# Measured Surface Resistivity Much Higher than Theoretical Value (Why?)

• LulaBell
In summary, the conversation revolved around a physics lab experiment to measure the surface resistivity of a conductive paper with a carbon filler. The theoretical Rs value for this paper is approximately 5,000 Ω/☐, but the calculated Rs values were found to be much higher at 10,100 +/- 83.07 Ω/☐ and 11,220 +/- 63.02 Ω/☐ when varying length and width, respectively. The group could not explain this large discrepancy and questioned if it was due to the flow of electrons being blocked or if there were errors in their setup. They also discussed the importance of following proper procedures and understanding the theoretical resistivity calculation. They also noted that a sheet
LulaBell
Thread moved from the technical forums to the schoolwork forums
I recently conducted a physics lab to measure the surface resistivity of a conductive sheet of a paper with a carbon filler. The theoretical Rs is approx. 5,000 Ω/☐ for this paper and yet we have calculated two Rs values:

Rs when Varying Length and holding Width = 10100 +/- 83.07 Ω/☐
Rs when Varying Width and holding Length = 11220 +/- 63.02 Ω/☐

To me, this discrepancy is very large, and I can't seem to explain why it could even occur, although we are not the only ones measuring this almost double Rs, it seems consistent around 10,000 Ω/☐ across the entire lab and yet I can't figure out why that is. Does it have something to do with the flow of electrons being blocked? Perhaps we did not connect something right although I struggle to see how that would be consistent with other groups.

Any help is very appreciated.

So what measurement procedures did you use? How does your setup method compare to how the paper is typically used in practice?

Last edited:
Lord Jestocost
Yes the procedures that you followed are important. Also, what do you mean by "theoretical" resistivity? Do you know the model that has been used to calculate it? There might be a factor of 2 in the calculation (and the measurement) that was made to determine it vis-à-vis the way you conducted and analyzed your measurement. Remember that a sheet of paper has two surfaces.

scottdave
Do you have any additional details that may be useful @LulaBell ?

Or were you able to resolve the discrepancy?

## Why is the measured surface resistivity much higher than the theoretical value?

There are several reasons why measured surface resistivity can be higher than the theoretical value. These include surface contamination, improper calibration of measurement instruments, environmental factors such as humidity and temperature, and the presence of surface roughness or defects that are not accounted for in theoretical models.

## How does surface contamination affect surface resistivity measurements?

Surface contamination, such as dust, oils, or other residues, can significantly increase the measured surface resistivity. Contaminants can create additional resistance pathways or insulative layers that alter the electrical properties of the surface, leading to higher resistivity readings.

## What role do environmental factors play in surface resistivity measurements?

Environmental factors like humidity and temperature can have a substantial impact on surface resistivity measurements. High humidity can introduce moisture on the surface, which may either decrease or increase resistivity depending on the material. Temperature changes can affect the intrinsic resistivity of the material and the performance of the measuring equipment, leading to discrepancies between measured and theoretical values.

## How can surface roughness or defects influence measured surface resistivity?

Surface roughness or defects can create localized variations in resistivity. These imperfections can disrupt the uniformity of the surface, causing higher resistivity measurements. Theoretical models often assume an ideal, smooth surface, which may not accurately reflect real-world conditions.

## What steps can be taken to ensure accurate surface resistivity measurements?

To ensure accurate surface resistivity measurements, it is important to clean the surface thoroughly to remove contaminants, calibrate the measuring instruments properly, and conduct measurements in a controlled environment with stable humidity and temperature. Additionally, accounting for surface roughness and defects by using more sophisticated models or measurement techniques can help align measured values with theoretical expectations.

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