SR and a lightbulb [Relativity]

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From: dlzc on 31 Dec 2009 15:40

Dear Inertial:

On Dec 30, 5:14 pm, "Inertial" <relativ...(a)rest.com> wrote:
> "dlzc" <dl...(a)cox.net> wrote in message
....
> > Current flows are on the order of 0.1c,
> > and inductance of wiring will delay
> > onset of current flow by a good bit.
>
> The speed propagation of the EM in a
> good conductor (which we would assume
> we're dealing with) are around 60% to
> 95% of c.

This is current flow to light a light, presumably DC (or "50-60 Hz").
Small changes in such current flow in unshielded conductors (such as
he describes) propagate at 0.1c, give or take. You are thinking
higher frequency, and shielded cables or waveguides. Where you are
not "squeezing" the entire volume of the conductor to accept and yield
up conductance electrons.

> If you're talking about the speed of
> the random electrons movement in the
> conductor, that's a good deal less ..
> I think 0.1c is prob around the right
> magnitude .. and if no current is
> flowing, the net motion balances out.
>
> If you're talking about the electron
> drift speed (the net effect of overall
> motion of electrons in a conductor when
> current is applied) then that is VERY
> slow. A tortoise could beat electron
> drift and have time for a nap
> :):)

Agreed.

David A. Smith

From: PD on 6 Jan 2010 14:56

On Dec 29 2009, 8:39 pm, dk <dakalami...(a)sci.ccny.cuny.edu> wrote:
> Hi to all,
>
> Consider the following scenario:
>
> In frame S thare are two points, x1 and x2, a distance L apart. There
> are wires running from these two points such that x1 and x2 are
> connected to the '+' and '-' terminals of a battery in S. Now,
> image a lightbulb device with straight segments of wire extending from
> each of its terminals. The lightbulb device, in frame S', is moving
> with velocity v parallel and very close to the x axis of frame S. An
> observer in S notices that the lightbulb momentarily flashes as it
> passes by the x1-x2 region. This S observer correctly concludes that
> the length of the wire segments of the lightbulb device added up to
> exactly length L, since the lightbulb flashed, implying that the
> endpoints of those wires simultaneously coincided with x1 and x2,
> respectively, in S---Otherwise the circuit would not be complete and
> the lightbulb would not flash. However, since the observer in S will
> measure a length L for the lightbulb device, an observer at rest in S'
> will have to measure a proper length L' that is greater than L.
> Therefore, in frame S', the endpoints of the lightbulb device never
> coincide with x1 and x2 and the circuit never completes. How does the
> observer in S' explain the objective fact of the lightbulb flashing?
>
> thanks to all who might respond
> dk

The mistake is thinking that the *instant* both leads are in contact
with the rest of the circuit, the light bulb lights up. This
assumption violates the laws of physics.

I think you'll find that in order for the leads to be in contact for
enough time for a signal to propagate from one lead through the bulb
to the other lead, this extra length is more than enough to account
for why the bulb still lights up in the other frame where that bridge
part of the circuit is length-contracted.

This is very similar to the barn-and-pole puzzle where only one door
is left open, and the question is why doesn't the open barn door hit
the back of the pole?

"Henry Wilson" is desperate to believe that this thought experiment
"proves" that the light bulb lights in one frame and not in another,
but that is not the case.

From: Inertial on 7 Jan 2010 03:14

From: Androcles on 7 Jan 2010 03:33

"Henry Wilson DSc" <..@..> wrote in message
news:1t3bk51tof4e1crvaj5hsd533e61e3aee2(a)4ax.com...
> On Thu, 7 Jan 2010 15:12:24 +1100, "Inertial" <relatively(a)rest.com> wrote:
>
>>
>>"Henry Wilson DSc" <..@..> wrote in message
>>news:odmak592671hf2i6lr0tgcufhcoiqvh12o(a)4ax.com...
>>> On Wed, 6 Jan 2010 17:07:16 -0800 (PST), GA
>>> <gehan.ameresekere(a)gmail.com>
>>> wrote:
>
>>>>I ask if members of this group not know if a light bulb is switched
>>>>on or not.
>>>>
>>>>Here is a light bulb (-)
>>>>
>>>>Here is a light bulb switched on (O)
>>>>
>>>>
>>>>Observer the two persons at A and B viewing the bulb. The image of the
>>>>unlighted bulb impresses the retinas of the persons A and B for before
>>>>it is switched on.
>>>>
>>>>(-)(-)(-)(-)(-)(-)(-)(-)(-)(-)(-)(-)(-)(-)(-)(-)(-)
>>>> A B
>>>>
>>>>What A sees (-)
>>>>
>>>>What B sees (-)
>>>>
>>>>The bulb is switched on (O). A snapshot of the situation at time t is
>>>>shown below
>>>>
>>>>(O)(O)(O)(O)(O)(O)(O)(O)(-)(-)(-)(-)(-)(-)(-)(-)(-)
>>>>
>>>> A B
>>>
>>> No.
>>>
>>> (-)(-)(-)(-)(-)(-)(-)(O)(-)(-)(-)(-)(-)(-)(-)(-)(-)
>>>
>>> the two only connect in the frame that moves at v/2
>>
>>The wires connect in every frame .. but just not simultaneously in most.
>
> that's another way of saying current can only flow in one frame.
>
>>Whether or not some frame see the connection as simultaneous or not, the
>>same events happen regardless.
>
> Yes......and Einstein is wrong...Good...that's settled.
>
>>Either the connection is for long enough for
>>a current to be established and the light turns on .. or it isn't. The
>>frame of reference doesn't alter those events (only the relative timing of
>>some of them).
>
> you wouldn't make much of an electronic engineer.
>

