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1. Measuring resistivity of glass
So lets say I have different glass sheets of set thickness but varying cross sectional area.

I apply a PD across them of set magnitude and determine their resistances.

Using the formula :

R = rho*l/A

I plot a graph of R against 1/A.

But what is A ? is it the full cross sectional area of the glass sheet ?

A question like this came up in an exam paper and the mark scheme said the following :

Method of determining area perpendicular to current flow.

Why the special emphasis on perpendicular ? Wouldn't it just be the length times the height of glass sheet ?
2. Re: Measuring resistivity of glass
(Original post by Ari Ben Canaan)
So lets say I have different glass sheets of set thickness but varying cross sectional area.

I apply a PD across them of set magnitude and determine their resistances.

Using the formula :

R = rho*l/A

I plot a graph of R against 1/A.

But what is A ? is it the full cross sectional area of the glass sheet ?

A question like this came up in an exam paper and the mark scheme said the following :

Method of determining area perpendicular to current flow.

Why the special emphasis on perpendicular ? Wouldn't it just be the length times the height of glass sheet ?
The glass sheet is a very thin rectangular block.
If you imagine a more normal rectangular block like a gold bar, for example, and you were asked to pass a current through it, you could do this 3 ways depending which pair of faces you connected to the terminals to.
The mark scheme is just making the point that the area in the formula is the one into which you pass the current.
3. (Original post by Stonebridge)
The glass sheet is a very thin rectangular block.
If you imagine a more normal rectangular block like a gold bar, for example, and you were asked to pass a current through it, you could do this 3 ways depending which pair of faces you connected to the terminals to.
The mark scheme is just making the point that the area in the formula is the one into which you pass the current.
Oh, good, I thought I'd missed something.

Thank you.

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