3.5 Circuit Elements and Circuit Diagrams

Reading circuit diagrams

A circuit diagram uses standardized symbols to represent real components: a long/short line pair for a battery, a zigzag or rectangle for a resistor, straight lines for wires, and a circle with a line for a switch or ammeter/voltmeter. Wires connecting components are treated as having zero resistance, so every point along a single connecting wire is at the same potential.

Meters change the circuit differently

An ammeter measures current and is placed in series in the branch of interest; ideally it has near-zero resistance so it doesn't reduce the current it's measuring. A voltmeter measures potential difference and is connected in parallel across a component; ideally it has near-infinite resistance so it draws negligible current, leaving the circuit undisturbed.

Series vs. parallel connections

Components in series share the same current and lie along a single path — if that path breaks, current stops everywhere in it. Components in parallel share the same voltage across each branch, but current can split between branches. Recognizing these arrangements in a diagram is essential before applying Kirchhoff's rules or resistor equations.

Key terms

Circuit diagram

A schematic representation of a circuit using standardized symbols for batteries, resistors, wires, and meters.

Ideal ammeter

A current-measuring device with near-zero resistance, connected in series.

Ideal voltmeter

A voltage-measuring device with near-infinite resistance, connected in parallel.

Series connection

Components along a single path that all carry the same current.

Parallel connection

Components connected between the same two nodes, sharing the same voltage but possibly different currents.

Try an AP-style question

How should a voltmeter be connected to measure the voltage across a resistor?

1. In series with the resistor
2. Anywhere in the circuit
3. Across the battery only
4. In parallel with the resistor