Glossary

This page provides a glossary of terms.

Summary

The Restart Wiki tries to assume no previous knowledge, only a willingness to learn, and so we try to introduce and explain technical terms as we go along. But you might dip in and out or read the end of an article before the beginning. So this page gathers together as many technical terms as possible, as a single point of reference.

If you prefer, you can also use your favourite search engine or Wikipedia to look up unfamiliar terms.

Glossary of Terms

Term	Meaning
AC	Alternating Current. An electrical supply which reverses direction many times per second. See AC and DC.
Amps (A)	The unit of electric current, i.e. the quantity of electricity passing, a bit like the amount of water flowing in a river. See Electric circuits, volts amps watts and ohms.
Capacitor	An electronic component which can store electric charge. Its capacitance is measured in Farads. See Capacitors.
Bridge Rectifier	Four diodes connected in a square. Applying AC to two opposite corners, you get DC out of the other two. See Linear Power Supplies.
Circuit	Electricity really hates piling up, so it will only flow if it can go around a complete circuit and come back to where it started.
Circuit Diagram	A vacuum cleaner, for example, may contain several paths or "circuits" around which the current can flow, and a computer may contain a huge number. A circuit diagram is a picture of all those paths (or some of them) allowing you to understand how it works.
DC	Direct Current. An electrical supply which goes in one direction only. See AC and DC.
Diode	A 2 terminal electronic component allowing a current to flow in one direction but not the other. See Diodes and Rectifiers.
Electrolytic Capacitor	A type of capacitor which employs an electro-chemical process to achieve a high level of capacitance. See Capacitors.
Electron	A sub-atomic particle carrying a negative electrical charge. A flow of electrons constitutes an electric current.
Farad	The unit of capacitance. See Capacitors.
Field Effect Transistor	A type of transistor where the current flowing between two of its terminals (the source and the drain) is controlled by an electric field created by a voltage on a third terminal (the gate). See Transistors.
Flux	A liquid or paste which helps to remove oxide or other deposits in order to make good solder joints. Only usually needed for challenging soldering jobs such as surface mount as solder normally contains a core of flux.
Henry	The unit of inductance. See Inductors.
Hole	The lack of an electron in a crystal lattice where there should be one. This leaves behind a positive charge. An electron from an adjacent atom can move into the hole causing the hole to move to the adjacent atom. In this way, holes can act like positively charged particles and carry an electric current.
Inductor	A coil of wire, very often wound around a magnetic core, providing a kind of momentum to the flow of electricity. Its inductance is measured in Henrys. See Inductors.
jFET	Junction Field Effect Transistor. A type of field effect transistor where the gate is formed by a semiconductor junction. See Transistors.
Junction Transistor	A type of transistor with 3 semiconductor layers. See Transistors.
Loupe	A magnifying glass, generally without a handle.
MOSFET	Metal Oxide Field Effect Transistor. A type of field effect transistor where the gate is formed by metal deposited on an extremely thin insulating oxide layer. See Transistors.
Multimeter	An electrical test instrument which measures voltage, current, resistance and often several other things. Most usually they have a digital readout but analogue ones with a dial are also available.
Ohms (Ω)	A bit like friction, the unit of resistance to flow of electricity. See Electric circuits, volts amps watts and ohms.
Ohm's Law	The amount of current (Amps) flowing in a circuit is the pressure (Volts) divided by the resistance (Ohms), or I = V / R.
Open Circuit	Electricity likes to go all the way round a circuit and back to where it started. When there is a break in the circuit preventing the current from flowing (maybe due to a fault) this is termed an open circuit.
PAT Test	Portable Appliance Test. This is a basic electrical safety test which should be applied to alll mains operated electrical equipment before and after attempting a repair. It comprises a visual inspection and an automated test. See PAT testing for more details.
Phillips	A type of cross-head screw or screwdriver, similar to but not quite the same as Posidriv.
Posidriv	A type of cross-head screw or screwdriver, similar to but not quite the same as Phillips.
Potentiometer (or Pot)	A resistor with a slider than can be moved along its length from one end to the other to tap off any required amount of resistance, for example for a volume control. See Potentiometer.
Rectifier	See Diode.
Resistor	An electronic component which resists the flow of electricity. It's resistance is measured in Ohms. A resistor always generates heat, even if only a tiny amount, and any replacement must be rated in Watts accordingly. See Resistors.
Resistance	See Ohms.
Schematic	Another name for a Circuit Diagram.
Short circuit	If two wires are touching which shouldn't the electricity may be able to take a short cut, meeting very little resistance and so allowing too much electricity to flow. This is a Bad Thing and can cause things to get hot or even catch fire.
Semiconductor	A material such as silicon, germanium or gallium arsenide which can be made to conduct electricity either by negatively charged electrons (N-type) or by positively charged holes (P-type), by adding small amounts of carefully chosen impurities.
Solder	A mixture (most often) of tin and copper or lead with a relatively low melting point, making it very convenient for making electrical connections.
Spudger	A tool with a thin plastic or metal blade typically used (for example) for inserting into the crack between two halves of a plastic case in order to pry it open.
Surface Mount	A method of manufacture in which electronic components are soldered directly onto the surface of a printed circuit board, as opposed to the older through-hole method.
Through-hole	A method of manufacture in which electronic components are attached to a circuit board by passing their leads or pins through holes in the board and soldering them to the board on the oter side, as opposed to the more modern surface mount technique which allows much higher component densities.
Transformer	Two (or more) coils of wire wound around a magnetic core, used to step a voltage up or down or provide isolation between two circuits. See Transformers.
Transistor	An electronic component with 3 leads used to amplify a signal or switch a current on or off. See Transistors.
Torx	A type of security screw or screwdriver with a 6-pointed star shape.
Volts (V)	The unit of electrical pressure, a bit like water pressure. See Electric circuits, volts amps watts and ohms.
Watts (W)	The unit of power, calculated by multiplying the Volts by the Amps. See Electric circuits, volts amps watts and ohms.