Current in Series & Parallel
Conservation of Charge: Charge cannot be created or destroyed within a closed system. This means the total number of electrons entering any part of a circuit must equal the number of electrons leaving it.
Kirchhoff's First Law: At any junction in a parallel circuit, the sum of the currents flowing into that junction is exactly equal to the sum of the currents flowing out of it.
Mathematical Expression: For a junction where current splits into two branches and , the relationship is expressed as:
Branch Splitting: When current reaches a junction, it divides among the available branches. The amount of current in each branch depends on that branch's individual resistance.
Resistance Relationship: Current follows the path of least resistance. A branch with lower resistance will carry a higher portion of the total current, while a branch with higher resistance will carry less.
Independent Operation: Because each branch is a separate loop connected to the power supply, components in one branch can often be controlled or fail without affecting the current flow in other branches.
| Feature | Series Circuit | Parallel Circuit |
|---|---|---|
| Number of Paths | Exactly one | Two or more |
| Current Value | Same at all points | Sum of branches equals total |
| Component Failure | All components stop working | Other branches continue to work |
| Control | One switch controls everything | Branches can be controlled individually |
Series Summary: . The flow is like a single pipe of water where the flow rate must be the same everywhere.
Parallel Summary: . The flow is like a river splitting into smaller streams; the total water volume remains the same.
Identify Junctions First: When analyzing a complex circuit, always locate the junctions (points where wires meet) to determine where the current splits or recombines.
Conventional Current Direction: Always assume current flows from the positive (+) terminal to the negative (-) terminal. This helps in tracking the 'in' and 'out' flow at junctions.
Sanity Check: In a parallel circuit, the current in any single branch must always be less than the total current supplied by the battery. If your calculation shows a branch current higher than the total, re-check your junction math.
Ammeter Placement: Remember that ammeters must be placed in series with the component they are measuring to capture the full flow of charge through that specific part of the circuit.