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Resistors in Parallel

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Everyone

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

ResistorsInParallel.gif

For three resistors ...

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

For just two resistors ...

Rtotal = 1 / ( 1 / R1 + 1 / R2 )

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

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

Test Yourself

Combined Series and Parallel

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.

Resistors-series-and-parallel-1.GIF

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

Another Series and Parallel Calculation

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

Resistors-series-and-parallel-2.GIF

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

 

 

 

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