Questions tagged [reactance]

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

Filter by
Sorted by
Tagged with
0 votes
1 answer
34 views

Can admittance (Y) be used to calculate reactance when L and C values are calculated from the Y12 and Y11 parameters like normal as X=XL-XC?

My original question sought to understand the relationship between S-parameters and reactance. In the process of trying to figure that out, this second question arose. The actual question is at the ...
user avatar
  • 872
0 votes
1 answer
57 views

How are S-Parameters and Reactance related, can one be calculated from the other?

I know that, for example, \$X_L=2\pi f L\$ will calculate reactance of an ideal inductor, but can this be calculated for a real component model? Given the S-Parameter values at some frequency from an ...
user avatar
  • 872
3 votes
3 answers
296 views

Should I include the resistance of capacitors and inductors (reactance) in my schematic?

I generated a DC/DC PS circuit from Maxim Integrated, and got this output: You'll notice that both the inductors and the capacitors have their respective resistances marked (in milliohms). Are these ...
user avatar
-2 votes
1 answer
81 views

Why does this method of measuring inductance work? [closed]

I recently watched this video from EEVblog showing a method of measuring inductance. I'm probably missing something obvious, but why does this work? Mathematical proof would be great. Thanks. https://...
user avatar
0 votes
0 answers
47 views

How to measure the output of a ceiling fan controller?

Background: I have an older home automation system that I'd like to use for controlling my gas fireplace (flame and fan separately). Due to the automation system's age (and unknown manufacturing ...
user avatar
1 vote
1 answer
58 views

Determining the impedance of an unknown component

If I have an antenna and I wish to measure its impedance. I have two impedance values, Z=125.52-j207.36Ohms and Z=8.14-j39.6Ohms, and I do not know which one is correct/ which one applies to this ...
user avatar
  • 340
0 votes
0 answers
50 views

Variable capacitive dropper power supply by means of capacitor switching with TRIAC?

Is it possible to increase the reactance and thus the current of a capacitive power supply by switching an additional capacitor in parallel using a TRIAC (e.g. zero-crossing SSR)? simulate this ...
user avatar
  • 395
1 vote
3 answers
93 views

Will DC with a frequency have reactance?

I am getting mixed answers for the question. Quora says: There is no reactance! Xc = 1/(2 x pi x f x C), and since f=0, Xc = 0. The frequency is non-zero (for second and third picture,) though. Then ...
user avatar
9 votes
6 answers
2k views

What is the difference between impedance and reactance?

I mean how are they physically different? What does it mean to have imaginary numbers in the reactance?
user avatar
  • 121
2 votes
1 answer
192 views

About power dissipation of capacitors and inductors & I-V phase difference

For instance, The Art of Electronics (by Horowitz & Hill) states that ideal capacitors cannot dissipate power, even though current can flow through them, because the voltage and current are 90° ...
user avatar
  • 23
1 vote
1 answer
105 views

How to relate resistance/reactance to parallel/series equivalent circuits?

Problem 7A of The Electronics of Radio asks the reader to find the relationships between resistance and reactance values in any arbitrary series/parallel circuit and their counterparts in a parallel/...
user avatar
  • 135
0 votes
1 answer
68 views

What is the capacitive reactance in this case?

Capacitive reactance in ohms is defined as: $$X_C(\omega) = \frac{1}{2\pi f C}$$ where the unit of C is farad. Focusing on the frequency \$f\$ in the equation: If the input signal to the capacitor is ...
user avatar
  • 3,420
8 votes
2 answers
1k views

How can you do "impedance matching" on USB or other serial communication lines?

I was told that that impedance matching is important when going to high speeds on USB. I assume that the "impedance" matching in practice means "reactance" matching. But, how can ...
user avatar
  • 189
0 votes
0 answers
84 views

Why reactance is imaginary? [duplicate]

In AC circuit, cartesian impedance formula is Z = R + jX (Z = impedance, R = resistance, X = reactance). Why is reactance imaginary (for capacitors and inductors)? I cannot find a good explanation ...
user avatar
3 votes
1 answer
209 views

Proof of capacitive reactance equation

I have a doubt about the ratio of potential difference and current of capacitor $$X_c = \frac{v}{i} = \frac{1}{\omega C}$$ If I have a sinusoidal potential difference $$v = V_Msin(\omega t)$$ and the ...
user avatar
  • 133
1 vote
2 answers
288 views

Why is an infinite reactance an open circuit?

