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Ag Power Web Enhanced Course Materials

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Ohm's Law - Calculating Resistance

What is Resistance (R)?
Resistance is the opposition of electron flow in a circuit and is based on the physical size of the conductors. Since current is the movement of free electrons in a circuit then the number of atoms in a wire make a big difference as to how many electrons can flow at any given time. The bigger the diameter a wire is, the more atoms there are in the wire, so the more free electrons. The smaller the diameter of wire the fewer the number of atoms so the fewer the number of free electrons.

Resistance Calculation

(R = E ÷ I)

Resistance (R) on the equation is missing and you have the (E) and (I) left. Because they are divided by the horizontal line that means divide the two values.
Simple Circuit

This is a simple circuit with a potential of 12 volts (12 E) and 12 amps (12 I). Use the formula explained on the left side of the page to calculate the voltage.

Since we know the battery is suppling 12 Volts (E), and there is a resistive load of 12 Amps (I) placed in series, the resistance will be:

R = 12(E) divided by 12(I) or R = 1

Click the term to see examples of Current and Voltage.