electric and magnetic field vectors of photon Text

alistair

Jul15-04, 04:57 AM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no,location=no,scrollbars=yes,resizable=yes,status=no,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\nWhy is the magnetic field of a photon so weak compared to its electric field,\nwhen the magnetic field carries as much energy as the electric field?\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>Why is the magnetic field of a photon so weak compared to its electric field,
when the magnetic field carries as much energy as the electric field?

John T Lowry

Jul15-04, 03:23 PM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no,location=no,scrollbars=yes,resizable=yes,status=no,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n"alistair" <alistair@goforit64.fsnet.co.uk> wrote in message\nnews:861c1b21.0407141352.a8d4330@posting.google.com...\n>\n>\n> Why is the magnetic field of a photon so weak compared to its electric\nfield,\n> when the magnetic field carries as much energy as the electric field?\n\nThere much more to this than meets the eye. First of all, if you have a\nstate with a definite number of photons of known type, the average\nvalues of the electric and magnetic field vectors are zero. You won\'t\nhave much luck trying to think of a photon as some sort of\nelectromagnetic field burst or wave packet. Sorry.\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>"alistair" <alistair@goforit64.fsnet.co.uk> wrote in message
news:861c1b21.0407141352.a8d4330@posting.google.com...
>
>
> Why is the magnetic field of a photon so weak compared to its electric
field,
> when the magnetic field carries as much energy as the electric field?

There much more to this than meets the eye. First of all, if you have a
state with a definite number of photons of known type, the average
values of the electric and magnetic field vectors are zero. You won't
have much luck trying to think of a photon as some sort of
electromagnetic field burst or wave packet. Sorry.

p.kinsler@imperial.ac.uk

Jul16-04, 09:19 AM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no,location=no,scrollbars=yes,resizable=yes,status=no,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\n> "alistair" <alistair@goforit64.fsnet.co.uk> wrote in message\n> news:861c1b21.0407141352.a8d4330@posting.google.com...\n> > Why is the magnetic field of a photon so weak compared to its\n> > electric field, when the magnetic field carries as much energy\n> > as the electric field?\n\n"Weak compared" implies a comparison, but E and B fields have\ndifferent units, so comparison is tricky, short of going to\nsome dimensionless units which might be theoretically pleasing\nbut difficult to relate to real situations.\n\nDo you perhaps mean why are the effects of the mag field (B)\nof a photon much smaller than the effects of electric field\n(E)? That\'s easy -- in general, materials are much less\nmagnetic than they are "electric".\n\nHowever, John T Lowry <jlowry100@earthlink.net> replied:\n> There much more to this than meets the eye. First of all, if you have a\n> state with a definite number of photons of known type, the average\n> values of the electric and magnetic field vectors are zero. You won\'t\n> have much luck trying to think of a photon as some sort of\n> electromagnetic field burst or wave packet. Sorry.\n\nThat\'s might be true, but I don\'t see how it answers alistair\'s\nquestion. In any case, a photon with it\'s zero average E and B\nfield can still interact with an atom quite effectively via a\nelectric dipole interaction, but the same photon will rarely find\nan atom to have an equally strong magnetic dipole interaction\nwith (if yo\'ll forgive the handwaving language this once).\n\n--\n---------------------------------+---------------------------------\nDr. Paul Kinsler\nBlackett Laboratory (QOLS) (ph) +44-20-759-47520 (fax) 47714\nImperial College London, Dr.Paul.Kinsler@physics.org\nSW7 2BW, United Kingdom. http://www.qols.ph.ic.ac.uk/~kinsle/\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>"alistair" <alistair@goforit64.fsnet.co.uk> wrote in message
> news:861c1b21.0407141352.a8d4330@posting.google.com...
> > Why is the magnetic field of a photon so weak compared to its
> > electric field, when the magnetic field carries as much energy
> > as the electric field?

"Weak compared" implies a comparison, but E and B fields have
different units, so comparison is tricky, short of going to
some dimensionless units which might be theoretically pleasing
but difficult to relate to real situations.

Do you perhaps mean why are the effects of the mag field (B)
of a photon much smaller than the effects of electric field
(E)? That's easy -- in general, materials are much less
magnetic than they are "electric".

However, John T Lowry <jlowry100@earthlink.net> replied:
> There much more to this than meets the eye. First of all, if you have a
> state with a definite number of photons of known type, the average
> values of the electric and magnetic field vectors are zero. You won't
> have much luck trying to think of a photon as some sort of
> electromagnetic field burst or wave packet. Sorry.

