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Physics 06254.3 Electric circuits

Series and parallel circuits

Wire resistors in series or parallel and watch the total resistance, current and branch currents update.

  • Series and parallel resistance
  • Current in branches
  • Potential difference sharing
6 Ω3 Ω8.0 V4.0 Vsame current everywhere: 1.33 A12 V

Total resistance

9.00Ω

Total current

1.33A

Through R₁

1.33A

Through R₂

1.33A

Predict

Two 6 Ω resistors are connected in parallel. What is the total resistance?

Experiment

  1. 1Set both resistors to 6 Ω in series, then switch to parallel. Compare the totals.
  2. 2In series, check that the two p.d.s add up to the supply voltage.
  3. 3In parallel, check that the two branch currents add up to the total current.

Explain

In series there is one path, so the current is the same everywhere and the supply p.d. is shared in proportion to resistance. Resistances add: R = R₁ + R₂.

In parallel each branch gets the full supply p.d., and the current splits. Because there are more paths for the charge, the total resistance falls: 1/R = 1/R₁ + 1/R₂.

A useful sanity check in an exam: a parallel total that comes out larger than the smallest branch resistance is always wrong.