This official sponsor may provide discounts for members

# rho value

Discuss rho value in the Electrical Forum area at ElectriciansForums.net

P

#### philaxgt500

Welcome to ElectriciansForums.net - The American Electrical Advice Forum

i'm in year 3 and i'm stuck on a year 1 question, is there any hope for me??
i was wondering if someone could jog my memory on this 301 question please.

question:

A copper conductor has a rho value of 17.5 x 10-9. calculate the resistance of the copper wire if it's length is 20 meters and it's CSA is 2.5mm2

cheers phil

This official sponsor may provide discounts for members
A

17.5 x 10-9 x 20 /2.5 x 10-6 = 140 x 10-3 ohms

Last edited by a moderator:
G

#### Guest123

Hi Phil.

Ok so resistance (R) = (Rho x l)/s where l = length and s = CSA.

Are you sure you've got your units right?? as the resistivity of copper is 1.72x10-8 and they usually give the diameter of the wire not the CSA. So you would also need to work out the CSA = pie x r squared

Or is this a hypothetical question??

Let me know.

Cheers

A

resistance r = pl / a (ohms) p (the greek letter rho) is the resistiivity value for the material l is the length and a is the cross sectional area got the book next to me lol

G

#### Guest123

its been 9 years since I was in college and I aint got no books by me either. The old grey cells aint what they were.

I think I was right thought just with different letters. R= Rho (P) x length (L) / CSA (S).

Where L = length and S = CSA. Your book says CSA = A though.

Makes the same sum, thought doesn't it????

P

#### philaxgt500

I don't remember any of this, Cheers for the help.
And now for your next question,
A conductor 600mm long carries a current of 300 milli amps and is at 90 degrees to a magnectic field with density or 1.5T. determine the force exerted on the conductor.

A

erm dunno lol

G

#### Guest123

erm dunno lol
Trust me.

I don't remember any of this, Cheers for the help.
And now for your next question,
A conductor 600mm long carries a current of 300 milli amps and is at 90 degrees to a magnectic field with density or 1.5T. determine the force exerted on the conductor.
F=BIL but as your current is at 90 degrees to the field then the formula is F = BIL cosine theta. As the angle is 90 degrees then cosine theta = 1.

Where B = flux density, I = current, and L = length.

So - 1.5 x 0.003 x 600 = 2.7N.

I think. It's been a while since I did this stuff and my swede is aching a bit now.

Last edited by a moderator:

#### Mr Mark Sparks

##### -
all that to put a plug on

J

#### johnnyb

Lenny, take it N= Newtons, eh still remember that bit, ofcourse thats if i am right mate.

G

#### Guest123

Lenny, take it N= Newtons, eh still remember that bit, ofcourse thats if i am right mate.
Spot on Sir.

It's been a while for me too. The old grey matter is taking a bit of a bashing but it still seems to be working though.

Last edited by a moderator:
P

#### philaxgt500

Thanks alot everyone. i should hopefully be able to do the next 50 questions, But if i do get stuck i know where to come unless of course you want me to scan the page and put it up so you all can have a go at the 52 questions??

G

#### Guest123

I'd have a go Phil.
I liked doing the science when I was in college.

This official sponsor may provide discounts for members

Reply to rho value in the Electrical Forum area at ElectriciansForums.net

This official sponsor may provide discounts for members