By Paul Mesler Updated Aug 30, 2022
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Ohm’s law is a foundational formula that electricians and physicists use to determine key electrical parameters in any circuit. It is expressed as:
\(V = I \times R\)
where V is the voltage in volts, I is the current in amperes, and R is the resistance in ohms. Resistors limit electron flow, and their material determines the degree of resistance.
In a series circuit, the current is the same at every point. For example, if the circuit carries 6 amps, that is the current to use.
Measure each resistor’s resistance in ohms. If the circuit contains a 3 Ω resistor and a 2 Ω resistor, the total resistance is 3 Ω + 2 Ω = 5 Ω.
Apply Ohm’s law: \(V = I \times R = 6 \times 5 = 30\) volts.
As with series circuits, the current throughout a parallel circuit is uniform. Assume the total current is 6 amps.
Unlike series circuits, the resistances combine reciprocally:
\(R_{\text{tot}} = \frac{1}{\frac{1}{R_1} + \frac{1}{R_2} + \dots + \frac{1}{R_n}}\)
For a 2 Ω and 3 Ω resistor in parallel:
\(R_{\text{tot}} = \frac{1}{\frac{1}{2} + \frac{1}{3}} = 1.2\) Ω.
Using the total current and total resistance: \(V = I \times R = 6 \times 1.2 = 7.2\) volts.
