Ohm’s law is an important mathematical formula that electricians and physicists use to determine certain measurements in a given circuit. The formula is:
(V=Itimes R)
where V is the voltage, measured in volts, I is the amount of current measured in amps or amperage and R is the resistance, measured in ohms. Resistors impede the electron flow within a circuit and, depending on their material, offer more resistance than others. The voltage in a circuit is nothing more than “a source of electric potential,” within that circuit.
Circuit in Series
Step 1
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.
Step 2
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.
Step 3
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=Itimes R=6times 5 = 30text{ volts})
Circuits in Parallel
Step 1
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.
Step 2
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}}=1.2text{ ohms})
Step 3
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 = Itimes R = 6times 1.2 = 7.2text{ volts})
