Resistivity maths problem

[Daniel Owens]

Hey all im just a bit confused with the formula for resistivity, i understand it until the text book gives an example whereupon the csa of cable goes from being 1.5mmsq (which i take to be 1.5 x 10 to -3M sq) to 1.5 x 10 to -6M sq which would make a csa of 1.5micrometeres would it not?
Ive attached a pic so you can see what i mean

Thanks

D

 

[Wilko]

Hi Daniel and Welcome to the Forum
No pic yet - if there's trouble uploading it could be from the Forum anti spam software, try refreshing the page and then immediately uploading.
Well 1mm is 1 x 10^-3m.
So 1mm2 is 1 x 10^-3 times 1 x 10^-3 which is 1 x 10^-6m2. Hopefully I haven't made a slip

 

[Richard Burns]

Welcome along, to add to wilko's coverage I posted this plan a little while ago to cover area and powers it might assist a bit.

 

[The Ghost]

Deleted as I can not upload a picture. At least the chinese input has done something...screwed up my interaction with the forum. Oh well better just keep quiet and let the spammers have their way.

 

[Daniel Owens]

Ok i get it now appreciate the quick response

 

[Daniel Owens]

Actually sorry to be a pain but ive put that in my calculator and squaring 1x10 to -3 still yields 1 x10 to -9
Am i misunderstanding something?
When you square numbers youre multiplying them by themselves yes?

 

[Richard Burns]

It sounds like you are squaring the power value as a number on its own, the calculator has not finished creating the 1 x 10^-3. You need to complete the 1 x 10^-3 calculation or put it in brackets to get your 0.001 and then square that to get 0.000001 or 1 x 10^-6.
When multiplying numbers with the same base you can add the powers. i.e. in this case -3 + -3 = -6.

 

[static zap]

Our common sense expects multiply to make bigger !
(but when it's less than 1 ..ie a quarter - things shrink)
..unless you have half a finger !

 

[telectrix]

It sounds like you are squaring the power value as a number on its own, the calculator has not finished creating the 1 x 10^-3. You need to complete the 1 x 10^-3 calculation or put it in brackets to get your 0.001 and then square that to get 0.000001 or 1 x 10^-6.
When multiplying numbers with the same base you can add the powers. i.e. in this case -3 + -3 = -6.

need to re-read when sober. ..... just did.... still too many 000000,a and -----'s to connect with senile brain.

 

[Daniel Owens]

It sounds like you are squaring the power value as a number on its own, the calculator has not finished creating the 1 x 10^-3. You need to complete the 1 x 10^-3 calculation or put it in brackets to get your 0.001 and then square that to get 0.000001 or 1 x 10^-6.
When multiplying numbers with the same base you can add the powers. i.e. in this case -3 + -3 = -6.

Ok thats working now, thanks for your help

D

 

[Daniel Owens]

And to everyone else who posted a reply

D