SR and a lightbulb
in [Relativity]
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From: Cocoon on 30 Dec 2009 07:20 On Dec 30, 4:17 am, dlzc <dl...(a)cox.net> wrote: > On Dec 29, 7:46 pm, dk <dakalami...(a)sci.ccny.cuny.edu> wrote: > > > I should have mentioned that it is assumed > > that the wires on the lightbulb device are > > insulated and only at their endpoints is the > > conductor exposed so as to make contact with > > x1 and x2 in frame S. > > Draw a diagram. How are the wires oriented wrt the x axis? this is insignificant > > Next, wires have inductance. Only in a fantasy world does the light > "flash". this too, except that you are right about the fantasy world > > David A. Smith Good Bye
From: Cocoon on 30 Dec 2009 07:29 On Dec 30, 4:25 am, "Inertial" <relativ...(a)rest.com> wrote: > "dk" <dakalami...(a)sci.ccny.cuny.edu> wrote in message [snip imbecility] > No .. that would be nonsense. > > What happens is that the two set of wires do not connect at the same time in > S' and do not disconnect at the same time in S'. If the bulb is to light, > they would need to both stay connected long enough for a current to flow. so, you need thick connectors, this is what you say, right?
From: Inertial on 30 Dec 2009 08:37 "Cocoon" <wy45e7hs(a)hushmail.com> wrote in message news:4b8be11a-d45c-453e-84fb-b8dbd3eb6cbb(a)r5g2000yqb.googlegroups.com... > On Dec 30, 4:25 am, "Inertial" <relativ...(a)rest.com> wrote: >> "dk" <dakalami...(a)sci.ccny.cuny.edu> wrote in message > > [snip imbecility] > >> No .. that would be nonsense. >> >> What happens is that the two set of wires do not connect at the same time >> in >> S' and do not disconnect at the same time in S'. If the bulb is to >> light, >> they would need to both stay connected long enough for a current to flow. > > so, you need thick connectors, > this is what you say, right? Thick enough to make a contact long enough. That's if there is any chance for the bulb to flash. Of course, there's not enough info to know whether the bulb will flash. But probably not if the wires are passing so fast that the length contraction is noticeable. There would need to be a large surface area for them to remain in contact long enough as they slide past each other. My guess is that there is no flash in either frame at any relatively fast speed for the two frame to be move wrt each other.
From: Greg Neill on 30 Dec 2009 09:20 Inertial wrote: > "Cocoon" <wy45e7hs(a)hushmail.com> wrote in message > news:4b8be11a-d45c-453e-84fb-b8dbd3eb6cbb(a)r5g2000yqb.googlegroups.com... >> On Dec 30, 4:25 am, "Inertial" <relativ...(a)rest.com> wrote: >>> "dk" <dakalami...(a)sci.ccny.cuny.edu> wrote in message >> >> [snip imbecility] >> >>> No .. that would be nonsense. >>> >>> What happens is that the two set of wires do not connect at the same time >>> in >>> S' and do not disconnect at the same time in S'. If the bulb is to >>> light, >>> they would need to both stay connected long enough for a current to flow. >> >> so, you need thick connectors, >> this is what you say, right? > > Thick enough to make a contact long enough. That's if there is any chance > for the bulb to flash. > > Of course, there's not enough info to know whether the bulb will flash. But > probably not if the wires are passing so fast that the length contraction is > noticeable. There would need to be a large surface area for them to remain > in contact long enough as they slide past each other. > > My guess is that there is no flash in either frame at any relatively fast > speed for the two frame to be move wrt each other. The OP did not consider the fact that the speed of the electric field in a conductor is quite a bit less less than c. If the connection points are small and the light bulb wires moving at near c, there will be insufficient time for the field to traverse the wire to make the circuit and light the bulb in either frame.
From: Inertial on 30 Dec 2009 09:32
"Greg Neill" <gneillRE(a)MOVEsympatico.ca> wrote in message news:4b3b6199$0$29200$9a6e19ea(a)news.newshosting.com... > Inertial wrote: >> "Cocoon" <wy45e7hs(a)hushmail.com> wrote in message >> news:4b8be11a-d45c-453e-84fb-b8dbd3eb6cbb(a)r5g2000yqb.googlegroups.com... >>> On Dec 30, 4:25 am, "Inertial" <relativ...(a)rest.com> wrote: >>>> "dk" <dakalami...(a)sci.ccny.cuny.edu> wrote in message >>> >>> [snip imbecility] >>> >>>> No .. that would be nonsense. >>>> >>>> What happens is that the two set of wires do not connect at the same > time >>>> in >>>> S' and do not disconnect at the same time in S'. If the bulb is to >>>> light, >>>> they would need to both stay connected long enough for a current to > flow. >>> >>> so, you need thick connectors, >>> this is what you say, right? >> >> Thick enough to make a contact long enough. That's if there is any >> chance >> for the bulb to flash. >> >> Of course, there's not enough info to know whether the bulb will flash. > But >> probably not if the wires are passing so fast that the length contraction > is >> noticeable. There would need to be a large surface area for them to > remain >> in contact long enough as they slide past each other. >> >> My guess is that there is no flash in either frame at any relatively fast >> speed for the two frame to be move wrt each other. > > The OP did not consider the fact that the speed of the > electric field in a conductor is quite a bit less less > than c. It depends on the conductor, of course. I suppose around 75% the speed of light would be typical. Good conductors can get above 90%. > If the connection points are small and the light > bulb wires moving at near c, there will be insufficient > time for the field to traverse the wire to make the > circuit and light the bulb in either frame. Yeup. And, of course, whether or not it lights up is not frame dependent. Either it does, or it doesn't. |