I want to know if the following circuit is inductive or capacitive? What is the difference between inductive and capacitive?
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\$\begingroup\$ Inductive: the imaginary part of the full impedance is "positive" \$\endgroup\$– Antonio51Commented Feb 17, 2023 at 15:30
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1\$\begingroup\$ The impedance at the input to the circuit (where the voltage source connects) is net inductive with a little bit of resistance. \$\endgroup\$– Andy akaCommented Feb 17, 2023 at 15:41
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1\$\begingroup\$ From the perspective of the AC source, you can easily see that the capacitive reactance is very much larger than R2. So R2 dominates that parallel pair and you can ignore the capacitive reactance when answering the question. This leaves about 2 Ohms in series with the inductive reactance, which is by comparison 'large'. So it impedance is effectively just 2 Ohms in series with +j 600, or just 2+j600. The magnitude will be 600 and the argument (angle) will be about +89.8 degrees. Inductive, of course. \$\endgroup\$– periblepsisCommented Feb 17, 2023 at 19:34
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5 Answers
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Impedance determination of a circuit is a bit too broad. It requires a point of view. Most comments and answers chose the point of view of the source. Impedance can be expressed in rectangular form as:
$$Z=R+jX$$
or in polar form as:
$$Z=|Z|\angle\theta$$
If \$X\$ or \$\theta\$ is positive then the impedance is inductive. If negative then the impedance is capacitive. If \$X=0\$ or \$\theta=0\$ then the impedance is resistive.
answered Feb 17, 2023 at 16:51
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- Work with complex impedance rather than absolute value of reactance as you have now. So \$j600\Omega\$ for \$Z_L\$ and \$-j600\Omega\$ for \$Z_C\$
- Solve the circuit for the supply current.
- Check the phase difference between supply voltage and current. If current leads voltage, that's "capacitive". If current lags voltage, that's "inductive".
Alternate method: After switching to complex impedances, use circuit transforms to find the equivalent total impedance. Check the sign of its imaginary part.
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The difference between inductive and capacitive circuit is that in inductive circuits XL > XC and in capacitive circuits XC > XL. So, the circuit shown is inductive. In the circuit, XC in parallel with R2 results in an impedance Z2c. As (R2 << XC), we get Z2c ~ 1 ohm. Therefore, the total impedance Z of the circuit is close to XL ~ 600 ohms, inductive.
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\$\begingroup\$ what do you mean by Z2c? From where did you get that term? \$\endgroup\$– user220456Commented Feb 18, 2023 at 17:59
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\$\begingroup\$ I chose to perform a simplified analysis, which answers the question. Z2C is the name of the impedance of R2 parallel to the capacitive reactance of C. For simplicity, without performing complex analysis, then Z2C is approximately 1 Ohm. (0.999-0.001j). \$\endgroup\$– LuizzzCommented Feb 21, 2023 at 19:16
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Find the Thevenin equivalent impedance looking from voltage source. If the circuit has resulting impedance consisting of positive term as \$R + jX \$ ,the impedance is inductive or else it is capacitive. If the network is unknown, you can also try adding a large capacitor in parallel at the output or input. If the resulting impedance is capacitive which has the form \$R - jX \$ , the the network is capacitive or else it is inductive.
Capacitive or inductive nature of a circuit means that the equivalent impedance of the circuit is either capacitive or inductive.
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I want to know if the following circuit is inductive or capacitive.
Neither.
Do not assume that every circuit has to be one or the other. There are "1000" possible circuits, and, among them, only one is capacitive, only one is inductive. Your circuit is among the remaining "998" circuits.
A capacitive circuit is, for example, one that has a single passive component: a capacitor.
An inductive circuit is, for example, one that has a single passive component with a winding: an inductor, a motor, a relay coil, a transformer primary.
answered Feb 17, 2023 at 15:31
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3\$\begingroup\$ This is incorrect. The resistance in the capacitive branch dominates the capacitance. The inductance dominates the resistance in the inductive branch . So the impedance viewed by the source is not purely resistive :) \$\endgroup\$ Commented Feb 17, 2023 at 16:17
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1\$\begingroup\$ DID I say that it was "purely resistive"? Do not put words into my mouth. I said that it's neither capacitive nor inductive, which is 100% correct. I said that circuits don't have to be only one or only the other, that there are many other options, which is also 100 % correct. \$\endgroup\$ Commented Feb 17, 2023 at 19:58
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\$\begingroup\$ @DavideAndrea: You are 100% correct that not all circuits are resistive, capacitive, or inductive. Only linear circuits are. Unfortunately, you're trying to use that argument on a linear circuit, and it just doesn't work. Please note that OP's circuit is marked with reactances, so the analysis is already set for a specific frequency. \$\endgroup\$ Commented Feb 20, 2023 at 15:57
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\$\begingroup\$ @ Ben Voigt. Am I correct in understanding that you are stating that every linear circuit can be only one of three: options, resistive, capacitive or inductive? That there are no other possibilities? I dearly hope I misunderstood you. \$\endgroup\$ Commented Feb 20, 2023 at 23:21