A circuit diagram uses standard symbols so that anyone can read it. Every component has its own symbol and the wires are drawn as straight lines. A cell is drawn with one long line and one short line. The long line is the positive terminal and the short line is the negative terminal. A battery is two or more cells joined together, drawn as several pairs of lines. In a circuit diagram, conventional current is drawn flowing from the positive terminal of the cell, round the circuit, to the negative terminal.
A switch is drawn as a gap in the wire with a lever. When the switch is open there is a gap, so there is no current. When it is closed the circuit is complete. An ammeter is a circle with the letter A inside and a voltmeter is a circle with the letter V inside. A lamp is a circle with a cross through it and a motor is a circle with the letter M inside.
A resistor is drawn as 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 pointing at a line, and it only lets current pass in one direction. A LED is a diode that gives out light, so its symbol has two arrows pointing away from it. A thermistor is a rectangle with a sloping line through it, and an LDR is a rectangle inside a circle with two arrows pointing towards it.
