Circuit Diagrams, Circuit Components & Symbols

A circuit diagram is like a map. Lines are wires (paths), and symbols are components. Electric current is like water flowing in pipes. Voltage is the push that drives the flow.

How to read and draw

• Use standard symbols, straight lines, and neat corners.
• Series path: one route for current. Parallel paths: current can split and rejoin.
• Ammeter goes in series to measure current. Voltmeter goes in parallel across a component.

Key components, symbols, and behavior

• Cell/Battery: Cell symbol has one long and one short line. Battery is several cells. Provides d.c. push.
• Power supply / Generator (a.c.): Circle with a sine wave. Push changes direction (a.c.).
• Switch: A gap that can open/close the circuit. Push switch works only when pressed.
• Fuse: Thin wire/small box in series. Melts if current is too large (safety).
• Resistor (fixed): Rectangle. Reduces current.
• Variable resistor: Resistor with a diagonal arrow. You can adjust the resistance.
• Heater: A resistor designed to get hot and warm things.
• Thermistor (NTC): Resistance falls when temperature rises. Used for temperature sensing.
• LDR: Resistance falls when light is brighter. Used for light sensing.
• Lamp: Circle with a cross inside. Glows when current flows.
• Diode: Looks like an arrowhead pointing at a line. Lets current one way only (towards the line).
• LED: Diode with small arrows pointing out (light). Needs a series resistor to avoid damage.
• Motor: Circle with M. Turns electrical energy into motion.
• Ammeter / Voltmeter: Circles with A or V. A in series; V across a component.
• Magnetising coil (solenoid): Coiled wire symbol. Makes a strong magnetic field.
• Transformer: Two coils side by side. Changes a.c. voltage.
• Relay: Coil controlling a separate switch. A small current can switch a bigger circuit.
• Potential divider: Two resistors in series with an output from the middle. Shares the voltage; useful with LDRs/thermistors.
• Electric bell: Symbol shows a bell. Rings when the circuit is completed.