Partly a thought experiment, partly inspired by the "Line to the Moon" thread...

 

Imagine if you will that YT is building a lamp in his work room. He has a battery terminal connected to a bulb with a short piece of wire. He connects his last piece of wire to the other terminal but is shocked to find that this piece is millions of miles long.

 

YT decides to be fancy and launches the end of the wire into space with one of his home made rockets, then recovers it a year later (pretend this is at all possible). The larger piece of wire should now be assumed to occupy the same solar orbital in which Earth travels.

 

The question is, when YT connects this end of the wire to the light bulb, will the circuit be completed (and hence the bulb illuminated) instantaneously?

 

Give reasoning and neglect the heat effects of solar radiation.

Ignoring resistance. Well dissipation due to it.

 

Nope, there is a fixed velocity (the speed of light in the material) for the propagation of the field within the wire.

I am going to add SUMS to this to make it more FUN for the bored ones.

 

If you say "no - not instantaneous", then calculate time difference between connection of circuit and illumination of bulb.

 

With and without resistance (assume copper wire of 1.4mm diameter).

 

i would have to disagree with you klaynos. the voltage provided by the battery would already be producing a local current. unless the current magically doesn't start till the voltage jump goes round the entire wire. that would mean that the battery could be disconnected and the bulb would stay lit wouldn't it?

 

sayonara, if you include resistance then you must explain how he got a hold of a 3TV battery.

 

oh wait, its YT isn't it. silly me, all is explained.

sayonara, if you include resistance then you must explain how he got a hold of a 3TV battery.

 

oh wait, its YT isn't it. silly me, all is explained.

 

lol

 

You raise a good point though, indirectly. People trying to solve for this might want to declare some values (like, assume average radius of Earth's orbit, select arbitrary voltage, etc).

Well ignore IA, because I'm too tired to think it through properly.

 

Useing the information that I and other contributed in:

 

http://www.scienceforums.net/forum/showthread.php?t=25456&highlight=copper

 

swansont's post #7, the given velocity of electric field in copper is:

 

225,000 km/s

 

From wp (http://en.wikipedia.org/wiki/Earth), the orbital circumference is:

 

924,375,700 km

 

which gives us:

 

1.1 ish hours.

He connects his last piece of wire to the other terminal but is shocked to find that this piece is millions of miles long.

If one end of the long wire is already connected, the potential will arrive at the other end after 1.1hr like Klaynos calculated. During all the years it took to streatch the wire on earth orbit the potential was there so when he connect the wire, the bulb will be illuminated instantaneously.

If one end of the long wire is already connected, the potential will arrive at the other end after 1.1hr like Klaynos calculated. During all the years it took to streatch the wire on earth orbit the potential was there so when he connect the wire, the bulb will be illuminated instantaneously.

 

That's the bit I couldn't be bothered to think through properly

actually Propagation delays and standing waves are exploited all the time in RF circuitry.

 

oddly enough, if I disconnected the other end once set up, it would also take that length of time for the bulb to extinguish, therein lies the basic principal behind fullwave, halfwave etc... antennas.

 

the only difference is I would connect it in reverse polarity next time

That's the bit I couldn't be bothered to think through properly

 

Did we ever decide on this?

From the point where the power supply is attached it will take 1.1h for the potential to propagate down the wire, after this point as soon as you connect the circuit into a loop current will flow.

So if YT connected both ends at the same time, it would take 1.1 hours, but as the question is phrased, it would be instantaneous.

So if YT connected both ends at the same time, it would take 1.1 hours, but as the question is phrased, it would be instantaneous.

 

Yep

Totally

You probably would not even need the battery. If the loop was "cutting" magnetic flux lines, you would get a potential difference. At that size loop, probably a pretty damn big one, too.

Looks like you might need to rethink that design YT

 

*bang*

Current decays as it travels through a wire. The voltage needed at the start in order to get even a fraction of a volt at the end of a journey of this distance, would melt the equipment and probably a good bit of the surroundings. It just is not a practical thought experiment.

elas

Current decays as it travels through a wire. The voltage needed at the start in order to get even a fraction of a volt at the end of a journey of this distance, would melt the equipment and probably a good bit of the surroundings. It just is not a practical thought experiment.

elas

 

I think we ignored resistive losses or put in some nice signal boosters along the transmission line.