Resistivity

[manda]

Hi all.
I'm sorry if this is the wrong place to post this but I'm unsure where.
Could someone please break down this formula into easy to grasp terms for me.
R=Pl (ohms) divided by A
where P is the resistivity constant for the material (ohms m)
l=length of material (m)
a= cross sectional area of material (m2)

I have been given the resistivity of silver as 16.4 x 10-9 ohms meter.

Firstly: how is a cross sectional area different from an area?
secondly: does 16.4 X10-9 ohms mean i must multiply 16.4 x 10 minus nine and if not could someone please explain it?
this is just an example i have been given and would appreciate any help to understand it.
thanks all.

 

[Guest123]

An informative link here, with an actual calculator at the bottom too.

Resistance and Resistivity

 

[manda]

Thanks Lenny!

 

[JUD]

Hi all.
I'm sorry if this is the wrong place to post this but I'm unsure where.
Could someone please break down this formula into easy to grasp terms for me.
R=Pl (ohms) divided by A
where P is the resistivity constant for the material (ohms m)
l=length of material (m)
a= cross sectional area of material (m2)

I have been given the resistivity of silver as 16.4 x 10-9 ohms meter.

Firstly: how is a cross sectional area different from an area?
The cross sectional area is just that, the 2-dimensional area of a cross section (or slice) of an object.

secondly: does 16.4 X10-9 ohms mean i must multiply 16.4 x 10 minus nine and if not could someone please explain it?
It's actually 16.4 x 10 to the power of -9 or
16.4 x (10 divided by itself 9 times) or
16.4 x (10/10/10/10/10/10/10/10/10/10) or
16.4 x 0.000000001 = 0.0000000164

this is just an example i have been given and would appreciate any help to understand it.
thanks all.

My GREEN

 

[manda]

Thanks alot Jud! Think i've got it now.

 

[pushrod]

You need a scientific calculator for the 2330 something like THIS from casio about £8 in shops like wilkinsons. The button in the middle at the bottom will make dealing with all the 10 to the power x, or -x, questions dead easy.

 

[manda]

Thanks Pushrod. I have one but still figuring out what everything does.

 

[pushrod]

Just seen one of your previous posts about the BRB (17th wiring regs book) worth keeping an eye on ebay particularly if there are any lunchtime finishing auctions - i got a brand new copy for £37. You will also need an OSG (On Site Guide) if you haven't already got one.
This might go at a good price (RRP is about £20ish) new IEE Guide IEE Wiring Regulations 17th Edition on eBay (end time 21-Sep-10 20:59:43 BST) but you can get them on Amazon for about £16
HERE

 

[manda]

Thank you Pushrod, luckily the wiring regs book is supplied when needed in the course and will check now about the one you recommended. I think i need to find a separate course to learn how to use this damned calculator will take some getting used to me thinks.

 

[pushrod]

re - the calculator definitely worth going thru the instruction manual, if you didn't instantly bin it, to get used to it. If it is the casio one the x-1 button near the top right hand corner can certainly make resistances in parallel calculations massively quicker and easier. Good luck anyway.

 

[manda]

Yep that's the one. I did keep the manual and will read through it although I don't hold out much hope of it making much sense to me lol. Thanks for all the advice it's much appreciated!!