Re: Doppler effect and relative speeds?

From: Tom Capizzi (etianshrdlu_at_verizon.net)
Date: 02/13/05 

Date: Sun, 13 Feb 2005 04:55:41 GMT

"JM Albuquerque" <jm.aREM.OVE@sapo.pt> wrote in message
news:377ookF57r5tmU1@individual.net...
>
> "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
>

If you read your own references, at the end of node39 the summation affirms
that the electric field of charges is indeed conservative, and associated
with
a scalar potential. The non-conservative part is generated by a time-varying
magnetic field which is associated with a vector potential.

> 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

Your use of conservative here is only valid as a description. It is not the
field theory meaning of the term.

> 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.

So, you have written Ohm's Law. This does not imply that electric fields are
non-conservative.

> 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 this is inappropriate use of the term, and it generalizes a property
of one
specific kind of magnetic field to all possible shapes of magnetic fields.

> 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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