Circuit Symbols & Diagrams
Circuit Symbols & Diagrams
- Every circuit diagram is built from the same small set of symbols.
- The exam never explains them, so you need to recognise each one instantly.
The symbol table
- On a cell, the long thin line is the positive terminal and the short thick line is the negative one. This is the single most misread symbol.
- A battery is just two or more cells drawn together.
- All the resistor symbols start from the same box: an arrow through it means variable, a bent line through it means thermistor, and two arrows pointing at it mean LDR (the arrows are light arriving).
- A diode lets current pass one way only: the way the triangle points.
Reading a circuit diagram
- Start at the positive terminal of the supply and follow the wire. Conventional current flows from + round to −.
- A dot where wires meet is a : the wires are joined there, and the current can split or join.
- An ammeter is connected in the line and a voltmeter is connected across a component. That is the rule for reading diagrams; the reason gets its own page later in this chapter.
- A dashed box around a cell and a small resistor means they are one real battery. The next page explains why a battery is drawn like that.