For the light bulb to be on a current must flow.
For a current to flow the circuit must be complete.
The voltage travels from the switch to the bulb,
then the current commences.
The speed at which the voltage travels is a function
of the capacitance and inductance of the wire.
The analogy to this is turning on a tap. With the
tap off the pressure behind the tap is at its greatest
and reduces to zero as you measure back to the
reservoir. Opening the tap causes the water to
flow and the pressure behind the tap to fall to zero,
but water has inertia and doesn't flow instantly.
That means the pipe still has half pressure at half
height above the tap at the instant of turn on.
Whether you say the zero pressure travels back up
from the tap or the positive pressure travels down
to the tap is of no consequence, the flow is not
instantaneous due to the inertia of the mass of the
water.

"Inertial" would not make much of a plumber either.

Curiously, the sound from my (now very old) audio amplifier
continues on for four seconds and then fades after I switch the
power off. This is because the capacitors in the power supply
have to discharge.
http://www.uptownaudio.com/camb/camaudio540a.jpg

From: Inertial on 7 Jan 2010 17:33

"Henry Wilson DSc" <..@..> wrote in message
news:m8hck5paebibc012s1p1kn6dno7gsh6d57(a)4ax.com...
> On Thu, 7 Jan 2010 19:14:42 +1100, "Inertial" <relatively(a)rest.com> wrote:
>
>>
>>"Henry Wilson DSc" <..@..> wrote in message
>>news:1t3bk51tof4e1crvaj5hsd533e61e3aee2(a)4ax.com...
>>> On Thu, 7 Jan 2010 15:12:24 +1100, "Inertial" <relatively(a)rest.com>
>>> wrote:
>>>
>>>>
>>>>"Henry Wilson DSc" <..@..> wrote in message
>>>>news:odmak592671hf2i6lr0tgcufhcoiqvh12o(a)4ax.com...
>>>>> On Wed, 6 Jan 2010 17:07:16 -0800 (PST), GA
>>>>> <gehan.ameresekere(a)gmail.com>
>>>>> wrote:
>>>
>>>>>>I ask if members of this group not know if a light bulb is switched
>>>>>>on or not.
>>>>>>
>>>>>>Here is a light bulb (-)
>>>>>>
>>>>>>Here is a light bulb switched on (O)
>>>>>>
>>>>>>
>>>>>>Observer the two persons at A and B viewing the bulb. The image of the
>>>>>>unlighted bulb impresses the retinas of the persons A and B for before
>>>>>>it is switched on.
>>>>>>
>>>>>>(-)(-)(-)(-)(-)(-)(-)(-)(-)(-)(-)(-)(-)(-)(-)(-)(-)
>>>>>> A B
>>>>>>
>>>>>>What A sees (-)
>>>>>>
>>>>>>What B sees (-)
>>>>>>
>>>>>>The bulb is switched on (O). A snapshot of the situation at time t is
>>>>>>shown below
>>>>>>
>>>>>>(O)(O)(O)(O)(O)(O)(O)(O)(-)(-)(-)(-)(-)(-)(-)(-)(-)
>>>>>>
>>>>>> A B
>>>>>
>>>>> No.
>>>>>
>>>>> (-)(-)(-)(-)(-)(-)(-)(O)(-)(-)(-)(-)(-)(-)(-)(-)(-)
>>>>>
>>>>> the two only connect in the frame that moves at v/2
>>>>
>>>>The wires connect in every frame .. but just not simultaneously in most.
>>>
>>> that's another way of saying current can only flow in one frame.
>>
>>Nope. if it flows in one, it flows in all
>
> Precisely....which again proves Einstein to be an idiot.

No it does not .. as SR does not claim what you say it claims. You are
simply a liar.

>>>>Whether or not some frame see the connection as simultaneous or not, the
>>>>same events happen regardless.
>>>
>>> Yes......and Einstein is wrong...Good...that's settled.
>>
>>Why .. Einstein didn't say otherwise ... YOU did
>>
>>>>Either the connection is for long enough for
>>>>a current to be established and the light turns on .. or it isn't. The
>>>>frame of reference doesn't alter those events (only the relative timing
>>>>of
>>>>some of them).
>>>
>>> you wouldn't make much of an electronic engineer.
>>
>>Far better than you. You think someone walking past a light will make it
>>go
>>off, but still be on at the same time. Really, that's just nonsense. And
>>the only one claiming it is true is you. SR doesn't say that at all.
>
> SR can say anything in its version of fairyland.

Only in your uninformed little excuse for a brain.

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