Questions tagged [reactance]

The opposition of a circuit element to a change of electric current or voltage, as happens in capacitors and inductors.

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33 views

Capacitive reactance related to frequency

Why does capacitive reactance decrease with the increase of the frequency of the applied signal? It is easy to prove why capacitive reactance decreases with increased capacitance. The more we increase ...
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22 views

In a RCL circuit; where V_C > V_L is the phasor angle leading or lagging?

Is this example correct in stating that the phasor angle is leading by 38.323deg?
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54 views

Why can't i calculate the Inductive reactance in this way?

Question: \$V_1=40sin(1000t)\$,what is the value of Inductive reactance? Solution : \$Z=\frac{V_1}{I}=\frac{40}{8}=5\$,so \$5=\sqrt{R^2+X^2_L}=\sqrt{4^2+X^2_L}\$,so \$X_L=3\$ But i want to ask ...
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233 views

What is the reactance when the frequency is 80 kHz?

I recently had a test with the following question: What is the reactance of a 6.8µF capacitor at 80 kHz I found the reactance to be: \$X_c=\frac{1}{j \cdot 2\pi \cdot f\cdot C}=\frac{1}{j \cdot 2\...
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45 views

Thevenin resistance in a fault current

In the reactance diagram, why is j0.20 (as circled in the picture) in series with j0.20 + j0.10 + j0.17. Why isn't j0.20 (circled) in parallel with j0.20 + j0.10 + j0.17 and j0.20 + j0.1333 + j0.24.
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43 views

Series Resistance-Capacitance Circuit

I have an optocoupler and I connect it to 230V, the datasheet tell me the optocoupler has a forward voltage: IF = ± 5 mA VF - 1.5 V, so, for limiting the current I need an resistor of 4.7K - 11wats, ...
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34 views

Current when switching on with inductance. Role of Reactance?

When switching on the current through a coil it can be described as: \$ I(t) = \frac{U}{R} \cdot (1 - e^{(-x\cdot R/L)}) \$ For a sinusiodal current the complex resistance for a circuit with ...
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140 views

Heating vacuum tube filament via capacitor

As I understand vacuum tubes (like triode / pentode) usually are designed to be heated with certain current through the filament. And usually it is about low-voltage and comparatively high-current. E....
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87 views

Electrical RL circuit problem

So I am given u(t)=325sin(314t+90°)V i(t)=14.14sin(314t+30°)A I have to find the impedance Z∠θ, value for the resistor and inductor, inductive reactance Urms∠θ = 325/sqrt2 ∠90° Irms∠θ = 14.14/...
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46 views

How to calculate reactance from an impedance analyzer circuit?

Background I have an impedance analyzer that uses the below circuit: Source One can measure impedance of the device under test (DUT) by using the following formulas: ...
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1answer
153 views

Foster's Reactance Theorem - Reactance Increasing with Frequency?

I'm currently reading a text on analog filters (Zverev) that discusses Foster's Reactance Theorem in relation to passive circuits and I was thrown a little by the text that says: "Physically, this ...
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47 views

Total phase inductance of three phase reactor

Consider a three phase reactor (inductor) using E-I or E-E laminations with phase winding on each limbs. Now inductance of R phase is given by: Lr=Lrr+Mry+Mrb Lrr: Self inductance of R-phase Mry: ...
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86 views

The resistance and magnetising reactance of the core

I did an experiment where I varied the test voltage and determine the values of the resistance and magnetising reactance of the core. What I noticed is that their values actually vary (not constant). ...
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3answers
90 views

Under open-circuit conditions, does a transformer behave more like a resistor, capacitor, or inductor?

I have the below schematic showing the equivalent circuit of a transformer under open-circuit conditions. Will the transformer behave like a resistor, inductor, or capacitor? And will this behaviour ...
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128 views

Crockcroft-Walton Voltage Multiplier Large Voltage Loss

I have a CW voltage multiplier that uses 30kV, 1nF capacitors and doubled 20kV, 5mA, 100ns diodes (for a total of 40kV). My ac source is a sine wave (viewed on the primary side of the transformer ...
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118 views

Are my calculations wrong for the capacitance?

