What is Inductance: Definition and 494 Discussions

Inductance is the tendency of an electrical conductor to oppose a change in the electric current flowing through it. The flow of electric current creates a magnetic field around the conductor. The field strength depends on the magnitude of the current, and follows any changes in current. From Faraday's law of induction, any change in magnetic field through a circuit induces an electromotive force (EMF) (voltage) in the conductors, a process known as electromagnetic induction. This induced voltage created by the changing current has the effect of opposing the change in current. This is stated by Lenz's law, and the voltage is called back EMF.
Inductance is defined as the ratio of the induced voltage to the rate of change of current causing it. It is a proportionality factor that depends on the geometry of circuit conductors and the magnetic permeability of nearby materials. An electronic component designed to add inductance to a circuit is called an inductor. It typically consists of a coil or helix of wire.
The term inductance was coined by Oliver Heaviside in 1886. It is customary to use the symbol


{\displaystyle L}
for inductance, in honour of the physicist Heinrich Lenz. In the SI system, the unit of inductance is the henry (H), which is the amount of inductance that causes a voltage of one volt, when the current is changing at a rate of one ampere per second. It is named for Joseph Henry, who discovered inductance independently of Faraday.

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  1. dragonshadowbob

    Determining Inductance L in an LC Circuit

    Here is the circuit I'm working with. So, I was able to get the correct equation by using the Equation Omega=I max/Q max = 1/sqrt(LC). I calculated Qmax by multiplying 150V * .5microfarad, and Imax by doing the 40V/150Ohms. Then, I just solved for L and got the correct answer. My question is...
  2. M

    What factors determine the resistance and inductance in a coil?

    Hi what factors determine the resistance and inductance in a coil and they related i.e. if the resistance is high would the inductance be high ? Additionally, would the resistance and inductance value change over time? I only ask this as we tested the resistance and inductance on our coils...
  3. A

    I Mutual inductance in a transformer

    Hello! I have a question regarding the mutual inductance of two coils in a transformer. In the formulas for linked coils ##M=k*\sqrt{(L_1*L_2)}## where ##k=1## for a perfect coupling. I wanted to check my understanding about mutual inductance and see how it can be determined. When I vary the...
  4. Hak

    Inductance Puzzle involving coplanar conducting rings

    I solved the first point as ##L_n = \frac{\mu_0 n R}{2}##. How to proceed for the other point?
  5. E

    Is total flux linkage λ=dΨ*Ienclosed/I or λ=N*Ψ?

    In Sadiku, he used the formula dλ=dΨ * Ienclosed/I to determine the total flux linkage for coaxial cable for ρ<a and for a<ρ<b, but I applied this formula for the solenoid and it didn't work, the way that works for the solenoid is by using λ=N*Ψ. So why we multiply by Ienclosed/I in the coaxial...
  6. E

    I Is total flux linkage λ=dΨ*Ienclosed/I or λ=N*Ψ?

    In Sadiku, he used the formula dλ=dΨ * Ienclosed/I to determine the total flux linkage for coaxial cable for ρ<a and for a<ρ<b, but I applied this formula for the solenoid and it didn't work, the way that works for the solenoid is by using λ=N*Ψ. So why we multiply by Ienclosed/I in the coaxial...
  7. D

    Help with understanding of RF theory-Kinetic inductance parametric amp

    So this might be long question that requires some literature review but I will try condense it as much as possible such that hopefully I can get some help without the reader having to review the related paper. So I will start off by saying that I am involved in a honours thesis in which I need...

    Inductance in lightning protection

    A high frequency wire dipole antenna installed at 80 feet is fed with a balanced line, at the transmitter feed point is a 1:1 balun that the balanced feeline hooks to on one side, a tuner on the other. The 1:1 balun is 12 parallel turns of #12 around a ferrite core. The input to the balun has...
  9. W

    Parasitic Inductance, rough estimate -Single cable through steel

    DC case - but customer ran their cable run through a couple boxes, this would not be allowed in AC due to the eddy current created in fittings and the enclosure steel. ( I do not even know if code would allow this for DC) - but anyway. This is part of a high power dc system and I suspect the...
  10. E

    I Antenna inductance calculation (RFID applications, inductive coupling)

    Inductance of antenna coils of different shapes can be estimated. Some examples are: A circular coil with single turn. N turn multilayer circular coil. Spiral coil. N turn squae loop coil. etc. For plannar design (spiral, rectangular, etc) I have used this reference (from pag. 9 onwards)...
  11. J

    I How does a ferromagnet increase the inductance of an inductor?

