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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Why does voltage always lead current by 90 degrees in an inductor?
I have learnt that in an inductor voltage leads current by 90 degrees. However, I do not fully understand why it is 90 degrees.
I have been looking everywhere for more information on why this is so. ...
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Is capacitor reactance [sometimes] defined with negative sign?
Wikipedia currently claims so
but I've looked in 6 books via Google Books and it's not defined like that, i.e. it's just
$$ X_c = \frac{1}{\omega C} = \frac{1}{2\pi f C} $$
Is Wikipedia full of ...
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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?
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If the energy meter sees a reactive load, will it register a lower reading?
At an exhibition on home appliances, I saw this guy hawking his 'energy saver device'. The guy claimed that merely plugging his instrument into the supply would reduce the consumption reported in an ...
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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 ...
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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 ...
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Sensing AC high voltage to microcontroller
I'd like to sense if I have AC 220V 50HZ available, and convert it to some logical level.
I made such circuit, will it work?
I use C1 as a resistor.
Any recommendations what can be improved?
...
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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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How do reactive currents cause power transfer?
I read in 'The Art of Electronics':
Power factor is a serious matter in large-scale electrical power distribution, because reactive currents don't result in useful power being delivered to the load,...
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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 ...
user167734
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Why doesn't LCR meter measure expected reactance?
Measuring an unknown capacitor with a Tenma 72-960 LCR meter, I got 89 nF at both 1 kHz and 120 Hz, which I believe because I measured other known capacitors, too. Then I tried measuring with the ...
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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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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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How to calculate reactance of a capacitor for a square wave
Capacitors block DC signals and pass AC signals. Their resistance, ideally, is purely reactive (no real part to its impedance). For a sine wave of frequency f passing through a capacitor, the ...
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Solving the second-order differential equation for an RLC circuit using Laplace Transform
I'm trying to solve this second order differential equation for a RLC series circuit using Laplace Transform. The Laplace transform of the equation is as follows:
$$I(s) = \frac{E}{s^2+ \frac{R}{L}s +...
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Inductor value given in OHM/Amp
I've been trying to figure out the inductance in Henries from a schematic of a Rabbit Microprocessor development board, however, instead of finding an inductance value over the components in question, ...
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Why does an induction motor draw more current when the load is increased?
I am aware that a coil has inductive reactance when powered by AC besides the еlectrical resistance which is typically very low.
Considering the fact that reactance is proprotional to the inductance ...
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Understanding Lead in a causal system
I've gone through school and done all the work but looking back at it i still don't quite get it.
The rule is current in a capacitor leads and in an inductor lags. The inductor makes perfect sense ...
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Inductive reactance: frequency vs current. Why current goes to zero as frequency increases?
Suppose I have the circuit below with the frequency of the voltage source as a free parameter. Assuming the inductance is constant, the current flowing through the circuit shoud equal
$$I(f) = \frac{...
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How can the infinite reactance of either primary or secondary in an ideal transformer draw current?
Assumption 1:
An "ideal" transformer is said to have very large primary, secondary, and mutual reactance.. (self-inductance/mutual-inductance tending toward infinity), has a unity coupling coefficient ...
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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 ...
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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 ...
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How do I derive capacitive reactance formula from Cdv/dt?
I know that capacitors block DC and low-frequency AC, and their reactance decreases as the frequency of the AC circuit increases. As such they are useful as high-pass filters and so forth.
I had ...
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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 ...
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At what frequency will the reactance of a 1μF capacitor equal to the resistance of a 2kΩ resistor?
Here is my work:
\$ R = 2000 \Omega\$
\$ X_L = 2 \pi f L = 2 \pi (1 \mu F) f = 6.28\mu F(f)\$
\$f = \dfrac{2000 \Omega}{6.28 \mu F} = 318.471MHz \$
Does this look right to everyone?
user22490
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Why is it impossible to realize elliptic even-order filters with \$R_S = R_L \$?
Referring to RLC continuous-time prototypes of filters, I have read that an elliptic filter of even order can not have equal source and load termination resistances.
The trasfer function for such ...
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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° ...
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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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Excessive temperature on cheap soldering iron - will series capacitor fix it?
Soldering iron came in a $14 USD kit off eBay. Lots of neat stuff, but the iron became so hot as to badly damage a DIY Kit. After a 2nd chance w/ the same results, it was hacked, Heating element of ...
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Why do inductive and capacitive reactances have opposite signs and why don't they cancel out each other?
For example, in a series RLC circuit with an AC source why is total reactance inductive reactance minus capacitive reactance? I don't need any mathematical proof. What is a logical answer for that?
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Where does j come from in the reactance of L and C components?
So the reactance of the inductor is jωL while that of capacitor is 1/jωC. My question is that starting from the differential equations that describe the dynamic behavior of these circuit components, ...
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High frequency rf resistors
I need non reactive resistors for use at LF thru HF (100KHz thru 30MHz) for use with radio receiving antennas as terminations. Carbon comp and carbon film work but have their shortcomings in stability ...
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Power calculation and Ohm's Law for Reactance
Hi I have the following question:
V = 120V,
I = 10 A, I lags V by 60degrees
simulate this circuit – Schematic created using CircuitLab
The load consists of a resistor and an inductor in ...
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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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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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AC analysis: finding L and R
EDIT: there should be arg[I2] instead of arg[I3]
I've tried to replace V1, C1, R1 with Thevenin equivalent, but I've lost in my calculations. Is there any better approach?
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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 ...
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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 ...
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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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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 ...
user126396
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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 ...
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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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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/...
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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'...
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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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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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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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Why is the Inductive reactance formula (XL=2πfL) not working for me?
I have an inductor labeled as "222" which I believe its means that its inductance value is equal to 2200 Microhenries. I double checked by measuring the inductor with and LCR meter and the value ...
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Formulae for induced back-EMF
I'm doing AC theory, and I'm looking for different formula to find induced back-EMF. Given inductance, voltage, current, frequency, I'm able to find inductive reactance, current and voltage on each ...
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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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