Lesson focus: seriesDescribes a circuit with only one path, so the components are one after another. and parallelDescribes a circuit with more than one path, so components are on separate branches. connections determine how current divides and how potential differenceThe energy transferred per unit of charge between two points in a circuit, also called voltage, measured in volts (V). is shared.
Apply current and potential-difference rules to compare series and parallel circuits and explain household design.
Build on earlier learning
Potential differenceCurrent and potential difference are now combined to analyse complete circuit arrangements.
Practical
Series and parallel circuits
- Build two bulbs in series, then the same bulbs in parallel.
- Compare the brightness and the ammeter readings.
- Use the model on this page to switch between the two arrangements.
Record: Readings and brightness for each arrangement.
Series and parallel circuits
Choose how the bulbs are connected, add bulbs and change the cell. The meters read like real ones.
Build the circuit
Each bulb has a resistance of 6 Ω (illustrative). Brighter bulbs transfer more energy each second.
You will be successful when you can…
- Identify series and parallel paths.
- Apply current rules.
- Apply potential-difference rules.
- Explain independent parallel operation.
Words that carry the science
- series
- Components connected in one unbranched conducting path.
- parallel
- Components connected on separate branches between the same two points.
- junction
- A circuit point where branches meet or separate.
- branch current
- The current through one parallel path.
- potential difference
- Energy transferred per coulomb between two points.
- total resistance
- The resistance of a single equivalent component replacing a network.
Series circuits have one route for charge
01Series circuits have one route for charge
In a seriesDescribes a circuit with only one path, so the components are one after another. circuit, the same current passes every component. The source potential differenceThe energy transferred per unit of charge between two points in a circuit, also called voltage, measured in volts (V). is shared among components, and the component drops add to the source.
Adding a resistor in series increases total resistanceThe combined resistance of a circuit; for components in series it is found by adding their resistances., so current from the same source decreases. Identical lamps may become dimmer because each transfers less power.
02Parallel circuits provide multiple routes
At a junctionA point in a circuit where the wires split or join., total current equals the sum of branch currentThe current flowing through one branch of a parallel circuit. because charge is conserved. Every branch connected across the same two source terminals has the same potential difference.
Adding a parallelDescribes a circuit with more than one path, so components are on separate branches. branch lowers total resistance and can increase total source current. It does not divide the source potential difference between branches.
03Parallel design supports independent control
Household appliances are connected in parallel so each receives the full supply potential difference and can be switched independently. Each branch needs suitable protection because total current can be large.
The model is simplified: real household circuits include live, neutral and protective conductors, circuit breakers or fuses, and strict voltage-dependent safety rules. Classroom cell circuits should not be connected to mains electricity.
Balance current at a junction
A total current of 1.20 A divides into branches. One branch carries 0.45 A.
- Use charge conservation at the junction.
- Total current = branch 1 + branch 2.
- Branch 2 = 1.20 − 0.45.
- Branch 2 = 0.75 A.
How to make the reasoning visible: The currents recombine to 1.20 A after the branches.
Series-and-parallel circuit
Compare idealised circuits using a 6.0 V source.
| Arrangement | Main current / A | Component p.d. | Observation |
|---|---|---|---|
| one lamp | 0.60 | 6.0 V | reference brightness |
| two equal lamps series | 0.30 | 3.0 V each | both dimmer |
| two equal lamps parallel | 1.20 total | 6.0 V each | both like reference |
| parallel, one switch open | 0.60 total | 6.0 V on active branch | other lamp stays lit |
| series, one lamp removed | 0.00 | no complete loop | both off |
Why is total current 1.20 A for two parallel lamps?
Why does removing one parallel lamp not switch off the other?
Check your understanding
Answer from memory, then check against the suggested answer.
Current rule in series?
Potential-difference rule across parallel branches?
Junction current rule?
A 2.0 A current splits into 0.7 A and a second branch. Find the second current.
Why does adding a parallel branch increase total current from a fixed-voltage source?
Exam Question Practice
Exam Question Practice
Mark points shown after marking
Two identical lamps are connected to the same battery, first in series and then in parallel.
Compare the series and parallel circuits.
(6)Total for this question: 6 marks
Command word: For compareA command word: say how two or more things are similar and how they are different., discuss the same quantities for both arrangements rather than listing unrelated facts.