Right, need help with another formula please.

[MFeely88]

Well, not so much the formula, but the resistivity.

The resistance of a 2.5mm2 copper conductor of length 8m and resistivity p = 1.72 x 10-8 Ωm is: a) 0.055 Ω B) 0.55 Ω c) 0.12 Ω d) 5.56 Ω

I know the formula is R = pL/A (well, I believe it is). I just don't know how to work it out so I get the right answer. The part that's stumping me most is how do I interpret the p = 1.72 x 10-8 Ωm?

The answer I get is 0.000000054. It's safe to say I'm doing something completely wrong, I just can't seem to find out what it is.

 

[Banjo]

Hi mate,

i worked it out to be 0.055

1.72 x 10-8 Ωm x 8 / 2.5 x 10-6

you use -6 as you are converting into metre's squared.

Hope this helps.

Stu

 

[MFeely88]

Hi mate,i worked it out to be 0.055

1.72 x 10-8 Ωm x 8 / 2.5 x 10-6

you use -6 as you are converting into metre's squared.

Hope this helps.

Stu

You wouldn't believe how much it helps, thanks a lot mate.

 

[Robin Spark]

Hi Mfeely88,

just to clarify to help you understand a bit more

1 metre2=1000mm*1000mm= 10000000mm2

or

1mm2 = 1*10(to the power of-6)Metre2=0.000001M2

Just be aware that in some books it also might say resistivity of copper is either

1. 17.5 ohms *10-9

or

1.75ohms * 10-8

However these are both the same its just the decimal point is in a different place so dont get caught out.