How to combine resistors in series and parallel
Electrical resistance is an important part of electronics. It refers to the degree to which a specially made component prevents the flow of current. Often, a circuit board will contain many connected resistors, and in these cases it is important to be able to calculate the equivalent resistance of all the components. The calculated equivalent resistance depends on whether the resistors are connected in series or in parallel. There are rules that allow the calculation of the equivalent resistance depending on how the individual components are connected.
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Add the total number of resistors in series. The resistors are in series when they are directly connected to each other in a circuit. To calculate the combined resistance of a series of resistors in series, simply add the resistances of the individual resistors. For example, if three resistors are connected in series and each has a resistance of 100 ohms, the combined resistance is 300 ohms.
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Add the total of the resistors in parallel. The resistors are in parallel when they are not directly connected but are opposite each other in an electrical circuit. To calculate the combined resistance of the resistors in parallel, add the inverse of the individual resistance of each resistor. For two resistors in parallel with resistance values of 100 ohms, 1/100 + 1/100 = 2 / 100. Then take the reciprocal of the response, in this case, the combined resistance is 100/2 = 50 ohms.
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Add the combined resistors that are in series and then those that are in parallel. For example, if an electrical circuit has three resistors in series that are in parallel with three resistors in series, and if all resistors have values of 100 ohms, you must first add the resistors in series. For this example, each branch has a combined resistance of 100 + 100 + 100 = 300 ohms. Next, add the different branches in parallel. For this example, 1/300 + 1/300 = 0.0067. Now take the reciprocal, which gives us a total of 1, 641.8 ohms.
