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# Ohm's Law

Last updated: September 4, 2019

## What Does Ohm's Law Mean?

Ohm’s law states that the current flowing through a conductor is directly proportional to the voltage and inversely proportional to the resistance. The resistance is dependent on the cross-sectional area of the conductor and increases when the conductor wears out due to corrosion and other factors.

Ohm’s law is applied in component selection for electrical circuits and in electrical resistance corrosion monitoring techniques.

Ohm’s law: I = E/R

Where I = current, E = Voltage and R = Resistance

## Corrosionpedia Explains Ohm's Law

Ohm's law is used to determine the component values in electrical and electronic circuits. The various functions of electronic components require the use of different amounts of current and voltage. A resistor is used to control the amount of current and to drop extra voltage, ensuring that the target component’s ratings are not exceeded.

By taking the operating ratings of the components such as a transistor, the value of the resistor required is calculated by Ohm’s law: R = E/I.

Another area where Ohm's law is applied is in an electrical resistance corrosion monitoring technique referred to as the ER probe method. This technique relies on the concept that corrosion on exposed metal leads to a reduction in its cross-sectional area. This reduction causes a resistance increase corresponding to the depth of corrosion.

By monitoring the current flow before and after exposure of the metal, the amount of metal loss can be determined accurately.

Electrical resistance probes make use of two similar conductive elements. The resistance of the corroding sensor is measured and compared to that of a corresponding reference element sealed within the body of the probe. The element temperature is closely matched to reduce the effect of temperature variations.

The sensing element has a composition similar to that of the equipment of interest.

Resistance of the conductor is given by: R = ? (L/A)

Where ? = Resistivity, L = Element length and A = Cross-sectional area of the element.

By making Area (A) the subject, the new cross-sectional area of the sensing element is determined. The material loss due to corrosion is then given by the difference of the two areas. 