Circuits are drawn as diagrams using standard symbols joined by straight lines. In a d.c. circuit the current always flows in the same direction. By convention it is drawn flowing from the positive terminal of the cell or power supply, round the circuit, and back to the negative terminal. A cell is drawn as a long thin line (positive) next to a short thick line (negative). Two or more cells joined together make a battery.
Meters and switches: an ammeter is a circle containing the letter A and a voltmeter is a circle containing the letter V. A switch is drawn as a gap in the wire with a hinged lever that closes it. A filament lamp is a circle with a cross inside.
Resistors: a fixed resistor is a rectangle. A variable resistor is a rectangle with an arrow through it, because its resistance can be changed. A diode is drawn as a triangle with a bar across its point, and current can flow only in the direction the triangle points. An LDR (light dependent resistor) is a resistor rectangle inside a circle with two arrows pointing at it, showing light falling on it. An NTC thermistor is a resistor rectangle with a slanting line through it.
