Rules:

Series circuit:

1. Same current at all points of circuit (as there are no junctions)

2. E.m.f split between components (Kirchoff’s second law) so: ε = V1 + V2 + V3

3. V = IR, so if I is constant: IR total = IR1 + IR2 +IR3

4. Cancelling the Is gives: R total = R1 + R2 + R3

5. As R = 1/G, you can write this in terms of conductance: 1/G total = 1/G1 + 1/G2 + 1/G3

Parallel circuits:

1. Current is split at each junction so:cI = I1 + I2 + I3

2. Same p.d across all components (three separate loops-within each loop e.m.f = sum of individual p.d.s)

3. So V/R total = V/R1 + V/R2 + V/R3

4. Cancelling the Vs gives: 1/R total = 1/R1 + 1/R2 + 1/R3

5. As R = 1/G, you can write this in terms of conductance: G total = G1 + G2 + G3

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