Circuit diagram questions appear in both Paper 2 and Paper 4. Marks are lost when diagrams are unclear or use non-standard symbols.
Standard circuit symbols
You must use the symbols specified in the Cambridge IGCSE Physics syllabus. The main ones are:
- Cell: two parallel lines (long thin = positive, short thick = negative)
- Battery: two or more cells in series
- Switch: a gap with a hinge contact
- Resistor: a rectangle
- Variable resistor: a rectangle with an arrow through it
- Lamp: a circle with a cross inside
- Ammeter: a circle with A inside, always connected in series
- Voltmeter: a circle with V inside, always connected in parallel
- Thermistor: a rectangle with a line through it (temperature-dependent)
- LDR: a rectangle with arrows pointing towards it (light-dependent resistor)
- Diode: a triangle pointing to a line (current flows in triangle direction)
- LED: a diode with small arrows pointing away
Drawing rules
- Use a ruler for all straight lines.
- Wires connect at right angles; use dots at junctions.
- Leave space between components so the diagram is easy to read.
- Label each component or use a key.
- Close all loops. An open circuit is incorrect unless the question specifically shows a switch.
Parallel circuits
Draw parallel branches clearly. A common error is drawing two components on separate branches but failing to show where the branches join back together. Both branches must reconnect to the same wire before returning to the cell.
Checking your diagram
Before moving on, trace the path from the positive terminal of the cell through every component and back to the negative terminal. If you cannot trace a complete loop, the circuit is incomplete.
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