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Series and parallel circuits
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Components can be joined in a single loop or on separate branches. The rules for current, p.d. and resistance differ.
Series circuits
One loop. The current is the same everywhere.
The supply p.d. is shared between components.
Total resistance: R = R1 + R2.
The supply p.d. is shared between components.
Total resistance: R = R1 + R2.
Parallel circuits
Separate branches. The p.d. across each branch equals the supply p.d.
The currents in the branches add up to the total current.
Adding a resistor in parallel reduces the total resistance, because there are more paths for the current.
The currents in the branches add up to the total current.
Adding a resistor in parallel reduces the total resistance, because there are more paths for the current.
Comparing them
A 4 Ω and a 6 Ω resistor are in series with a 5 V cell. Find the current.
- Total R = 4 + 6 = 10 Ω
- I = V ÷ R = 5 ÷ 10
Answer: 0.5 A
Series: same current, p.d. shared, resistances add. Parallel: same p.d. on each branch, currents add, total resistance goes down.
The interactive lesson includes the diagrams for this topic.
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