    Inductance according to Faraday's law depends on a changing magnetic field. The magnitude of the induced emf depends on the magnitude of change in the magnetic field per change in time. Based on that, how does adding a constant magnetic field (a ferromagnet), increase the inductance of an inductor?
  12. J

    Find the inductance of an inductor in a circuit

    When the current has been running for a while we can treat the circuit connected to e like a battery with two resistors. The current at this point is 2.5 A so using kirchhoff's loop rule we find that the emf of the battery is 2V. $$\varepsilon - IR - IR = 0$$ When the switch flips to f, we can...
  13. warhammer

    I Guidance Requested on Inductance Formula for Solenoid

    In my textbook on EM, the formula for self inductance of a finite solenoid is given as: L= (μ(o)* N^2*A * {√(a^2+ l^2) - a} )/l^2 where a=Radius of each turn, l=length of solenoid. I am having trouble and extreme difficulty in trying to ascertain how this formula was derived in the book and...
  14. S

    Straight wire inductance vs wire radius

    I know that the whole topic of inductance in a straight wire is complicated (and has led to some heated discussions in this forum :smile:). I followed Rosa's derivation and can see that it leads to an inverse relation of the inductance to the wire radius, and from what could understand, the...
  15. C

    I Preventing parasitics for wires?

    This is related to a question that I asked here: https://physics.stackexchange.com/questions/650709/one-way-magnetic-shielding. Please take a look at the check-marked answer. There is a material that can act as a one-way magnetic/electric shield. My question is if this material were to be used...
  16. D

    Inductance of Parallel Coils on an uncut toroid magnetic core

    Hi, I have a toroid of a soft magnetic material (any). I wind the complete toroid with single turn coils and connect all their terminals in parallel. Then I wind a second layer of single turn coils on the previous layer and so on. I want to calculate the equivalent inductance L. I calculate it...
  17. Jason-Li

    Engineering Mutual Inductance between two conductors

    Hello hope everyone at PF are keeping well! Looking at this problem but don't know if I have oversimplified it and my final answer doesn't seem right? So I drew the equivalent circuit: Then went onto calculate: I1 = 1/(R1+RL1) = 0.01A ω = 2πf = 2π*109 rads-1 so then with Vi being the inducted...
  18. Ntip

    Finding Inductance and Mutual Inductance

    I am trying to solve for inductance through FEA simulation. I and doing eddy current simulations so I can have H field, B field, and current density available. I am also trying to find an equation for the equivalent inductance with multiple conductors. I know that for two conductors it is Leq...
  19. dlang99099

    Relating Maxwell's equations to parasitic inductance due to layout

    I am trying to show how parasitic inductance is increased or decreased based on coupling between adjacent parallel capacitors. These capacitors are DC link capacitors so I'm not sure if that means it is not time varying and maxwells equations is no longer relevant?
  20. E

    Finding the inductance of a rotating cylinder shell

    First, the correct answer is μ0*π*R^2. I tried to look at the cylinder like it was a solenoid, this technique was used in my class. Then I tried to find the current of the solenoid, to do that I looked at a piece of a solenoid with a legnth of dz, then: I=dq/dt=(2πRσ*dz)/(2π/ω)=ω*R*σ*dz. The...
  21. P

    Clarification about Mutual Inductance

    emf = ##\frac {-N_{2} {d\phi}_{B2}} {dt}## ## M_{21} = \frac {{N_2}{\phi}_{B2}} {i_1}## are the equations This is the original position, now the coil 2 is moved so the axis is perpendicular. The flux ##{\phi}_{B2}## due to i1 is the amount of flux cutting the coil 2 due to change in current...
  22. cianfa72

