Parallel Resistors

Resistors in parallel have an equivalent  (replacement) resistance, Req, given by

            1/Req = 1/R1 + 1/R2 + 1/ R3 + …

 See figure 2.  Note that the voltage across elements in parallel is the same and the sum of the current through all of the parallel legs is equal to the total current in the parallel combination.

            I4 = I1 + I2 + I3