In any electric circuit, the amount of current that can flow depends on the potential difference of the power supply and the nature of the path connecting the loads and power supply. The more difficult the path, the harder it is for electrons to flow through. The measure of the opposition to the flow is known as resistance.
The formula for resistance is R = V / I , in which R is the resistance is in volts / ampere or ohms (Ω), V is the potential difference in volts (V), and I is the current in amperes (A).
This formula was developed by Georg Simon Ohm and the ratio V / I is known as Ohm's Law. Resistance is determined by several factors such as its thickness, length, cross-sectional area, the material, and it's temperature. The measure for the resistance of a substance is it;s resistivity. The gauge number of a wire refers to it's cross-sectional area. The larger the cross-sectional area, the smaller the gauge number.
There are two simple ways to connect conductors and loads. The first one is a series circuit, where the loads are connected one after another in a single path. The second is a parallel circuit, where the loads are side by side.
In a series circuit, the total current is equal to the current of each junction point. The total voltage is equal to the sum of all the potential losses and the total resistance is equal to the sum of all the resistors.
In a parallel, Vt=V1=V2=V3, It=I1+I2+I3, and Rt=1 / R1 + 1 / R2 + 1 - R3
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