That's might be true, but I don't see how it answers alistair's
question. In any case, a photon with it's zero average E and B
field can still interact with an atom quite effectively via a
electric dipole interaction, but the same photon will rarely find
an atom to have an equally strong magnetic dipole interaction
with (if yo'll forgive the handwaving language this once).

--
---------------------------------+---------------------------------
Dr. Paul Kinsler
Blackett Laboratory (QOLS) (ph) +44-20-759-47520 (fax) 47714
Imperial College London, Dr.Paul.Kinsler@physics.org
SW7 2BW, United Kingdom. http://www.qols.ph.ic.ac.uk/~kinsle/

ueb

Jul16-04, 09:20 AM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no,location=no,scrollbars=yes,resizable=yes,status=no,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\n\nalistair wrote:\n\n> Why is the magnetic field of a photon so weak compared to its electric field,\n> when the magnetic field carries as much energy as the electric field?\n\nHow do you call the magnetic field "weak compared to its electric field"?\nSee also\nhttp://groups.google.com/groups?selm=a4v9cc.s5.ln%40Muse2.private.de\nin which it is demonstrated that both electric & magnetic component\nof a photon respectively an electromagnetic wave are equal with\nregard to the "strength" or "weakness".\nBTW, the energy is "carried" by the entire field, not from a single\ncomponent.\n\nUlrich\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>alistair wrote:

> Why is the magnetic field of a photon so weak compared to its electric field,
> when the magnetic field carries as much energy as the electric field?

How do you call the magnetic field "weak compared to its electric field"?
See also
http://groups.google.com/groups?selm=a4v9cc.s5.ln%40Muse2.private.de
in which it is demonstrated that both electric & magnetic component
of a photon respectively an electromagnetic wave are equal with
regard to the "strength" or "weakness".
BTW, the energy is "carried" by the entire field, not from a single
component.

Ulrich

FrediFizzx

Jul19-04, 04:09 AM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no,location=no,scrollbars=yes,resizable=yes,status=no,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\n<p.kinsler@imperial.ac.uk> wrote in message\nnews:j1kks1-gai.ln1@delillo.lsr.ph.ic.ac.uk...\n|\n|\n| > "alistair" <alistair@goforit64.fsnet.co.uk> wrote in message\n| > news:861c1b21.0407141352.a8d4330@posting.google.com...\n| > > Why is the magnetic field of a photon so weak compared to its\n| > > electric field, when the magnetic field carries as much energy\n| > > as the electric field?\n|\n| "Weak compared" implies a comparison, but E and B fields have\n| different units, so comparison is tricky, short of going to\n| some dimensionless units which might be theoretically pleasing\n| but difficult to relate to real situations.\n\nHmmm... In gaussian cgs units, E and B fields have the same units;\nsqrt(energy/volume).\n\n| Do you perhaps mean why are the effects of the mag field (B)\n| of a photon much smaller than the effects of electric field\n| (E)? That\'s easy -- in general, materials are much less\n| magnetic than they are "electric".\n\nThis is probably a more likely scenario. Plus the magnetic force does no\nwork. I do believe the magnetic and electric energies of a free space\nphoton would be equal during any interval of time much shorter than its\nwavelength. If it were possible to measure that.\n\nFrediFizzx\n\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky><p.kinsler@imperial.ac.uk> wrote in message
news:j1kks1-gai.ln1@delillo.lsr.ph.ic.ac.uk...
|
|
| > "alistair" <alistair@goforit64.fsnet.co.uk> wrote in message
| > news:861c1b21.0407141352.a8d4330@posting.google.com...
| > > Why is the magnetic field of a photon so weak compared to its
| > > electric field, when the magnetic field carries as much energy
| > > as the electric field?
|
| "Weak compared" implies a comparison, but E and B fields have
| different units, so comparison is tricky, short of going to
| some dimensionless units which might be theoretically pleasing
| but difficult to relate to real situations.

Hmmm... In gaussian cgs units, E and B fields have the same units;
\sqrt(energy/volume).

| Do you perhaps mean why are the effects of the mag field (B)
| of a photon much smaller than the effects of electric field
| (E)? That's easy -- in general, materials are much less
| magnetic than they are "electric".

This is probably a more likely scenario. Plus the magnetic force does no
work. I do believe the magnetic and electric energies of a free space
photon would be equal during any interval of time much shorter than its
wavelength. If it were possible to measure that.

FrediFizzx