I'm writing up a summary about classic impedances (resistors \$Z_R=R\$, capacitors \$Z_C=1/j\omega C\$ and inductors \$Z_L = j\omega L\$) for students starting out with AC networks. I was about to ...
user avatar
  • 129
0 votes
0 answers
21 views

Coupling coefficient in function of reactance

If there are two coupled inductances L1 and L2, we may want to write k in function of the reactances, that is, in function of Z_L1 and Z_L2. How would you do so?
user avatar
0 votes
1 answer
93 views

Are impedance calculations only specific to sinusoidal inputs?

All impedance formulae we've derived in my course and calculations e.g. combined impedances in series have all assumed sinusoidal steady state. My question is, does the notion of "impedance" ...
user avatar
1 vote
1 answer
94 views

Building intuition on the behavior of inductors and capacitors with both voltage and current

I understand that an inductor cannot change current instantaneously, however I am not sure how that relates to the voltage. In a high pass RL circuit, for example, I know that the inductor presents a ...
user avatar
0 votes
2 answers
102 views

Current limiting rectifier with capacitive reactance (isolated)

[UPDATE] I have answered my own question with links to experimental data and theory. Please expand on that answer if you can for the reference of future readers. Thanks for replies so far and ongoing....
user avatar
0 votes
1 answer
56 views

Reactance to varying DC

Input signal (a) is AC. Input signal (b) is varying DC. As (b) has a frequency but does not change direction, does the capacitor's reactance have a different effect than input signal (a)?
user avatar
1 vote
4 answers
162 views

Keeping a cheap, DIY transformer safe

I want to design a cheap but safe, low-wattage, always-on heater to keep a small space above freezing. (A small underground tunnel that the water pipe for an automatic horse waterer goes through.) I'...
user avatar
  • 217
0 votes
1 answer
70 views

Effect of a capacitive or inductive divider on noise

I am used to thinking about the effect of an attenuator on a system's noise in the following way: there is some system noise (and signal) at the attenuator's input, coming from the preceding part of ...
user avatar
  • 41
0 votes
0 answers
47 views

What unit is expressing the effect of this capacitor in a common emitter amplifier?

I'm working through this handout I3.PDF in my attempt to understand negative feedback in amplifiers. The following formula appears, in which the author is substituting \$v_{out}\$ and \$v_{in}\$ to ...
user avatar
0 votes
3 answers
157 views

Why does impedance decrease in an MLCC as frequency increases?

I understand that the impedance of any capacitor decreases as frequency reaches the resonance frequency, following the formula Xc = 1 / ( 2 pi f C ), but why does the impedance of an MLCC such a ...
user avatar
3 votes
6 answers
1k views

Why does wire not have large capacitive reactance?

For capacitive reactance, I am presented this formula: $$X_C = -\frac{1}{2\pi fC} $$ Where clearly, the capacitive reactance is inversely proportional to the capacitance. This confuses me. We usually ...
user avatar
2 votes
0 answers
192 views

How do you calculate phase shift induced by a shunt capacitor?

Given a simple loaded-line shunt-capacitor phase shifter, how can I calculate the phase shift and insertion loss at S21 caused by the shunt capacitor (varicap in my case, but for any cap) assuming I ...
user avatar
  • 872
7 votes
2 answers
5k views

What is Negative Inductance?

I am experimenting with a stripline square spiral inductor in Sonnet and the graph is showing both a positive and negative inductance. What does it mean to have a negative inductance? Why does it ...
user avatar
  • 872
1 vote
4 answers
1k 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 ...
user avatar
0 votes
1 answer
50 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?
user avatar
0 votes
2 answers
57 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 ...
user avatar
  • 551
2 votes
2 answers
279 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\...
user avatar
  • 2,996
1 vote
1 answer
69 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.
user avatar
  • 57
0 votes
1 answer
49 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, ...
user avatar
  • 253
0 votes
1 answer
53 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 ...
user avatar
  • 1
0 votes
1 answer
324 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....
user avatar
1 vote
3 answers
188 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/...
user avatar
  • 11
0 votes
1 answer
110 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: ...
user avatar
1 vote
1 answer
291 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 ...
user avatar
  • 1,540
0 votes
0 answers
75 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: ...
user avatar
1 vote
3 answers
307 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). ...
user avatar
  • 77
0 votes
3 answers
300 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 ...
user avatar
  • 23
2 votes
2 answers
207 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 ...
user avatar
0 votes
2 answers
188 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 ...
user avatar
0 votes
0 answers
52 views

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 ...
user avatar
2 votes
1 answer
334 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 ...
user avatar
  • 151
1 vote
1 answer
1k 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 ...
user avatar
0 votes
3 answers
159 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 ...
user avatar
1 vote
1 answer
2k 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 ...
user avatar
  • 2,493
1 vote
2 answers
365 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 ...
user avatar
  • 289