Section 1 of 7Key rules side by side
| Feature | Series circuit | Parallel circuit |
|---|---|---|
| Paths for current | One loop only | Two or more branches |
| Current | Same everywhere in the loop | Total current splits between branches, then rejoins |
| P.d. across components | Supply p.d. is shared | Each branch gets the full supply p.d. |
| Total resistance | Increases with each extra component | Decreases with each extra branch |
| Effect of a broken component | Whole circuit stops | Only that branch stops |
Section 2 of 7Adding more lamps
Lamps in series
- Lamps in series Each extra lamp adds resistance, so the current falls and every lamp gets dimmer.
- The supply p.d. is divided among more lamps, so each has less.
Lamps in parallel
- Lamps in parallel Each lamp is connected directly across the supply, so its brightness is unchanged when another is added.
- The total current drawn from the supply rises, because there are more routes.
Section 3 of 7Why homes use parallel wiring
1Each appliance on its own branch
- Each appliance on its own branch Every device is connected across the full mains p.d.
2Independent operation
- Independent operation Switching one device off breaks only its own branch.
3Full power available
- Full power available Each appliance receives the voltage it was designed for and works at its rated power.
4Total current adds up
- Total current adds up Running more devices draws more current, which is why circuits have fuses and circuit breakers.
Section 4 of 7Where series is used
Series connection is useful when...
One switch controls everything
- One switch controls everything Safety interlocks and some alarm loops need all parts working for the circuit to be complete.
Sharing p.d.
- Sharing p.d. Cells in series add their p.d.s, giving a larger total voltage, for example four 1.5 V cells make 6 V.
Limiting current
- Limiting current A protective resistor in series with a component reduces the current through it.
Section 5 of 7Answering a comparison question
1
State what is the same and what is different for current and p.d. in each type of circuit.
2
Link the total resistance to the number of components or branches added.
3
Apply it to the context, for example brightness of lamps or whether other devices still work.
4
Support the explanation with a calculation, using V = I × R or the rules for adding resistances where numbers are given.
Section 6 of 7Key terms
| Term | Meaning |
|---|---|
| Series | Components connected one after another in a single loop. |
| Parallel | Components connected on separate branches between the same two points. |
| Fuse | A safety component that melts to break the circuit if the current is too large. |
| Total current | The current drawn from the supply, equal to the sum of the currents in all parallel branches. |
| Supply p.d. | The potential difference provided by the cell, battery or mains. |
Section 7 of 7Exam technique
1
Saying a lamp is brighter in a parallel circuit because 'it gets more current' without giving the reason: it has the full supply p.d. across it.
2
Stating that the total resistance always increases when a component is added; it decreases if the extra component is added in parallel.
3
Mixing up the rulescurrent is shared in parallel, p.d. is shared in series.
4
Forgetting that identical lamps in series share the supply p.d. equally.