at the most fundamental level, and not in =
the
high level abstraction of classical optics.
You want to know rather a lot in one go, don't you?
For example, when photons of light "strike" a reflective surface do
they simply "bounce" off the atoms (as I've been told!), or are =
they
absorbed and re-emitted? How long does this process take?
They "bounce".
If absorbed they re-emit at a later time and in a different (random)
direction. A photon is a packet of energy, it can be (and often is)
divided into smaller packets. When you see white hot metal cooling
to red it is emitting ever lower frequency photons, and can feel
the heat on your skin long after it has cooled past the red stage.
Check in the kitchen, dont burn yourself on the oven.
Assuming the later is correct, how is light incident at X degrees
reflected at 180-X degrees, i.e., how are the photons re-emitted at
180-X degrees?
The latter is not correct.
Just remember that water going over Niagara Falls has more energy
than an industrial water jet, but the latter can cut carpet (or your
finger off). One photon from a heater has a lot less energy than
one photon from a light bulb, but there are more of them.
Is all non-direct light (i.e., reflected light)
ultimately re-emitted photons from light-matter interactions? Is =
this
light re-emitted at the same frequencies as the incident photons?
I'd imagine quantum mechanics equations are required to answer =
these
questions, so a pointer to a suitable web resource would be useful.
I've tried in vain to find such a source.
=20
Thanks.
.
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| User: "Sam Wormley" |
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| Title: Re: Interaction of EM radiation with matter |
21 Jan 2007 01:02:03 PM |
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Nomed wrote:
So how do photons "bounce" off matter? Do they hit the atoms?
And how does a "red" object selectively absorb photons outside the
"red" region of the spectrum while the "red" photons simply "bounce"
off?
Photon's do three things
o comes into existence being emitted by a charged particle for
one reason or another... and not deterministically.
o propagates along a geodesic
o is absorbed by a charged particle
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| User: "Martin Hogbin" |
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| Title: Re: Interaction of EM radiation with matter |
21 Jan 2007 03:53:55 PM |
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"Nomed" <querygroup@gmail.com> wrote in message news:1169396532.724841.319790@m58g2000cwm.googlegroups.com...
I would like to know how EM radiation (in the vicinity of the visible
spectrum) interacts with matter to give us the phenomena of reflection,
refraction, etc ...
I want to understand this at the most fundamental level, and not in the
high level abstraction of classical optics.
For example, when photons of light "strike" a reflective surface do
they simply "bounce" off the atoms (as I've been told!), or are they
absorbed and re-emitted? How long does this process take?
Assuming the later is correct, how is light incident at X degrees
reflected at 180-X degrees, i.e., how are the photons re-emitted at
180-X degrees? Is all non-direct light (i.e., reflected light)
ultimately re-emitted photons from light-matter interactions? Is this
light re-emitted at the same frequencies as the incident photons?
I'd imagine quantum mechanics equations are required to answer these
questions, so a pointer to a suitable web resource would be useful.
I've tried in vain to find such a source.
Try this book:
QED - The strange theory of light and matter
by Richard P Feynman
Penguin science paperback
ISBN 0-14-012505-1
Martin Hogbin
.
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| User: "Sam Wormley" |
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| Title: Re: Interaction of EM radiation with matter |
21 Jan 2007 01:00:05 PM |
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Nomed wrote:
I would like to know how EM radiation (in the vicinity of the visible
spectrum) interacts with matter to give us the phenomena of reflection,
refraction, etc ...
I want to understand this at the most fundamental level, and not in the
high level abstraction of classical optics.
Read Feynman's book, "QED: The strange theory of light and matter".
.
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