Question?

[Wardy35]

Question:- A conductor has a cross-sectional area of 20mm2, a length of 48m and made of material with a resistivity of 0.02 micro ohms per meter, what is its resistance?

Once i get loads of answers i will tell you why i asked it.

Regards
Mick Ward

 

[DurhamSparky]

im always wrong so will not answer

 

[Wardy35]

Wrong i am afraid.

Here are the answers to choose from:-

a) 48 Kilo ohms
b) 48 ohms
c) 0.48 ohms
d) 0.048 ohms

 

[stef]

With the information given that should be 0.96 microohm/m

Sh£$, that's wrong !!!

2nd edit: micro ohms to ohms? Doesn't make sense. Is that all of the info given?

 

[DurhamSparky]

48 ohms!!!

 

[stef]

right, if the resistance is 0.2 micro ohms per metre per mm2

 

[Wardy35]

The question and answer is exactly how i have it in front of me but in another book i have a similar question which is:-
Calculate the resistance of 100m of copper cable of 1.5mm squared csa if the restivity of copper is taken as 17.5x10minus9 ohms/m.

Using the formula R=pl divided by a = ohms

Therefore 17.5x10minus9ohms/m x 100 m divided by 1.5x10minus6 m/s giving 1.16 ohms

My confusion is where did the 10minus 6 come from with the csa 1.5?

Does this make sense?

 

[Wardy35]

How did you get 48 ohms DurhamSparky?

Mick

 

[stef]

48 Ohms for 48m that would be 1 Ohm per meter? a bit high IMO.

 

[stef]

The higher the cross section the lower the resistance. 0.02 micro ohms is a bit low that is 2 * 10^-8 Ohms !!!

So 48m * 0.02 micro ohms/m/mm^2 / 20mm^2 = 4.8 uOhm ???

 

[DurhamSparky]

How did you get 48 ohms DurhamSparky?

Mick

i guessed my little socks off!!!

my calcs came out at 41 ohms!!!

 

[Wardy35]

I dont have that answer as an option, i am beginning to think whoever wrote this question was bored.

Mick

 

[Wardy35]

No wonder my brain cells are being scrambled hellpppp

 

[stef]

Sorry wardy, the information given doesn't add up

 

[Wardy35]

Figures, the book i am working fromis the OLCI workbook which was written in 2006, i also have Trevor Linsley's Electrical Installation Work Level 2 written in 2008 and they are totally different.