HELP!!!! *physics*

[mistral4543]

Kaz - Sorry that I can't help much... the only thing I noticed is that unit length in the numerator and denominator of the first formula (R = rho * l/A) is inconsistent. Ie, the area should be converted into square metres since you've changed the length from km to m.

Gee, sorry I'm not much help... let's hope Mirac returns soon to help you out with this.

[Kaz]

Originally posted by mistral4543: Kaz - Sorry that I can't help much... the only thing I noticed is that unit length in the numerator and denominator of the first formula (R = rho * l/A) is inconsistent. Ie, the area should be converted into square metres since you've changed the length from km to m. Gee, sorry I'm not much help... let's hope Mirac returns soon to help you out with this.

I did, I just skipped that step. What I noticed was that I'm not exactly sure what unit rho is measured in...

[Avatar]

Kaz:

I'm doing Electronic Engineering at Cambridge 1st year:

R changes ONLY with material, temperature, length and area.

I think I ought to know...

Voltage (potential difference) is adjustable and the current THROUGH the resistor changes acoordingly. THE REISITOR can heat up as a result of this...

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Originally posted by 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?

Whoohooo Physics
Don;t you have Chemestry Questions?
I love thise

oh wait the question right...
Well Kazzy Honey
It's quite easy
If you higher the voltage and the resistance stays the same
What happens?
The Amperage highers aswell (the current through the resistor as Avatar calles it)

Simple in'it
so basicly U/I=l/A (i'm sure that th area ain't A but have no idea what it IS)




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[Mirac Honorguard]

Originally posted by Avatar: Kaz: I'm doing Electronic Engineering at Cambridge 1st year: R changes ONLY with material, temperature, length and area. I think I ought to know... Voltage (potential difference) is adjustable and the current THROUGH the resistor changes acoordingly. THE REISITOR can heat up as a result of this...

Hello fellow Electronic Engineer (I supposed to do second year, but I delayed for a half year).
Anyways, Rikard, that is NOT right what you've said about U/I = l/A. Kaz, forget that, not right!!
About your problem with the calculations, I did the calculation as well, this is how it should be :

rho = 0.017
l = 100 km = 100.000 m
A = 0.8 cm2 = 0.008 dm2 = 0.00008 m2
R = rho * l/A
R = 0.017 * (100.000/0.00008) = 21250000 ohm

This is totally different from the formula U/I = R !!!!!

I'll give a an example, try to solve this one :

What is R (using R = rho * l/A ) when
A = 10 dm2
l = 30 m
rho = 0.5
R =????

Solve R

With the R you calculated here
you go on with this question (using U/I=R is equal (if rewritten) to R*I =U ) :

U = ?????
I = 5000 mA
R = what you calculated in the first question.

I'll check in later this day, if you still can't solve it email me.
Hope this helps

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[This message has been edited by Mirac Honorguard (edited 10-22-2001).]

[DragonMage]

Originally posted by Mirac Honorguard: Hello fellow Electronic Engineer (I supposed to do second year, but I delayed for a half year). Anyways, Rikard, that is NOT right what you've said about U/I = l/A. Kaz, forget that, not right!! About your problem with the calculations, I did the calculation as well, this is how it should be : rho = 0.017 l = 100 km = 100.000 m A = 0.8 cm2 = 0.008 dm2 = 0.00008 m2 R = rho * l/A R = 0.017 * (100.000/0.00008) = 21250000 ohm This is totally different from the formula U/I = R !!!!! I'll give a an example, try to solve this one : What is R (using R = rho * l/A ) when A = 10 dm2 l = 30 m rho = 0.5 R =???? Solve R With the R you calculated here you go on with this question (using U/I=R is equal (if rewritten) to R*I =U ) : U = ????? I = 5000 mA R = what you calculator in the first question. I'll check in later this day, if you still can't solve it email me. Hope this helps

O....M....G....Beam me back down, Scotty. There IS intelligent life down there! Haven't seen the likes of this in years! Still hurts my head!

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Hopeless Romantic *sigh*

[Avatar]

Originally posted by DragonMage: O....M....G....Beam me back down, Scotty. There IS intelligent life down there! Haven't seen the likes of this in years! Still hurts my head!

Well quoted from Scott Adams's Dilbert Principle.....


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• Body Guard of Lioness
  
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• Winner of EPSRC 2000 Science Website is @
  http://www.epsrc-sciencerace.net/schools2000/534121/
  
• My own Forgotten Realms Website is @
  http://www.forgottenrealms.main-page.com[/list]

[Harkoliar]

AAAAAAAARRRRRRGGGGGG... physics, must run.. and hide.. and... groan...

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Revived I Am to hunt this world... Banish ye evil or face my wrath...

[DragonMage]

Originally posted by Avatar: Well quoted from Scott Adams's Dilbert Principle.....

Well, I hope you didn't think I was implying that no one else posting here was intelligent. Mirac's post just brought back terrifying memories of Electrical Engineering classes an old b/f of mine was taking, gee, 15 years ago. I would help him with the homework sometimes. *ouch, my brain*

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Alureth...Dragon friend of Breanna, Mage and Advisor in the Court of Lady Lioness

Co-Owner/Operator of the Evil Petting Zoo and devout member of the HADB clan.
Commander of the Dragon Fleet, IW Peacekeeping Force
Sublime Sister of the Illuminati - may the Light shine forever!
Second Historian and Scribe of IW. Mother Hen of IW.
Mage extraordinair, Pin-Up Girl for the OLD-COOTS
Magey-Wagey: performer in the Nekked Dancing Trio of the ORT.

Hopeless Romantic *sigh*

[Kaz]

I think I can think again today - so if R(cable) = rho * l/A; then R = U/I would be the resistance of the ENTIRE circuit (or whatever it's called in English). Right?
Also got my other physics thing sorted out, with a little help from the teacher. Logical, actually.