Reactance Definition and 11 Discussions

In electric and electronic systems, reactance is the opposition of a circuit element to the flow of current due to that element's inductance or capacitance. Greater reactance leads to smaller currents for the same voltage applied. Reactance is similar to electric resistance in this respect, but differs in that reactance does not lead to dissipation of electrical energy as heat. Instead, energy is stored in the reactance, and a quarter-cycle later returned to the circuit, whereas a resistance continuously loses energy.
Reactance is used to compute amplitude and phase changes of sinusoidal alternating current (AC) going through a circuit element. Like resistance, reactance is measured in ohms, with positive values indicating inductive reactance and negative indicating capacitive reactance. It is denoted by the symbol


{\displaystyle \scriptstyle {X}}
. An ideal resistor has zero reactance, whereas ideal inductors and capacitors have zero resistance – that is, respond to current only by reactance. As frequency increases, inductive reactance also increases and capacitive reactance decreases.

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  1. A

    Adjusting the Power Factor of an RLC circuit

    a) An inductor should be added because that would cancel out the lag of the voltage with the current so that P = IV is at a maximum since V is ahead of I in an inductor b) ##cos(\phi) = \frac{R}{Z}##, ##R = Zcos(\phi) = 60\times 0.5 = 30 ohms## ##X_l - X_c = \sqrt{Z^2 - R^2} = \sqrt{60^2 -...
  2. Mzzed

    Load matching/impedance matching

    Hi all, I am currently working on a project where the output/load consists of both a variable inductance and variable resistance, whilst the circuit driving this load is a class E radio frequency (RF) power amplifier with low resistance but relatively high/medium reactance (attempting to design...
  3. Plat

    High-frequency transformers - how are they different?

    I apologize for being somewhat scatter-brained here, I just have too many questions on this topic. I know high-frequency transformers use ferrite cores instead of laminated silicon-steel, but what other differences are there? Does their reactance still follow the standard formula: 2*Pi*F*L ...
  4. V

    Correcting power factor without affecting active power.......

    When correcting power factor without affecting active power, wouldn't the current and voltage of the system have to change due to Active power =VrmsIrmscos(theta), where cos(theta) is the power factor?
  5. O

    LRC circuit and phase angle

    Homework Statement A 35 mH inductor with 1.0 resistance is connected in series to a 20 µF capacitor and a 60 Hz, 40-V (rms) source. Calculate the phase angle. Homework Equations tan φ = (XL - XC) / R The Attempt at a Solution Solving for φ: φ = tan -1 [(XL - XC) / R] XL = 2πfL = 13.194 Ω...
  6. S

    How do Capacitors and Inductors Add/Remove VARS in AC?

    To my understanding, capacitors cause the current to lead the voltage which adds VARS to the circuit and inductors cause the current to lag behind the voltage which removes VARS (in AC circuits). Also, it is my understanding that VARS increase voltage. I work for one of the largest utilities...
  7. T

    Engineering RLC Circuit

    The question is: The voltage source in the above circuit is a sinusoidal AC source with constant amplitude and constant phase shift but an adjustable frequency. Calculate the frequency ω at which the phasor current I...
  8. T

    Synchronous Machine Transent parameters from sudden 3phase Short Circuit

    Hi, So we're doing this Lab on Transient reactance of a synch generator and I'm reading Sarma's classic: Electric Machines Steady-state theory and Dynamic performance p. 474-479 But I can't see how to get the actual exponential time constants for the sub-transient and transient reactances? Thanks
  9. G

    Where does inductive reactance go?

    Lenz law states the induced emf in any circuit is always in a direction to oppose the effect that produced it. So my question is, 1. Does this mean xl creates a difference in potential and actual electrons flowing in the opposite direction or just oppose the current direction that created it...
  10. Ahmad Kishki

    What is reactive power?

    Complex power has two components the "active" and the "reactive". I am comfused. What is the physical interpretation of the complex component? Also what is the reactance?
  11. EnchantedEggs

    Difference between inductive reactance and inductance?

    Hi All, I'm just trying to get my head around circuit theory at the moment (really, really basic stuff, like what a capacitor is etc) and I've run up against some difficulties in separating out some definitions. The main one I'm wrestling with right now is the difference between the inductance...