Logic gates process signals which represent true (1, high, +Vs, on) or false (0, low, 0V, off). For more information please see the page on logic gates. There are two sets of symbols: traditional and IEC (International Electrotechnical Commission).
Zener diode A zener diode can be used to maintain a fixed voltage.
The diagram shows a simple circuit of a battery, wires, a switch and a lamp. The switch works by breaking the circuit.
This type of variable capacitor is designed to be set when a circuit is made and then left without further adjustment.