# Impedance Definition and 42 Discussions

In electrical engineering, electrical impedance is the measure of the opposition that a circuit presents to a current when a voltage is applied.
Quantitatively, the impedance of a two-terminal circuit element is the ratio of the complex representation of the sinusoidal voltage between its terminals, to the complex representation of the current flowing through it. In general, it depends upon the frequency of the sinusoidal voltage.
Impedance extends the concept of resistance to alternating current (AC) circuits, and possesses both magnitude and phase, unlike resistance, which has only magnitude.
Impedance is a complex number, with the same units as resistance, for which the SI unit is the ohm (Ω).
Its symbol is usually Z, and it may be represented by writing its magnitude and phase in the polar form |Z|∠θ. However, cartesian complex number representation is often more powerful for circuit analysis purposes.
The notion of impedance is useful for performing AC analysis of electrical networks, because it allows relating sinusoidal voltages and currents by a simple linear law.
In multiple port networks, the two-terminal definition of impedance is inadequate, but the complex voltages at the ports and the currents flowing through them are still linearly related by the impedance matrix.The reciprocal of impedance is admittance, whose SI unit is the siemens, formerly called mho.
Instruments used to measure the electrical impedance are called impedance analyzers.

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1. ### Total (net) reflection of a wave moving through 3 different impedance regions

I know for a wave moving from left to right, ##\psi_i = Ae^{i(\omega t - k_1x)}## The first reflection where ##Z_1## is ## R_{12}Ae^{i(\omega t - k_1x)}## The second reflection. The wave moves from 2 to the limit between 2 and 3 then reflect... Thus, ##T_{12}R_{23}T_{21} Ae^{i(\omega t - k_1 x...
2. ### Engineering Analyzing the output impedance and open loop gain of a IC-741 Op-Amp

Here is the internal circuit of the 741 Op-Amp - Looking at the output stage, the output impedance seems to be the series combination of ##25 \Omega## and ##50 \Omega##, that is ##75 \Omega##. Is this a qualitative explanation enough to justify the output impedance, or am I wrong somewhere and...
3. ### Engineering Resonance in AC circuits

Here's my attempt at a solution.
4. ### How do you calculate the impedance of the primary circuit?

I'm not sure if it helps for what I'm looking, but I've calculated the mutual inductance, M, using the equation: M=U2/(ω*I1) = 106.3μH. I don't need the numerical value in particular, I just want to find a way to deduce the formula in order to calculate Z1. Thank you!
5. ### Max velocity of a vibrating loud speaker membrane given sound intensity

My attempt: p and T allows us to calculate ##Z=402 \frac{kg}{sm^2}## using ## Z=p*\sqrt(\frac{\gamma*M}{R*T})## . The sound intensity level at 10 meters allows us to calculate the intensity at 10 meters to be I=10^{-7} W/m^2 using ##50 = 10*log(I/I_0)##. Then, using the formula...
6. ### Engineering Circuit input impedance with ground in an OP Amp circuit

I've been given the following circuit and have been asked to find the input impedance and the impedance between the input terminal and ground. I've never encountered an operational amplifier configured like this. I know that the voltages at the - and + terminals of the op amp are ideally equal...
7. ### Impedance of RF Connectors

I am just a bit confused as to how impedance is matched with RF connectors such as type-N or BNC connectors. I know Coaxial cabling and RF connectors come in common impedance ratings like 50 or 75 ohm but how is this all matched properly? For example many people have told me that when using...
8. ### I The role of capillaries in a dilution refrigerator

I've been trying to understand how dilution refrigerators work and inbetween intermediate steps, between different temperature points, I see capillaries here and there under the name of impedances. After some googling, I somewhat convinced myself that it's to build up pressure before and after...

Hi all, I am currently working on a project where the output/load consists of both a variable inductance and variable resistance, whilst the circuit driving this load is a class E radio frequency (RF) power amplifier with low resistance but relatively high/medium reactance (attempting to design...
10. ### I Effect of impedance changes less than a wavelength

I am interested to know what is the impact of various length scales of impedance changes on wave propagation. From undergraduate physics (a few years ago for me) I roughly remember how to derive reflection and transmission coefficients for a wave travelling from one medium to another with a...
11. ### Input impedance of a "Ladder" transmission line

Homework Statement My electronics&physics lecture notes contain the following side note: ___ "A ladder transmission line comprises an alternating sequence of segments of two different transmission lines both of length $l$ with characteristic impedance $Z1$ and $Z2$. If the line is constructed...
12. ### I Short Circuiting the Secondary of a Transformer/Self Impedence

Thank you for reading my post. I was watching the video this video on transformers and saw an amazing demo: From 4:00-5:20 the guy does an experiment where he has a simple transformer circuit set up: On the primary side of the transformer he has an AC power supply, and a lightbulb. On the...
13. ### Wall thickness vs frequency... sound isolation

When sound hits a wall,part of it gets reflected and part of it gets transmitted due to acoustic impedance difference between solid and air. My problem,and point of this question is that having material or gas impedance number is completly useless unless we know the frequency and wall...
14. ### Stray/Parasitic Capacitance - Impacts phase velocity?

