Aerial / antenna: a wire or device used to transmit or receive radio signals.
AC: Alternating Current. AC electricity goes through a series of positive to negative (and back) cycles every second.
AM: Amplitude Modulation. A type of radio transmission that uses variation in the strength (or “amplitude”) of a signal (known as a “carrier wave”) to encode information such as sound.
Amplify: To take a signal and make it larger, for example by proportionally increasing its voltage. If the shape of the signal isn’t faithfully represented when it is amplified, that’s what we know as “distortion”.
Audio transformer: A device that uses coils to transfer audio signals from one part of a circuit to another, while blocking DC voltage.
Base: One of the leads on a bipolar transistor.
Battery: A device for supplying electrical power. Although it’s common to use the term “battery” to refer to any self-contained chemical-based power source, a true battery actually consists of multiple “cells” joined together to provide a higher voltage than one cell alone. Many “watch batteries” aren’t actually batteries, because they’re only a single cell.
Bipolar: A type of transistor. This was the first type of transistor ever made, and it’s still in common use today although it has been replaced in many applications by another type of transistor called a MOSFET.
Capacitor: A component that stores an electrical charge. The amount of charge that can be stored is called the “capacitance.”
Carrier Wave: A radio wave that does not contain any information of its own, but which can be modulated in various ways (such as using Amplitude Modulation or Frequency Modulation) to transmit a signal.
Cell: A device that contains chemicals that react to provide electrical voltage between its terminals. Multiple cells can be connected together to form a “battery”, which has a higher voltage than an individual cell.
Circuit: The collection of wires, components, and connections that work together to provide a certain function. A circuit can be represented using a “circuit diagram”, or “schematic.”
Collector: One of the leads on a bipolar transistor.
Conductor: A material that will allow electricity to flow through it easily. Most metals are conductors. Most non-metals are not. Some types of metal are better conductors than others.
Connection: Where two or more component leads join together to allow electricity to flow.
Crossover: Where two or more wires intersect or pass by each other, but they don’t make an electrical connection because they are insulated from each other.
Current: The movement of electrons along a conductor. By convention, electricity is said to flow from a point of positive voltage towards a point of negative voltage. For example, this can be from the positive terminal of a battery, through a circuit, and to the negative terminal. This is actually the opposite direction to the way electrons move through the circuit, but unless you’re a physicist you don’t need to worry about that distinction!
Dark State: When referring to a light-sensitive component such as an LDR or a phototransistor, the dark state is the normal operation of the device when no light is falling on it. This is the opposite of the “light state.”
DC: Direct Current. DC electricity maintains a consistent polarity, with one point on the circuit always positive relative to the other.
Distortion: See “Amplify.”
Earth (Ground): These two terms are commonly taken to mean the same thing, and refer to the voltage potential of the planet Earth. Most voltage measurements are taken relative to this potential. A point that has a higher potential is said to have a positive voltage. A point that has a lower potential is said to have a negative voltage. Many circuits have a reference voltage labelled “0V” or “GND”, which may or may not be actually electrically connected to physical ground.
Earphone: A device for turning electrical energy into sound waves. These typically have a small coil inside that generates a magnetic field which varies in strength with the signal, and moves a magnet attached to a diaphram to generate sound waves.
Electric Current: See “Current.”
Electrolytic: A type of capacitor that is made with an “electrolyte” inside, and commonly called an “electro.” Electrolytic capacitors are polarised, which means they must be connected the correct way around in a circuit. If an electro is connected to a reverse voltage it can explode, which not only makes a big mess (and can be dangerous) but smells really bad! Always check the orientation of electros before you power up a circuit for the first time.
Emitter: One of the leads on a bipolar transistor.
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Schematic: A method for representing the connections between electronic components in a logical way. The schematic doesn’t need to have any resemblance to the physical circuit, the shape of the parts, or how they are arranged. It should instead the logical operation of the circuit.