Circuit Diagrams and Symbols

Circuit diagrams use standard symbols to represent components. Being able to draw and interpret these diagrams is fundamental to all circuit work.

Essential symbols

Component	Description
Cell	Long line (positive) and short line (negative)
Battery	Multiple cells in series
Switch (open)	Break in the line
Switch (closed)	Connected line
Lamp	Circle with a cross inside
Fixed resistor	Rectangle
Variable resistor	Rectangle with an arrow through it
Ammeter	Circle with A
Voltmeter	Circle with V
Diode	Triangle with a line (current flows in direction of triangle)
LED	Diode symbol with arrows pointing outward
Thermistor	Resistor with $\theta$ or a line through it
LDR	Resistor with arrows pointing inward
Fuse	Rectangle with a line through it
Relay	Coil symbol with switch

Rules for drawing circuit diagrams

• Use straight lines with right-angle corners.
• No gaps in the circuit (unless a switch is open).
• Ammeters are drawn in series with the component being measured.
• Voltmeters are drawn in parallel across the component being measured.
• Label all components and values (e.g. 5 $\Omega$, 12 V).

Reading circuit diagrams

To analyse a circuit:

1. Identify whether components are in series or parallel.
2. Find the total resistance.
3. Calculate the total current from the supply.
4. Work out the current through and voltage across each component.

Common errors and how to correct them

• Drawing the voltmeter in series (it must be in parallel).
• Drawing the ammeter in parallel (it must be in series).
• Leaving a gap in a series circuit (no current would flow).

How to apply this in an exam

Draw the circuit neatly using standard symbols. Check that ammeters are in series and voltmeters are in parallel. Label all values.