You read an electronic circuit diagram by identifying component symbols, tracing connections, and determining how inputs control outputs. In A3.4, focus on each component’s system function.
A circuit diagram is a functional representation, not a physical-layout picture. Begin at the power supply and trace conventional current from positive to negative or .
| Component | Function in the circuit | Typical system role |
|---|---|---|
| Cell or battery | Supplies electrical energy and potential difference | Power supply |
| Fixed resistor | Limits current or divides voltage | Processing or protection |
| Variable resistor | Provides adjustable resistance | Manual input or control |
| Light-dependent resistor (LDR) | Changes resistance as light intensity changes | Input sensor |
| Thermistor | Changes resistance as temperature changes | Input sensor |
| Diode | Allows one-way current | Control or protection |
| Light-emitting diode (LED) | Produces light when correctly forward biased | Output |
| Transistor | Acts as a switch or amplifier | Processing and control |
| Capacitor | Temporarily stores charge | Timing, filtering, or smoothing |
| Motor or buzzer | Produces movement or sound | Output |
Examine the connections. A junction dot shows connected wires; crossing lines without one indicate no connection. Components on one path are in series, while components connected across branches are in parallel.
Then classify the circuit using the input-process-output model. For example, an LDR detects light, a transistor processes the resulting electrical change, and an LED provides the output. Check polarity carefully for components such as batteries, diodes, LEDs, and some capacitors.
A common misconception is that the diagram shows where components must be physically placed. It shows electrical relationships, not the product’s layout.
For an IB exam response, identify each component, state its function, trace the signal or current, and explain how a change at the input affects the output. Do not merely name symbols; connect them to the operation of the complete electronic system.
