Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

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. However, all the sources I found just state the…
Roo
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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 nonsense on this, is that just a fringe def, or…
Fizz
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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?
FISqrt
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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 swing above and below 0? What does it mean about the…
KJ7LNW
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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 energy usage meter by a fourth. He mentioned…
Everyone
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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 you do that, since(by definition, as it's is a communication line) you…
Tuomo
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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 the current rating (1.5A for example). However,…
DSWG
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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? UPDATE: Thanks for the great help. I choose Russel's…
HardQuestions
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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, but cost the power company plenty in terms of I2R…
STATER
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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 resistance function, and it gave me: 180 kΩ at 1…
endolith
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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 reactance is given by the equation: \$X_C\$ =1/( j…
nrnw
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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)? I forgot to add a parasitic resistor in series…
user1247
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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 will inductive reactance. Are there any other…
user167734
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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 and supply frequency, how is that related to the…
Ivan P.
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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. I gave it a try myself though, but I could not get…
MrMongoloid
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