Circuit in Series

Determine the total amperage in the circuit. If you had a circuit and you found that it carried a total current of 6 amps, you should use this as the amperage in the circuit. Remember that in a circuit the total amperage is everywhere equal.

Determine the total number of resistance in the circuit. You measure resistance in ohms, which is expressed using the Greek letter omega. If you measure that there is a resistor with 3 ohms of resistance in this circuit and another with 2 ohms of resistance, that means that the circuit has a total resistance of 5 ohms.

Find voltage output by multiplying the amperage by the total number of resistance in the circuit. In the examples above, we know that the amperage is 6 amps and the total resistance is 5 ohms. Therefore, the voltage output for this circuit is:

V=I\times R=6\times 5 = 30\text{ volts}

Circuits in Parallel

Determine the total current in the circuit. Just as it is in a series circuit, the current or amperage is everywhere the same. Using the same example, we'll say that the total amperage is 6 amps.

Find the total resistance in the circuit. The total resistance in a parallel circuit differs from a series circuit. In the series circuit, we obtain the total resistance by simply adding each individual resistance in the circuit; however, in a parallel circuit, we need to find the total resistance by using the formula:

R_{tot}=\frac{1}{\frac{1}{R_1}+\frac{1}{R_2}+...+\frac{1}{R_n}}

That is, one divided by the sum of the reciprocals of all the resistors in the parallel circuit. Using the same example we will say that the resistors have a resistance of 2 ohms and 3 ohms. Therefore the total resistance in this parallel series is:

R_{tot}=\frac{1}{\frac{1}{2}+\frac{1}{3}}=1.2\text{ ohms}

Find the voltage the same way you found the voltage in the series circuit. We know that the total amperage for the circuit is 6 amps and the total resistance is 1.2 ohms. Therefore, the total voltage output for this parallel circuit is:

V = I\times R = 6\times 1.2 = 7.2\text{ volts}