AC	-	See Alternating Current
ACTIVE COMPONENT	-	One which produces an effect (technical term ‘gain’) of itself. A transistor is an active component.
ALTERNATING CURRENT (AC)	-	Electric current which changes direction with a regular frequency. Domestic mains in the UK have a frequency of 50 Hertz.
ANODE	-	The source of electrons which flow in a current. Normally denoted by ⊕ or +ve sign.
AMPERE(S)	-	A rate of the electric current flowing in a circuit, also the quantity of electricity flowing. One ampere is a current flow of one coulomb per second. Abbreviated to amp or amps.
CAPACITOR	-	A passive component used to store an electric charge. Most commonly two metal plates separated by an insulator of some sort, called a dielectric.
CATHODE	-	The destination of the electrons flowing in a circuit. Normally denoted by O or -ve sign.
CHARGE	-	The quantity of electricity carried by a body or the statement that a body carries an electrical charge which might not be quantified.
CIRCUIT	-	A collection of components, active and passive through which an electric current flows to produce an effect or effects.
COMPONENT	-	One of the items forming part of an electrical circuit, either passive or active.
CONDENSER	-	See Capacitor
CONDUCTOR	-	A material which conducts an electric current well. Most metals are conductors. See also semi-conductors.
COULOMB	-	The S1 unit of electric charge , equal to the quantity of electricity conveyed in one second by a current of one ampere.
CURRENT	-	The movement of electrons. This movement may be singular, e.g., capacitor discharge or continuous (in a circuit) and either alternating or direct current.
DC	-	see Direct Current
DIELECTRIC	-	The insulating part of a capacitor. In small examples it may be mica or paraffin waxed paper. In larger it may be oil or air.
DIRECT CURRENT (DC)	-	Circuit in which the flow of electrons is in one direction only, from anode to cathode.
DRY BATTERY	-	A misnomer for batteries such as carbon zinc (torch battery) in which the electrolyte is not actually liquid, but a paste.
ELECTRODE	-	Any conductor through which an electric current enters or leaves an electrolyte. The casing and central cap of a torch battery are electrodes. The lead plates in a car battery (with dilute sulphuric acid as the electrolyte) are electrodes.
ELECTROLYTE	-	The complementary component in a battery to the metallic components. Usually some sort of acid in liquid or paste form.
ELECTRON	-	A small particle of an atom. An electric current is a flow of electrons.
FREQUENCY	-	In alternating current, the rate at which the current changes direction. One complete cycle is a unit of 1 Hertz, named after the Physicist who researched AC.
HERTZ	-	The unit of frequency (not just electricity, but also, for example, sound waves).
IMPEDANCE	-	A resistor offers electrical resistance in DC circuits, whilst in AC circuits it offers an impedance.
INDUCTOR	-	All electrical currents create a magnetic field around their conductor. In AC the field created in the first half of the cycle can oppose the flow of current (in the opposite direction) in the second half of the cycle. This can be a problem when not wanted, but can be used in an inductor as a type of impedance in AC circuits.
INSULATOR	-	A material which either does not transmit an electrical current at all or only poorly.
PASSIVE COMPONENT	-	Produces no effect of itself but is acted on by the electric current flowing in a circuit, e.g., resistors, capacitors and inductors.
POLARITY	-	The electrical condition or charge of a body, either negative or positive. The central electrode of a torch battery is positive polarity.
RESISTANCE	-	The property of a conducting material (a resistor) to offer an obstruction to the flow of our electric current. Can be calculated by the use of Ohm’s Law.
RESISTOR	-	All substances which conduct an electric current do so to varying degrees. The degree to which they do so is their resistance. The term resistor usually means a component designed to offer a known resistance to the current flow.
SEMI CONDUCTORS	-	Materials which conduct electricity only to some extent and/or under certain conditions.
TRANSISTOR	-	A device in which a small input current alters or affects a large output current. Transistors are made from a semi-conducting material such as silicon or germanium.
VOLT	-	The unit of electrical potential between two points in a circuit.
VOLTAGE	-	The numerical value of the electrical potential across or between any two points in an electric circuit.