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ruchika
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how does contact resistance and sprearding resistance gets in eliminated in four probe technique for measuring resistivity in comparison to two probe technique where we encounter these resistances?
f95toli said:It should be fairly obvious if you draw a circuit diagram.
In the ideal case (perfect current source and voltmeter with inifinite input impedance) the series/contact resistance is eliminated simply because the current is the same in the whole circui (no current flows into the voltmeter) and the voltmeter is only measuring across the sample.
Since you know the current and the voltage you then calculate the resistance from Ohms law
Note that there are of course instances where non-ideal effects come into playl; e.g..when measuring samples with very high (several megaohms) or low resistance (milliohms); so it is important to understand how the technique actually works.
Edit: I just realized that I assumed you were referring to "through" measurements (e.g. a resistor), but since you are referring to resistivity you might actually be asking about van der Paw measurements (of e.g. thin films)?
The four probe method is an electrical measurement technique used to determine the resistivity or conductivity of a material. It involves applying a current through two outer probes and measuring the voltage drop between two inner probes, allowing for more accurate measurements than traditional two probe methods.
The four probe method eliminates errors caused by contact resistance and allows for precise measurements of electrical properties, even in highly resistive materials. It also minimizes the effects of temperature and sample geometry, making it a more reliable method for determining resistivity.
Compared to the traditional two probe method, the four probe method yields more accurate results by eliminating the effects of contact resistance. It also outperforms other techniques, such as the Van der Pauw method, in terms of accuracy and reliability.
The four probe method is applicable to a wide range of materials, including semiconductors, metals, and insulators. It can also be used to measure the electrical properties of thin films, multilayer structures, and nanomaterials.
One limitation of the four probe method is that it requires precise positioning of the probes, which can be challenging for small or irregularly shaped samples. It also requires specialized equipment and may not be suitable for in situ measurements.