Resistors in Parallel

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Components connected in Parallel are wired together as shown in the diagram.

For three resistors ...

R_total = 1 / ( 1 / R₁ + 1 / R₂ + 1 / R₃ )

For just two resistors ...

R_total = 1 / ( 1 / R₁ + 1 / R₂ )

You need to be good at fractions or skilled with your calculator!

On a calculator, to get R_total press these keys ... 1 / ( 1 / R₁ + 1 / R₂ ) =

Test Yourself

Problems like this need to be solved in stages by breaking the problem into simpler parts.

In the diagram below, add R1 + R2 to work out the series resistors.

Then use the parallel resistors formula to work out R3 in parallel with the result of (R1 + R2).

In the next example, work out each of the parallel resistors first and then add the two answers together.

(R1 and R2) in parallel added to (R3 and R4) in parallel.