    Accounting for mutual inductance in a Hartley Oscillator

    Hi, I'm watching a video about Hartley oscillator and I'm in trouble with a simple assumption: as stated at minute 5:50 if the two coils ##L_1## and ##L_2## are wound on the same core then taking into account the mutual inductance M he gets: ##L^ {'} _1 = L_1 + M## ##L^ {'} _2 = L_2 + M##...
  23. johnboyman

    Problems figuring out this inductance formula

    Hello. I am working this formula. I= 1/L∫Vdt . The following website have the best explanation of it. http://www.learningaboutelectronics.com/Articles/Inductor-current-calculator.php I am confused with a few things about it. One is that this website says If the current is Ac then the value...
  24. harsh22902

    Mutual Inductance between a coil and a long straight wire

    In the given question they have not provided the dimensions of the coil so I assumed it to be very close to the wire and having negligible dimensions compared to the wire . Then EMF induced in the coil due to the current in the wire comes out as M*a . Which when divided by resistance gives...
  25. mcastillo356

    Why does current need to vary in an inductor?

    In a power transformer, the variation of the current in one circuit induces a current in the other. This cause-effect relationship is two ways. If circuit A affects circuit B, then B circuit will affect A circuit; this is the cause of the concept of mutual inductance. However, it's not necessary...
  26. E

    Need help with a parallel inductance calculation for this transformer

    I have a transformer with the primary winding connected to a 115 volts 60Hz supply, the current is 0.230 amps AC, with a resistance of 25.3 ohms. The secondary winding is connected to an inductive load. The voltage across the secondary winding when the load is connected is 13.14 voltage AC with...
  27. A

    Inductance and Charge Redistribution

    I tried applying loop law but I am not really sure we don't really have a closed loop here. I guess they're testing some concept here that I'm not very good at (Why do i keep coming back to mutual inductance for some reason:|) Any help will be appreciated:)
  28. Indula

    How to calculate the inductance of a center tapped solenoid ?

    I'm trying to drive a transformer using a ZVS power supply. The primary coil that we use here has to be wound center tapped. The output frequency depends on the inductance of the primary winding and capacitance used in the circuit. The circuit of a ZVS power supply is as follows, The...
  29. M

    What is the Relative Permeability of Iron in a Solenoid?

    So the equation is L=μoμrN^2A/l I am wanting to make μr the subject and I think this is how i do it? μr = L*l/μoN^2A However when I type in this equation i am expecting to get about 200 for the relative permeability of iron. However, i am getting like 9x10-3 which is nowhere near 200. For...
  30. D

    Voltage and current as functions of time for a series RL circuit

    I already found ##I(t)## using Kirchhoff's laws, I got the equation ##V-RI-L\frac{dI}{dt}=0\Rightarrow L\frac{dI}{dt}=V-RI## then I solved the differential equation getting ##I(t)=\frac{V}{R}\left[1-e^{-\frac{R}{L}t}\right]##. My problem is founding the voltage as a function of time ##V(t)##, I...
  31. peace

    Mutual inductance between a very long, straight wire and a Semicircular loop

    I think I have to assume a point like P in the semicircle. The point in terms of r and θ: P (r,θ). So the magnetic field at that point: B = µI/2π(R+rcosθ) . So the magnetic flux: Φ = ∫B.dA= µI/2π ∫∫ rdrdθ / R+rcosθ . Is this the correct solution?
  32. R

    A problem in mutual inductance

    I have gotten my average induced emf to be 96 x 10^-3V using the formula, e=Nx(∆I)/t but the problem lies in calculating the inductances.
  33. T

    Inductance of a Solenoid with a Core inside

    For finding magnetic field ##B##, We see this question like two Solenoids. for the first one, we have ##\int B ds = \mu I## so ##B x_0 = \mu I n x_0 ## so ##B = \mu n I##. For the second one we have ##B = \mu_0 n I##. For the Inductance we have ##L = \mu l n^2 A## so we have ##L_1 = \mu x_0...
  34. D

