Re: Doppler effect and relative speeds?
From: JM Albuquerque (jm.aREM.OVE_at_sapo.pt)
Date: 02/13/05
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Date: Sun, 13 Feb 2005 01:35:06 -0000
"Tom Capizzi" <etianshrdlu@verizon.net> escreveu na mensagem
news:22uPd.28133$f%5.25194@trndny03...
>
> "JM Albuquerque" <jm.aREM.OVE@sapo.pt> wrote in message
> news:373s60F57eof7U1@individual.net...
> >
> > "Tom Capizzi" <etianshrdlu@verizon.net> escreveu na mensagem
> > news:D8WOd.23075$s16.8401@trndny02...
> >>
> >> "JM Albuquerque" <jm.aREM.OVE@sapo.pt> wrote in message
> >> news:371mifF580b7lU1@individual.net...
> >
> > (snip)
> >
> >> >> > Light is composed of a non-conservative field (electric) plus a
> >> >> > conservative
> >> >> > field (magnetic) at right angle and both together could be
> >> >> > quantized.
> >> >>
> >> >> Isn't that backwards? The electric field is the negative gradient of
a
> >> >> scalar potential
> >> >> and magnetic fields are the curl of a vector potential. Line
integrals
> >> >> in an electric
> >> >> field are zero (Kirchoff's law) and line integrals in a magnetic
field
> >> >> aren't necessarily.
> >> >
> >> >
> >> > Why backwards?
> >> > It is a circular problem, electric plus magnetic, plus electric, plus
> >> > magnetic, etc. You chose where to start.
> >> > The scalar potential of light doesn't exist in reality.
> >> > Light cannot be stopped, enclosed in a "light battery", like an
> >> > electric
> >> > potential can.
> >> > Light goes at the speed of light until it stops in a target and gives
> >> > its energy.
> >> >
> >>
> >> Light may be electromagnetic radiation, but the electric field and
> >> magnetic field exist independently of whether any light is being
> >> generated.
> >
> > Right.
> > So one could think about the electromagnetic field without any light
> > being generated.
> >
> >> The scalar potential is associated with electricity
> >> (otherwise known as voltage). As far as I know there is no scalar
> >> potential for light.
> >
> > Right.
> > That was an objection I've made about you statement above:
> > "The electric field is the negative gradient of a scalar potential"
> >
>
> I don't get what you object to. What I wrote is the definition of the
> electric field. It is not my opinion. Look in any text book.
>
> >
> >> My objection was you calling the electric field
> >> non-conservative and the magnetic field conservative.
> >> As I write this I'm not even sure any more that the magnetic field
> >> isn't also conservative, but I am sure the electric field is.
> >
> > The fact is that electric field is non-conservative and the magnetic
field
> > is conservative.
>
> Wrong. Apparently you don't know the meaning of conservative field.
> In a conservative field, work done is path-independent, and is simply
> described by the difference in some scalar potential at the two endpoints.
> In the case of the electric field, that scalar is voltage, and work done
in
> an electric field by moving a charge depends only on the initial and final
> voltage.
Apparently you are wrong, the electric field is non-conservative:
http://farside.ph.utexas.edu/teaching/em1/lectures/node38.html
http://farside.ph.utexas.edu/teaching/em1/lectures/node39.html
There are no magnetic monopoles.
So you only have magnetic dipoles and you know that all that goes out the
North pole must come in the South pole. This is conservation, hence
the magnetic field is conservative.
The electric field is different. Between potential voltages you have a
resistance and a current flowing - V=RI, so that you can have more or less
resistance and more or less current flowing for the same voltage drop.
Energy can be transformed between electric and mechanical, light, chemical,
or else any other energy type. Electricity is current after all.
> > That's what Maxell's equation says. That's what we
> > experience everyday live when the electricity build arrives (electricity
> > can
> > be transformed into other energy type and magnetic field cannot).
>
> Again wrong. If magnetic fields behaved the way you claim, there would be
> no power transformers, and no motors or generators. Maxwell's equations
> specify that a time varying magnetic field produces an electric field.
Within power transformers the magnetic field is only a conveyor between the
electrical energy transformation. The magnetic field does the job with 100%
efficiency, hence is conservative.
Again with motors and generators the magnetic field is the conveyor between
mechanical energy and electrical energy. All the dissipative fields are in
the side of electrical and mechanical, none on the magnetic field.
It is said that the magnetic field does no-work. I don't agree but lots of
people (including Bilge) told me that very loud and clear. I've found this
is just a matter of words and definitions, some times confused, or its me
who make the confusions. I'm always focused on "how it works" and so being
I'm always in trouble with relativity.
> > Also you
> > could find that you cannot shield the magnetic field (like gravity).
> >
>
> Ever hear of a superconductor? Magnetic fields cannot penetrate them.
OK.
I must review my point about shielding the magnetic field.
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