In an earlier post i discussed about the effects of voltage derating on a capacitor. From here i measured the output with DC and AC applied to a highpass filter and found the cutoff frequency with the ...
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How to calculate the reactance of a capacitor with an input signal that is 2 sin waves of difference frequencies added together?

I am trying to calculate the reactance of a capacitor with an input signal that is not a single frequency. For example, x = sin(4t)+sin(5t), or a capacitor that is used in an audio circuit like the ...
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1answer
155 views

what does low reactance mean physically

What does "lower" reactance (higher susceptance) mean for a physical system, and when is it "good"? I see that it has less opposition to a change in voltage or current, but what does that mean? Lower ...
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1answer
527 views

Peak Current vs RMS Current when calculating Reactance

I am having a hard time getting a grip on AC circuit analysis. I have been taking my peak voltage/current and converting it to RMS current and RMS voltage so I can use ohms law and things like that to ...
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106 views

Voltage in RC circuit with unknown frequency

We were given the task of finding the voltage drop across R1 of the circuit below with the following alternatives: 5.8V 4.8V 4.0V 10.0V All given information is contained within the image, i.e. no ...
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473 views

Capacitor Reactance/Impedance Confusion

I always thought that capacitors (when used in phasor analysis) just had an impedance of $$1/jwc$$. I understand that impedance $$Z=R+jX$$where R is resistance and X is reactance. Now, in one book I ...
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132 views

Nonzero current at voltage zero-crossing when consuming reactive power

In a circuit that consumes some reactive power, the current waveform indicates current flow even when the supply voltage is at the zero crossing. This seems paradoxical since there cannot be current ...
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4answers
537 views

Does reactance increase noise?

Impedance is made of resistance and reactance which is capacitance and inductance. I read that increasing resistance increases noise, but what if capacitance or inductance is increased, does the noise ...
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75 views

Trying to analyze the audio attenuation.. Is this analysis correct?

I am learning about impedance. So sorry any stupid question here... Consider this circuit: I have an audio input, from 20 to 20 kHz. I want to know how the AC voltage over AB will behave as the ...
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205 views

For an ideal Capacitor, when is the current leading and when is the voltage leading by 90?

Say I have a purely restive load as a reference in parrallel with an ideal capacitive load. I know that the current through the capacitor is said to be leading by 90 degrees. Specifically though, what ...
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169 views

Rectangular Waveguide H-Plane Step Discontinuity - Equivalent Reactance for Change in Height

I have been reading Pozar's Microwave Engineering, and in Section 4.6, he goes through the analysis to determine the reactance of a discontinuity between two coupled waveguides. In that chapter, he ...
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1k views

What's the relationship between susceptance and reactance?

I was trying to find the relationship between these two online, but I found out two completely opposite answers, and I'm wondering which one is the right one. Is B = -1/X or is B = 1/X ?
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382 views

Why inductive reactance has two formulas

We know inductive reactance XL will have two formulas. One is XL = 2piFL and other is XL = V/I (Ohm's law). Why we have 2 formulas for inductive reactance. Is the solution ( inductive reactance value)...
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3k views

What is the difference between Instantaneous current (i) and current (I) in a purely inductive circuit?

I was reading about AC inductor circuits on All About Circuits: Link: https://www.allaboutcircuits.com/textbook/alternating-current/chpt-3/ac-inductor-circuits/ Consider this circuit of a purely ...
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3k views

Why does an induction motor draw more current when the load is increased?

I am aware that a coil has inductive reactance when powered by AC besides the еlectrical resistance which is typically very low. Considering the fact that reactance is proprotional to the inductance ...
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633 views

Does leakage reactance of transformer depend on quantum of load?

In a single phase transformer, considering copper losses and core losses, I want to find whether the leakage reactance is affected by change in load on the secondary? I was unable to find an answer ...
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Is the formula for inductive reactance the same when considering rectified AC?

Is the formula X\$_L\$ = 2\$\pi\$fL still true for rectified (but unfiltered) AC (in which case the frequency f, and therefore the reactance, would be doubled in the case of full-wave rectification)? ...
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264 views

What frequency is Ferrite Bead reactance usually given at?

