Electrical impedance in the context of "Acoustic impedance"

The siemens (symbol: S) is the unit of electric conductance, electric susceptance, and electric admittance in the International System of Units (SI). Conductance, susceptance, and admittance are the reciprocals of resistance, reactance, and impedance respectively; hence one siemens is equal to the reciprocal of one ohm (Ω) and is also referred to as the mho. The siemens was adopted by the IEC in 1935, and the 14th General Conference on Weights and Measures approved the addition of the siemens as a derived unit in 1971.

The unit is named after Ernst Werner von Siemens. In English, the same word siemens is used both for the singular and plural. Like other SI units named after people, the name of the unit (siemens) is not capitalized. Its symbol (S), however, is capitalized to distinguish it from the second, whose symbol (s) is lower case.

Johnson–Nyquist noise (thermal noise, Johnson noise, or Nyquist noise) is the voltage or current noise generated by the thermal agitation of the charge carriers (usually the electrons) inside an electrical conductor at equilibrium, which happens regardless of any applied voltage. Thermal noise is present in all electrical circuits, and in sensitive electronic equipment (such as radio receivers) can drown out weak signals, and can be the limiting factor on sensitivity of electrical measuring instruments. Thermal noise is proportional to absolute temperature, so some sensitive electronic equipment such as radio telescope receivers are cooled to cryogenic temperatures to improve their signal-to-noise ratio. The generic, statistical physical derivation of this noise is called the fluctuation-dissipation theorem, where generalized impedance or generalized susceptibility is used to characterize the medium.

Thermal noise in an ideal resistor is approximately white, meaning that its power spectral density is nearly constant throughout the frequency spectrum (Figure 2). When limited to a finite bandwidth and viewed in the time domain (as sketched in Figure 1), thermal noise has a nearly Gaussian amplitude distribution.

In telecommunications and professional audio, a balanced line or balanced signal pair is an electrical circuit consisting of two conductors of the same type, both of which have equal impedances along their lengths, to ground, and to other circuits. The primary advantage of the balanced line format is good rejection of common-mode noise and interference when fed to a differential device such as a transformer or differential amplifier.

As prevalent in sound recording and reproduction, balanced lines are referred to as balanced audio.

A via (Latin, 'path' or 'way') is an electrical connection between two or more metal layers of a printed circuit boards (PCB) or integrated circuit. Essentially a via is a small drilled hole that goes through two or more adjacent layers; the hole is plated with metal (often copper) that forms an electrical connection through the insulating layers.

Vias are an important concern in PCB manufacturing. As vertical structures crossing multiple layers, they are specified differently from most of the design, which increases the chance for errors. They place the strictest demands on registration (how closely aligned different layers are). They are manufactured with different tooling from other features -- tooling that typically has looser tolerances. If either the hole or any layer is slightly out of place, the wrong electrical connections may be made; this may not be visible from the surface. After the hole is drilled, it must also be lined with conductive material, as opposed to simply leaving conductive material in place on copper layers. Even an initially good board may develop problems later because the via reacts to heat differently from the substrate around it. Vias also represent a discontinuity in the electrical impedance, which can cause problems for signal integrity.

An electrical load is an electrical component or portion of a circuit that consumes (active) electric power, such as electrical appliances and lights inside the home. The term may also refer to the power consumed by a circuit. This is opposed to a power supply source, such as a battery or generator, which provides power.

The term is used more broadly in electronics for a device connected to a signal source, whether or not it consumes power. If an electric circuit has an output port, a pair of terminals that produces an electrical signal, the circuit connected to this terminal (or its input impedance) is the load. For example, if a CD player is connected to an amplifier, the CD player is the source, and the amplifier is the load, and to continue the concept, if loudspeakers are connected to that amplifier, then that amplifier becomes a new, second source (to the loudspeakers), and the loudspeakers will be the load for the amplifier (but not for the CD player, there are two separate sources and two separate loads, chained together in series).

A voltage source is a two-terminal device which can maintain a fixed voltage. An ideal voltage source can maintain the fixed voltage independent of the load resistance or the output current. However, a real-world voltage source cannot supply unlimited current.

A voltage source is the dual of a current source. Real-world sources of electrical energy, such as batteries and generators, can be modeled for analysis purposes as a combination of an ideal voltage source and additional combinations of impedance elements.

A short circuit (sometimes abbreviated to "short" or "s/c") is an electrical circuit that allows an electric current to travel along an unintended path with no or very low electrical impedance. This results in an excessive current flowing through the circuit.

The opposite of a short circuit is an open circuit, which is an infinite resistance (or very high impedance) between two nodes.

In electrical power transmission, a transposition tower is a transmission tower that changes the relative physical positions of the conductors of a transmission line in a Polyphase system. A transposition tower allows these sections to be connected together, while maintaining adequate clearance for the conductors. This is important since it distributes electrical impedances between phases of a circuit over time, reducing the problem of one conductor carrying more current than others.

Double-circuit lines are usually set up with conductors of the same phase placed opposite each other. For example, a section of a line may be (top-to-bottom) phases A-B-C on the left, also phases C'-B'-A' on the right. The next section may be B-C-A on the left, also A'-C'-B' on the right. Therefore, the rotation on each side of the tower will be opposite. Transposition helps to reduce the mutual coupling between conductors and between conductors and ground. It also useful in mitigating issues like induced voltages in nearby telephone lines.