The Formula for Calculating Parallel Resistance
2. Demystifying the Equation
Okay, so we know the resistance decreases, but how do we calculate the exact total resistance when resistors are in parallel? Don’t worry, it’s not rocket science (though it does involve a little math). The key is to use the reciprocal formula. Ready?
The formula looks like this: 1/Rtotal = 1/R1 + 1/R2 + 1/R3 + … and so on, depending on how many resistors you have. Basically, you take the reciprocal (1 divided by the value) of each resistor, add them all up, and then take the reciprocal of that sum. Sounds complicated? Let’s break it down with an example.
Let’s say you have two resistors in parallel: one is 10 ohms, and the other is 20 ohms. To find the total resistance, you would do the following:1/Rtotal = 1/10 + 1/20 = 0.1 + 0.05 = 0.15. Then, you take the reciprocal of 0.15, which is approximately 6.67 ohms. So, the total resistance of these two resistors in parallel is 6.67 ohms — less than either of the individual resistors!
While this formula might seem daunting at first, practice makes perfect. Once you’ve worked through a few examples, it’ll become second nature. There are also plenty of online calculators that can do the heavy lifting for you, but understanding the underlying principle is always better!