I've noticed on schematics at work, when I was at uni, and on datasheets that Ferrite Beads usually (90% of the time) are only given with their designator (FB? or L?), then the reactance (XOhms) and ...
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3k views

Voltage across capacitor/inductor in RLC circuit

It is said that voltage across capacitor/inductor is higher than the applied AC voltage. How?
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256 views

capacitive reactance in a stranded wire

Can a stranded wire exhibit a capacitive reactance? I measured the real and imaginary part of a piece stranded wire using an old LRC meter( HP 4284a). Applied an open loop and a closed loop ...
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454 views

Understanding loudspeaker impedance

If I am correct, a typical loudspeaker's impedance will change depending on frequency. The impedance will be comprised of the resistance and the reactance of the voice coil. As frequency increases, so ...
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249 views

Properties of an Ideal Transformer and the reasons behind them

Why should the magnetising reactance of an ideal transformer be very large i.e. approach infinity? What practicality does this imply?
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At what frequency will the reactance of a 200mH inductor will be 5kΩ? [closed]

I'm doing practice exam questions, I have no idea what formula applies to this question. I know Xl = 2πf*L, but the question is asking for the frequency, how can I complete this when the formula for ...
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438 views

Gain factor in real Resistance and Reactance (AD5933)

I'm trying to develop a system for bioimpedance measurement with the IC AD5933. The AD5933 is a high precision impedance converter system that combines a frequency generator with a 12-bit, 1 MSPS, ...
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4answers
284 views

Is current calculation in copper wire for AC simple or not?

I'm trying to learn electronics by myself, and I'm starting with simple current calculations. Let's assume we have a straight wire of length L connecting a source and a sink. I know the voltage (V), ...
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1k views

Why inductive and capacitive reactances have opposite signs and why they cancel out eachother?

For example in a series RLC circuit with ac source why total reactance is inductive reactance minus capacitive reactances ? I dont need any mathematical proof. Can anyone provide me a a logical ...
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484 views

Complex reactance formula explanation

Can someone explain the math behind the following relationships between the equalities in a capacitor's reactance? $$X_C = \frac{1}{2\pi f C} = \frac{-j}{\omega C} = \frac{1}{j \omega C}$$ For ...
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120 views

Finding total impedance

I have a circuit as shown below simulate this circuit – Schematic created using CircuitLab Where R1, R2 are resistors. jX1 and jX3 are reactants, and jB2 is admittance. That being said, I'm ...
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How can AC current be limited with reactance?

Since resistor dissipate electrical energy by converting it to heat, while capacitors and inductors store electrical energy I believe using reactance will waste less energy. My source is 225 V, 50 Hz....
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55 views

How do I use series and parallel combinations of inductors and resistors to achieve a certain resistance+inductance?

I'm building a current driver for a load of characteristics 20mH and 5ohms. I don't have the load with me so I'm trying to create it using inductors + resistors so I can test my driver ckt. I have ...
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55 views

Induction Motor - Reactances and Leakages

In the induction motor equivalent circuit (either Thevenin or otherwise), the rotor, and stator leakages and reactances are necessary for any useful calculations. How does one estimate leakages and ...
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103 views

Calculation of the input impedance of reactance modulator

The figure 1.36 is a circuit of reactance modulator which is equivalent to a tunable inductance. I know the input impedance expression is Zin = (Z1 + Z2)/(1 + gm*Z2), but how to derive this expression?...
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2k views

What effect does Permanent Magnet have on an air-core coil?

Given an air-core coil of known inductance and a given frequency of applied voltage, you can predict the coil reactance, the current, and the voltage/current phase relationship. What effect, if any, ...
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7k views

How to Derive Capacitive- and Inductive Reactance Formula

I've been searching around the internet to find out how to derive the reactance formula for capacitors and inductors. But I couldn't really find anything, so I thought why not make a post about it. ...
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51k views

How do I find C & L from XC and XL?

Calculating Capacitance and Inductance from Capacitive Reactance and Inductive Reactance I'm trying to find the inductor (L) and capacitor (C) values using the inductive reactance (XL) and capacitive ...