Hey everyone, I'm trying to measure the stray capacitance in a circuit comprised of an rf signal generator, an oscilloscope, a coaxial cable (short-circuited) and some capacitors. I measured the resonant frequencies of the coaxil cable for varying values of capacity (0pF to 850pF) between 4MHz...
15. ### Acoustic impedance in Materials

Acoustic impedance of material is defined by density multiply by the velocity of waves within the base material. My question is if i have a tubular or hollow part with a base material, does this count as a reduction of density compared to the base material of the tube or hollow part. Would the...
16. ### Why does having a high input impedance and low output impeda

Homework Statement Say you connect Circuit A with low output impedance to circuit B with high input impedance. Why does this cause minimal voltage drop compared to connecting them the other way around (high output to low input). Homework Equations P = V^2/R P = IV The Attempt at a Solution I...
17. ### How should I calculate conductivity

Hello, I would like to ask if I have this data from impedance spectroscopy: frequency, Z(im), Z(Real), how should I calculate conductivity ? Should I use R(im) or R(re)?
18. ### Engineering Finding Phase Difference in an RC circuit

Homework Statement Homework Equations ##V = ZI## ##Z_R = R## ##Z_C = -\frac{j}{\omega C}## ##Z = \sqrt{R^2 + (\frac{1}{\omega C})^2}## ##P_{av} = \frac{1}{2}V_m I_m cos(\phi)## ##\phi = arctan(\frac{-1/\omega C}{R})## ##\Delta \phi = \phi _1 -\phi _2## The Attempt at a Solution I've found...
19. ### Engineering RL Circuit Power Computation

I'm having some problems understanding why my computation deviates from solutions. I thank in advance to anyone who can give me some tips where I've gone wrong. Homework Statement Compute real power on resistors ## R_1 ## and ## R_2 ## and reactive power on inductor ## L ##. Circuit is powered...
20. ### Is there microscopic version of general Ohm's law of V=IZ?

Hello. Resistive Ohm's law is famously known as V = IR. We can derive its microscopic version as being followed. V = El, where E and l are, respectively, an electric field and a resistive load length over which a voltage drop V is developed. I = JS, J and S are a current density and a...
21. ### Current and voltage with inductors and capacitors

Homework Statement I am given the following circuit: and asked to solve for v(t) and i(t) Homework Equations The Attempt at a Solution If this is right, I don't know where to go from here.
22. ### RMS Current through RLC combination ciruit

Homework Statement Referencing the attached picture: a) Show that the RMS current in the 1 kΩ resistor is 6.5mA. b) If the AC voltage source was replaced by a battery, what would the current in the resistor be? Homework Equations V = IR Z = √(R^2 + X^2) The Attempt at a Solution To begin, I...
23. ### Combine capacitors and inductors to be frequency independent

Is it possible to combine (possibly infinite) capacitors and inductors to get a total impedance which is independent of frequency. If so, how?
24. ### Modeling and Measuring an Electromagnetic Coil in ANSYS HFSS

I've been attempting to model a simple electromagnetic coil using HFSS, and have so far been unsuccessful. I have no problems constructing the coil; this is a simple geometry problem. I have a wire of a known geometry with insulation surrounding the wire, then a construct a helical path and then...
25. ### Discrete Differential Amplifier

Homework Statement Calculating the open loop output Impedance at 1kHz and the open loop differential gain The Attempt at a Solution Here is the approach. INPUT STAGE: Q111 and Q112 Av1 = Rtot/2re, where Rtot is the total resistance of R117 and the input resistance of Q78 which is Rin. So...
26. ### The battery equivalent internal impedance equation

Homework Statement Hello, long story short: I need to create a model of Li-Ion battery and i'm stuck on calculating the battery equivalent internal impedance. The thing is, I don't know the equation or even how to make one. However, I have a circuit drawing: Homework Equations Values in...
27. ### Impedance of a 5kW generator (synchronous single phase)

Hi everyone! As a Belgian student electrical engineering, I am going to Peru this summer with Humasol vzw, a development organisation that works with engineering students. Our job is to build a hydro turbine next to a small river to provide a little community with electricity. Also part of our...
28. ### Solving voltage divider involving capacitors

