# Electronics Glossary

555 timer IC – a particular type of IC in an 8 pin package, used for timing and signal operations. It contains 25 transistors, 2 diodes and 15 resistors. The 555 is the most popular IC ever manufactured.

Alternating current (AC) – electricity which changes direction in a cyclical fashion. Mains electricity is 50 Hz, which means it changes direction 100 times a second. The rated voltage of AC is not the peak voltage. Mains electricity is 230V AC, but the peak voltage is actually 400V.

Ampere – the unit of current, symbol A. Normally "amperes" is abbreviated to "amps" in common usage. Often milliamps, mA, is used. Measured with an ammeter. 1 ampere is 1 coulomb of charge per second.

Amplifier – a circuit which increases the amplitude (strength) of a signal.

Capacitance – the ratio of change of an electric charge to its electric potential (voltage). Measured in farads.

Capacitor – a component which stores charge; see Components.

Charge – a property of matter which causes it to react to the electromagnetic force. Measured in coulombs.

Circuit – an arrangement of conductors (wires) and components that allow electricity to flow, normally in a loop. A simple circuit is a light bulb connected to a battery.

Conductor – something which allows electricity or heat to pass through it easily. (Also a guy on a train who checks tickets, also a guy who stands at the front of an orchestra and waves his arms to keep them in time.) Most metals are very good conductors, especially silver, gold, copper and aluminium. Some materials conduct electricity only moderately well, like carbon. Non-conductors such as glass and rubber do not conduct well.

Conventional current – for historical reasons "conventional current" flows from positive to negative but electrons are negatively charged, so actually flow from negative to positive.

Coulomb – the unit of charge, symbol C.

Current – refers to the number of electrons in an electrical flow; a greater current means more electrons per second pass a given point in a circuit. Measured in amperes or amps. Note that in the formula V = IR (Ohm's Law), current is represented by I.

Diode – a semiconductor device which lets current through in one direction only. Particular types of diodes are light emitting diodes (LEDs), photo diodes, Schottky diodes, and Zener diodes. See Components.

Direct current (DC) – electricity that flows in one direction all the time; the polarity of the flow does not change.

Efficacy – the actual amount of light produced for a given input power; the number of lumens for the amount of watts used. The efficacy of a candle is about 0.3 lm/W, for the best LEDs roughly 150 lm/W.

Efficiency of a light source – a percentage calculated from the light source's output lumens per watt (lm/W) compared to the maximum possible, 683 lm/W of monocromatic green light at 555 nm, which our eyes using daytime vision are most sensitive to. The best black-body radiator is at 7,000 K, 13.9% (95 lm/W). An ideal 5,800 K black-body, truncated to 400–700 nm (ideal "white" source) is 37% efficient (251 lm/W). To get better than that you have to start dropping wavelengths from the spectrum until you're left with just 555 nm green light. A 100 W, 230 V light bulb is about 2% efficient (13.8 lm/W). A 500W halogen bulb is 2.9% efficient (19.8 lm/W). The best black body radiator is The best CFL bulbs commonly available in New Zealand are about 10% efficient (67 lm/W). Ignoring their power supply, LEDs are presently up to 26% efficient (180 lm/W). This is more than half the theoretical maximum for a white LED of about 44% (300 lm/W).

Electromotive force (emf) – the voltage produced by a voltage source; compare with potential difference.

Electron – a negatively charged sub-atomic particle.

Electricity – a flow of electrons. For historical reasons "conventional current" flows from positive to negative but electrons are negatively charged, so actually flow from negative to positive.

Farad – the unit of capacitance, symbol F.

Insulator – something which does not allow electricity or heat to pass through it easily. Diamond conducts heat ten times as well as aluminium, but is an electrical insulator.

Integrated circuit (IC) – a semiconductor component made of many transistors, diodes, and resistors, and is designed to perform a particular function. Simple ICs have just a handful of transistors, while the most complex ICs have billions of transistors.

Light emitting diode (LED) – a particular type of diode which emits light while operating; see Components and LEDs.

Microprocessor – a computer processor that combines the functionality of a CPU in a single integrated circuit. It accepts input data, processes it according to stored a program, then outputs the result or performs an appropriate action.

Multimeter – a device which can measure a variety of different things (one at a time), including voltage, current, resistance, and sometimes capacitance, the gain of transistors, and the forward voltage of diodes.

Ohm – the unit of resistance, symbol Ω (the capital Greek letter omega). Measured with an ohmmeter.

Ohm's Law – a relationship between voltage, current, and resistance; V = IR.

Parallel – two or more components placed side by side, so that current has to split to flow through them. Compare with series.

Photodiode – a special kind of diode which creates electrical current when light falls on it; one example is a solar cell.

Potential difference (pd) – the difference in voltage (or "potential") between two points, such as the voltage dropped across a component; compare with electromotive force.

Resistance – the ability of a material to impede a flow of electrons. Measured in ohms. For the same voltage, the less resistance, the more current will flow.

Resistor – a substance or component which resists the flow of electricity; see Components.

Schottky diode – a particular type of diode which has a lower than normal forward voltage.

Semiconductor – a chemical element midway between conductors and insulators. By chemically "doping" the semiconductor material an excess or lack of electrons can be created. Also used to describe a category of electronic component, including diodes and transistors. Silicon and germanium are semiconductor elements, with silicon being by far the most common used to make semiconductor components.

Series – two or more components are placed one after another, so that the same current flows through them all. Compare with parallel.

Solar cell – a large area photodiode.

Solar panel – an array of solar cells; more solar cells in series increases the voltage produced.

Transistor – a semiconductor device which can amplify or switch a signal; see Components.

Volt – the unit of electrical force, symbol V. Measured with a voltmeter.

Voltage – the force of an electrical flow. Measured in volts. (To be completely correct it should be called the difference of electrical potential – potential difference – or electromotive force, but in practice pretty much everyone uses voltage, which is certainly easier to remember.)

Zener diode – a particular type of diode which is normally used backward, because when it is reverse biased it breaks down at a set voltage. When that voltage is exceeded it suddenly starts conducting, which clamps the potential difference across it to that voltage.

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