Electrical reactance

Electrical reactance. Cross-linked polyalkene. Cross-linked polyethylene. 

If a material has a pure electric resistance property, it is considered an ohmic material and has a constant resistance R largely independent of the potential applied or the current passed through. Other materials that do not comply with Ohm s law have non-linear resistances. Ideal resistors are considered to have no function in storing energy via an electric or magnetic field. However, in AC applications, this is hardly the case because an equivalent inductance or capacitance in series with the resistor element is often considered. The use of AC circuits requires the consideration of additional opposition to current flow due to electrical and magnetic fields treated as electrical reactance effects. An electrical circuit s impedance is defined by the sum effect of resistance and resistance [3]. 

This product can be reduced by reducing X, using series capacitance with a reactance X, which will reduce to - Xq. This is where reactive control plays a major role. By meticulous reactive power manage-ment, the Ferranti effect can be controlled and the electrical line length increased to the desired level. It is a different matter that the electrieal length of the line cannot be raised infinitely, for reasons of stability, as discussed later. 

Strictly, the strain gauges referred to above come into this category, since in such cases the change in the measured quantity causes a corresponding change in the resistance of the element. However, the principle has a much wider application, using changes in either the inductive or capacitive reactance of electrical circuit elements. 

All three of these terms have units of ohms as they are all measures of some form of resistance to electrical flow. The reactance of an inductor is high and comes specifically from the back electromotive force (EMF p. 46) that is generated within the coil. It is, therefore, difficult for AC to pass. The reactance of a capacitor is relatively low but its resistance can be high therefore, direct current (DC) does not pass easily. Reactance does not usually exist by itself as each component in a circuit will generate some resistance to electrical flow. The choice of terms to define total resistance in a circuit is, therefore, resistance or impedance. 

To develop intuition, consider the electric current I (t) flowing in response to the applied voltage V(t). From elementary circuit theory, the capacitive impedance, sometimes "reactance," against this voltage is... 

The non-zero reactance of an equivalent electric circuit results in a phase shift /, which is a difference in the phase of an AC current and AC voltage ... 

The most usual situation that leads to low power factors is the use of inductive motors that, as the name implies, can introduce very large inductive reactance in the line. The electric load introduced by an inductive motor can be represented as a resistance and an inductance in series. This combination will have an intensity vector that will be delayed with respect to the voltage. 

The cell membrane resistance is generally much greater than the reactance of the membrane and is ignored. Likewise the capacitance of the cell cytoplasm can be ignored when its reactance is compared to the cell cytoplasm resistance. The values of the electrical components in the circuit are as follows ... 

Quality factor (Q) - The ratio of the absolute value of the reactance of an electrical system to the resistance thus a measure of the energy stored per cycle relative to the energy dissipated. 

The electric susceptibility can comprise any combination of dipolar, ionic, or electronic polarization processes. This formulation leads to relationships between the real and imaginary parts of the complex electric susceptibility, known as the Kramers-Kronig relationships [28-31] which are very similar to the frequency relations between resistance and reactance in circuit theory [30]. 

Many of the electrical engineering textbooks that include the subject of motors in their contents describe the eqnivalent circnit of an indnction motor as a series and parallel combination of resistances and reactances, see References 1 to 8. The eqnivalent circnit nsnaUy defines the situation for one of the three phases and so care needs to be taken to ensure that the final resnlts obtained apply to the complete motor. Care is also necessary in nsing the ohmic data from mannfacturers, they may have either star winding valnes or delta winding valnes and the choice may not be obvious. The equivalent circuit of most practical use is shown in Figure 5.1 for one star connected winding, where -... 

Steel wire armour as opposed to steel wire braid has lower electrical impedance for a given length of cable. This is an important benefit in networks that are solidly earthed at their power source. Some special applications that require as low an impedance as is practical to achieve in the cable have some of the armour wires replaced by copper wires. Hence the parallel circuit consisting of the steel and copper wires has a lower total impedance than the steel wires on their own. The impedance of the armouring, with or without the copper wires, is predominantly resistive and so the inductive reactance at the power frequency can therefore be ignored. 

