# Homework Help: Resistance in a lump of copper

1. Apr 7, 2005

### T7

Hi,

Part of a question I am working on asks me to "calculate the resistance of 1cm^3 of copper in the form of a thin sheet 0.5mm thick (between the faces of the sheet), given a resistivity of 1.69x10^-8 Ohm metres".

Given that p = RA/L, it is clear that R = pL/A = 1.69x10^-8 x L/A. So far, so good. But I am not sure that I can obtain L and A from merely a volume (1cm^3) and a thickness without making some assumption about its shape (a square sheet, perhaps)? Am I missing something?

Thanks!

2. Apr 7, 2005

### jdavel

T7,

What's the resistance of a 1cm x 2cm x 3cm piece of copper?

3. Apr 7, 2005

### T7

Doesn't it depend on which side the current is going through (ie. which sides make up the area)?

4. Apr 7, 2005

### jdavel

t7,

"Doesn't it depend on which side the current is going through (ie. which sides make up the area)?"

Absolutely! So, let's say the current is in the direction of the longest dimension (3cm). What's the resistance of that "wire"?