Resistivity measurements of a circular shaped sample

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Discussion Overview

The discussion revolves around the calculation of resistivity for a circular-shaped sample using two-probe measurements. Participants explore the necessary formulas and considerations related to the geometry of the sample, including its thickness and the need for correction factors.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant seeks guidance on the appropriate formula for calculating resistivity of a circular sample using two-probe measurements, emphasizing the inclusion of thickness and correction factors.
  • Another participant suggests that resistivity can be derived from DC resistance measurements and the sample's geometry, noting that the term "circular shape" is ambiguous.
  • A participant points out that measuring resistivity across a disk or ball-shaped object requires solving the Coulomb-Bousinesq equations, indicating the complexity of the three-dimensional nature of the problem.
  • Clarification is provided that the sample is a circular disk with a thickness of approximately 1mm, and the participant mentions existing formulas for other configurations like Van der Pauw and collinear four-probe methods.
  • Further details are provided about the sample being a circular pellet with a thickness of 0.6mm and a diameter of 13mm.

Areas of Agreement / Disagreement

Participants express varying degrees of understanding regarding the geometry of the sample and its implications for resistivity calculations. There is no consensus on a specific formula for the two-probe method applicable to the described sample.

Contextual Notes

The discussion highlights the need for clarity in defining the geometry of the sample, as well as the potential complexities involved in applying the two-probe method to a circular disk shape.

brk
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Hai,
I am doing my masters degree in physics. can somebody help me in which formula to use for calculating resistivity of a sample of circular shape using two probe measurements, which should include thickness and correction factor also.
Thank You!
 
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Welcome to PF;
You should be able to get the resistivity from a measurement of the DC resistance across the sample and it's geometry. Which direction you take the resistance measurement depends on the specifics of your samples shape. "circular shape" is a little vague.
 
thanks for the reply...
I measured the dc resistance already,but how to calculate the resistivity for a circular sample. Using two probe method.
 
how to calculate the resistivity for a circular sample. Using two probe method.
Nov12-12 04:09 AM

Circular is a 2 dimensional shape. You have lost one dimension.

It is usual to choose the measurement sample so that it is long compared to its cross sectional area (ie along a length of wire) so that the effect of the spread of current may be ignored.

If you are measuring across a disk or ball shaped object then you will have to set up and solve the Coulomb-Bousinesq equations, using your dimensions as boundary conditions. Hertz solved these in about 1885.

However it is a three dimensional problem so you need to be clear as to the geometry.
 
Studiot said:
Circular is a 2 dimensional shape. You have lost one dimension.
I was going to say - yeah ... "circular volume" is sometimes used to describe a flat cylinder though - like a coin is "a circle" in common language, right?

Still, I did try to prompt for this:
me said:
...measurement depends on the specifics of your samples shape. "circular shape" is a little vague.
... maybe that should have been an explicit question. OK. What is the 3D geometry of your sample?

Otherwise the best anyone can do is describe the 2-probe method in general.
 
i understood what you are trying to convey!
it is circular disk shaped sample of thickness of 1mm or so. The resistivity of the sample is very high, so we preferred to measure using two probe method. There are formulas for vanderpauw, collinear four probe configurations to calculate the resistivity from the measured voltage. Similarly i need a formula for two probe configuration to calculate the resistivity of circular disk shaped sample.
 
You still didn't answer the question about the geometry.
 
it is circular pellet of thickness 0.6mm and diameter 13mm.
 

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