The MMW electrical properties of the cavity and the oscillator at resonance are effectively fixed in their manufacture. This treatment addresses the coupling between those two circuit elements to achieve optimal performance. It considers only the circuits at resonance that is, under the working condition of the spectrometer. Recall that the capacitive and inductive reactances in a tuned circuit at resonance cancel each other yielding a purely resistive circuit element. Nonetheless the reactances both still remain and are manifest in the property Q. The treatment will yield the reflection coefficient p of the coupling interface between the cavity and oscillator in terms of their gs and the mutual inductance coupling coefficient M of the impedance transformer that the interface represents. Optimum performance will be when the two circuit elements are critically coupled to each other and that will be shown to occur when p = 0. 

The electronic circuits used with variable capacitance transducers, are essentially the same as any other circuit used to measure capacitance. As with the inductance transducers, these circuits can take the form of a bridge circuit or specific circuits that measure capacitive reactance. One concern with capacitive sensors is that the sensor should be electrically shielded if there are electrically conductive objects in the vicinity of the sensor. Otherwise stray capacitances may affect the measurement. 

Also, deoxyribonucleic acid (DNA) molecules and their electrical conduction have been examined the electrical conduction through DNA molecules (Fink and Schonenberger 1999) and resonances in the dielectric absorption of DNA (Foster et al. 1987). Recently, the Pethig group (Chung et al. 2011) has shown that measurement results in a cell suspension up to iO MHz that is dependent on the cytoplasma membrane capacitance and resistance, the ceU diameter, and the suspension conductivity. By using special interdigitated electrodes, the ceU membrane capacitive reactance sort out the resistance above 100 MHz so that the electric field penetrates into the ceU interior and intracellular dielectric properties can be measured. 

Either the series impedance electrical model (often with the reactance component X neglected) or the parallel equivalent has been used. Several indexes have been introduced to increase the accuracy. Gender, age, and anthropometric results, such as total body weight and height, are parameters used. An often-used index is where H is the body height and the resistance of a given segment. 

If a replacement item has the same technical specifications as the original, then it is generally considered to be In-Kind. The replacement item should have the same materials of construction, rating (pressure, temperamre, voltage, amperage, resistance, and reactance), function, capacity, electrical area classification, and settings. 

Sah [1970] introduced the use of networks of electrical elements of infinitesimal size to describe charge carrier motion and generation/recombination in semiconductors. Barker [1975] noted that the Nemst-Planck-Poisson equation system for an unsupported binary electrolyte could be represented by a three-rail transmission line (Figure 2.2.8fl), in which a central conductor with a fixed capacitive reactance per unit length is connected by shunt capacitances to two resistive rails representing the individual ion conductivities. Electrical potentials measured between points on the central rail correspond to electrostatic potential differences between the corresponding points in the cell while potentials computed for the resistive rails correspond to differences in electrochemical potential. This idea was further developed by Brumleve and Buck [1978], and by Franceschetti [1994] who noted that nothing in principle prevents extension of the model to two or three dimensional systems. 

The main geometrical parameters of a coplanar spiral inductor are the strip width (W), the spacing between adjacent turns (S), the internal radius (Rmt), the number of turns (Nt), the spacing to the surrounding coplanar ground plane (Sg), and the metal thickness (VetaO- A relevant frequency-dependent parameter to measure the overall electrical quality of an inductor is the Q factor obtained when one port is shorted the higher the Q factor is, the better the device electrically behaves. The second parameter, often measured to evaluate inductors, is the self-resonance frequency. A selfresonance occurs when the inductive reactance of the device is equal to the parasitic capacitive reactance between the inductor and the substrate, i.e., if Q = 0. 

In Fig. 1.20 the positive mechanical reactances are symbolized by inductors and negative mechanical reactances are symbolized by capacitors as would be true in the analogous electrical situation. The constant applied force generator is symbolized as a voltage source. Also in Fig. 1.20, Rr is identified as PocSRi 2o>a/c), whereas Kh is identified as poc S /Vq and M, as pocSXi )/o>. Unlike the common electrical situation, however, those elements that stem from radiation phenomena, such as R and M, are themselves frequency dependent. This complication will be dealt with after the model has been more fuUy developed. The circuit of Fig. 1.20, though useful, can only be an intermediate result as it does not involve any of the purely electrical properties of the loudspeaker such as the voice coil resistance or self-inductance. In addition, whenever the voice coil is in motion it has induced in it a back electromotive force (emf) of size Blu that opposes the current in the voice coil. This situation is represented schematically in Fig. 1.21. 

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