Series and Parallel Circuits
Series circuits
- There is only one path for current to flow, so the current is the same at every point in the circuit.
- The total potential difference of the supply is shared between the components.
- If one component fails (breaks the circuit), current stops flowing everywhere.
Parallel circuits
- Components are connected across separate branches, so current has more than one path.
- The potential difference across each branch is the same as the supply.
- The current splits between branches: current into a junction equals current out.
- If one branch breaks, current can still flow through the others.
Worked example
Question: Two identical 4 Ω resistors are connected in parallel across a 12 V supply. Calculate the total current drawn from the supply.
Answer: Each resistor has the full 12 V across it, so each branch carries I = V/R = 12/4 = 3 A. The total current is the sum of the branch currents: 3 + 3 = 6 A.
Common mistake: adding the resistances in parallel like they're in series (4 + 4 = 8 Ω). Resistors in parallel combine as 1/Rtotal = 1/R₁ + 1/R₂, which gives a total resistance smaller than either individual resistor, not larger.