Homework Statement Given ZV1 = ZV2 = 100Ω, ZCCV = ZCV = 2000/j = -2000j, and VV/VC = 0.04789. I'm trying to get the given VV/VC result. Homework Equations I know that 1/ZV = 1/ZV1 + 1/ZV2 + 1/ZCV VV = ZV / (ZV + ZCCV) * VC The Attempt at a Solution 1/ZV = 1/ZV1 + 1/ZV2 + 1/ZCV = 1/100 +...
29. ### Impedance of capacitor and inductors

I do not understand how to solve capacitors and inductors with impedance. I do not even know what it is that they use it to solve for. My understanding is that the define the source as a sinusoid using the complex exponential form, and that all voltages and amperage are now also complex...
30. ### CMOS to Microstrip Impedance Matching

I need to somehow take the output of a CMOS IC and transmit that signal over a 50 Ohm Microstrip line. The output impedance of the CMOS IC is about 15 megaohms. I see a lot of examples for going from 75 ohms to 50 ohms or similar but nothing on something of this magnitude. Any ideas? CMOS...
31. ### Engineering RLC Circuit

The question is: The voltage source in the above circuit is a sinusoidal AC source with constant amplitude and constant phase shift but an adjustable frequency. Calculate the frequency ω at which the phasor current I...
32. ### Double check apparent power definition

Hey just to make sure, can we say apparent power S = V^2 / Z for a complex impedance Z? And do we have to worry about conjugates at all? Cheers
33. ### Earthing and Grounding or Protective Earthing

1 “earthing” for bonding of equipment and circuits to common plant earth electrode potential, 2 “protective earthing (PE)” when this bonding is required for personal safety provisions 3 “grounding” for interference suppressing bonding of screens, sys- tems with ground level 4. low-impedance...
34. ### Engineering Calculating values of impedance in a series/parallel circuit

Homework Statement Hello everyone, I have recently come under some stress from not being able to get these answers correct. I need to calculate these values: Zeq IT XL2 XL1 VR1 VR2 VL1 VL2 For this series circuit: And these values: Zeq IT XL2 XL1 IR1 IR2 IL1 IL2 For this parallel...
35. ### Engineering Instantaneous Current in single phase circuit

Homework Statement SOURCE: v(t) = (311)cos(314t) [v] IN SERIES WITH: R = (0.3) [Ω] L = j(0.7) [Ω] "load" = 2.5 + j(1.0) [Ω] Homework Equations Find the instantaneous current, and the phasor current. The Attempt at a Solution (1.) I first found the frequency of the source: (314) / (2*pi) ≈...
36. ### Impedance and EMI/RFI

Question in relation to audio. I read online that a low impedance system is less susceptible to EMI and RFI than high impedance. How? I thought that high impedance = high resistance, therefore higher resistance to EMI and RFI. Would love to be updated with the explanation. Thanks.
37. ### Question about transformer reflected source

The following show the idea how a Thevenin equivalent source is used to replace the primary circuit of transformer. https://www.dropbox.com/s/0kaazx1d1srgirz/reflectedsource.jpg?dl=0 https://www.dropbox.com/s/0kaazx1d1srgirz/reflectedsource.jpg?dl=0 In textbook it is commonly stated that the...
38. ### Complex reflection and transmission coefficient of EM waves

I have a question about complex reflection and transmission coefficients. For example, I am modeling a wave in air (medium 1) ## \varepsilon = \varepsilon_0 ## reflecting on, and transmitted to, a medium 2 with ## \varepsilon = \varepsilon' -j \varepsilon'' ## If the wave would have...
39. ### Engineering Finding current/impedance in circuit

Homework Statement Homework Equations Law of Superposition I=V/R The Attempt at a Solution I am reducing the circuit. i) By law of Superposition, short circuit V2 100 ohms on the leftmost branch and 50 ohms on the rightmost branch, both are in parallel so 100*80/(100+80)=44.4 ohms seen by...
40. ### Electrical Impedance

i am a 3rd year Mech batch doing my dissertation on developing an inductive sensor to determine wear in brake discs. As you know it works by inducing eddy currents into the disc and the are monitored by measuring the impedance of the coil. i am really struggling with understanding the impedance...
41. ### Ideal Transformers and finding the steady state current?

Homework Statement In the circuit shown the 120V, 60Hz source supplies the ideal load shown through an ideal 2:1 transformer. What steady state current would you expect to read on the rms ammeter shown (please find the picture attached)? Homework Equations Zeq = (1/Z1+ 1/Z2)^-1 Z1 =...
42. ### Quick question, phasors and impedance

Please see attached On line S=0.5*V*I why is the minus sign removed from in front of the "I" angle. 25.38 specifically. Could is be a typo? http://imgur.com/eUmEovo