HELP!!!! *physics*

[Kaz]

I am writing a Physics test on Thursday, and am kind of stuck on this point.
We are doing (among others) high voltage cables and why we use them. Now, I have a question. The resistance of the cables would be Resistance = rho * length/area (R=rho * l/A), rho being the resistance factor of the material. Now, you also calculate the resistance by Resistance = Voltage/Amperage (R = U/I). However, of course, if you change the voltage the resistance of the cables would change, but that is impossible because they are a fixed length, area and material! HELP!!! What changes? What IS the resistance I got in the second computation?

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[Ronn_Bman]

Originally posted by Kaz: What IS the resistance I got in the second computation?

That would be the resistance of my thick skull, and your trying to run this question through it


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There is sobbing of the strong,
And a pall upon the land;
But the People in their weeping
Bare the iron hand:
Beware the People weeping
When they bare the iron hand.

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[Arvon]

It's been a few thousand years since I had to deal with this, but if you change voltage the current changes.

I wish you good luck since I can't help you.
I'm in the second class of high school you know!

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Where there are monsters and barbarians there will be Byronas fighting against them.

[Kaz]

I'm in 10th - when does High School start in Greece? I hope I didn't mess the whole thing up - I had to translate all the technical terms from German into English, I may have gotten some wrong.

A man starts high school in Greece after 6 years in primary school.

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Where there are monsters and barbarians there will be Byronas fighting against them.

[Neb]

Ack! Not physics! I'm allergic to that! Save meeeeee! I'm meeeeeeeeeltiiiiing!

[Kaz]

Originally posted by Neb: Ack! Not physics! I'm allergic to that! Save meeeeee! I'm meeeeeeeeeltiiiiing!

I DID say *physics* in the title, if you read it it's your own fault. *fetches bucket* Here, melt into that.

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Sapphire Dragoness of ALSB
Waitress at Cloudy's Cafe
Guardian of the Temple of Aerie (specialized in GenCon and BG)
Magess of Lady Lioness' Court
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Historian of IW
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Lux omnis est
Once Upon A Paper Writer's Forum

[Mirac Honorguard]

Originally posted by Arvon: It's been a few thousand years since I had to deal with this, but if you change voltage the current changes.

Yes, Kaz, what Avron says here is true, the resistance of the wires are always the same the U/I = R is just a way to calculate the value of the resistance if you don't have any other information. so shortly put, R (resistance) is always the same, if the voltage (U) changes it only affects the current (I) and if the current (I) changes, the voltage (U) is likely to change.
Hope this helps, if you have more physics questions, just shoot, I'm in this business


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[Kaz]

Hm... but if I have both U and I and they do not add up to the R I got by rho*length/Area? To be more exact, something like this

R = rho * l/A
R = U/I
rho = 0.017
l= 100km
A = 0.8 cm2
U = 150kV
I = 533.33 A
Therefore
R = rho * l/A
R = 0.017 Ohm per whatever * 100km/0.8cm
R = 212500 Ohm

HOWEVER
R = U/I
R = 150000V/533.33A
R = 281.25 Ohm

WHAT THE HECK? THE RESISTANCE CAN'T BE 212500 Ohm AND 281.25 Ohm AT THE SAME TIME!!!! *sob*



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Sapphire Dragoness of ALSB
Waitress at Cloudy's Cafe
Guardian of the Temple of Aerie (specialized in GenCon and BG)
Magess of Lady Lioness' Court
Saint of the SoS
Historian of IW
Most Illustrious Arch-Magess of the Illuminati
Lux omnis est
Once Upon A Paper Writer's Forum