    I Electromagnetic Fields and the manipulation of Space-Time

    Summary: Mathematical and Physical queries in regards to Electromagnetic Fields and their manipulation of Space-Time. I recently started looking into Einstein's Field Equations, to get a better understanding of how mass distorts and curves the plane of Space-Time, however from doing this I...
  35. D

    Mutal inductance depending on current

    My frient had an experiment in lab. They measured the mutal inductance on two coils wraped around one feromagnetic core. When the current of the first coil was 1, 2, 3, 4, 5 mA the mutal inductance was 94 mH. Then they were told to rise the current to 10 mA, the mutal inductance went to 160 mH...
  36. M

    Does Mutual Inductance Affect Voltage in an Open Circuit?

    Hi, so my question is basically: Does the mutual inductance from coil 1 show up in the voltage of coil 2 even if coil 2 is an open circuit? I would think that the answer is yes, as the Mutual inductance depends on the current passing through coil 1? However, the answer scheme seems to ignore...
  37. J

    How do you calculate the inductance of a metal sphere with electrical contacts?

    Hey everyone this is my first thread i was wondering how you calculate the inductance of a solid sphere. Say a sphere for example of 5cm diameter with electrical contacts on opposing sides 0.5 cm in diameter. Any help would be much appreciated
  38. Adesh

    How to solve a complex equation to get the current?

    I was reading The Feynman Lectures on physics http://www.feynmanlectures.caltech.edu/I_23.html chapter 23, section 4. In it he derives the equation for current when inductor, resistor and capacitor is connected in series with an alternating voltage source, he derives this equation:-...
  39. T

    Calculate the inductance of a solenóide wound on an iron core

    Hello friends of the forum! I'm here with a doubt! I have a solenoid of cross-sectional area 5cm and length 9cm with iron core of relative permeability (ur) 9,000, I wonder how to calculate this silenoid!
  40. O

    Johnson-Nyquist noise of an inductor

    Homework Statement Although it's easy to find calculations of thermal noise for resistors and capacitors, the equivalent for inductors is not found. What is the relevant formula? Is there some simple conversion for this? Homework EquationsThe Attempt at a Solution
  41. DaTario

    Detailed derivation of the inductance effect

    Hi All, Is there any reference that shows in detail how to deduce the inductance effect of a coiled wire, starting from the magnetic influence of each current element ##i\, ds## on the others? Best wishes, DaTario
  42. G

    Dot convention inductors in series: equation confusion

    Homework Statement So I'm really confused with mutual inductors and dot convention. If your answer is going to be a link to any website I can assure you I read them all and that only left me more confused. So here are my questions: Homework Equations 3. The Attempt at a Solution [/B] ->...
  43. G

    Mutual inductance coefficient with so little info

    Homework Statement I have the following circuit: The two inductors are connected in series are characterized by internal resistances R1 and R2 and self-inductances L11 and L22. The magnetic coupling factor between the inductors is k = 0.75. The inductors carry the same current i. What is the...
  44. Marcin H

    Inductance of two-conductor line - Proof Questions

    I am trying to understand how to derive equations for the inductance of an x-conductor line. Any number really. But I want to understand the proof for a two-conductor line first. So to start any of these proofs you first need the equation for the per unit length inductance: I know R is...
  45. D

    Ratio of Inductance between 2 Solenoids?

    Homework Statement [/B] 1. Two solenoids, A and B, are wound using equal lengths of the same kind of wire. The length of the axis of each solenoid is large compared with its diameter. The axial length of A is twice as large as that of B, and A has twice as many turns as B. What is the...
  46. J

    Comparing self inductance of three solenoids

    Homework Statement Homework EquationsThe Attempt at a Solution Self inductance depends on the geometry of the solenoid . It doesn't depend on the sense of windings . So , L1 = L2 . But I don't understand how to deal with superconducting wires . Does a superconducting wire affect the...
  47. J

    What does self induction per unit length signify?

    Homework Statement Homework EquationsThe Attempt at a Solution Self inductance L = μ0n2πr2l . This means it depends only on geometrical factors . So , self inductance in both the cases should be equal . But if I think in terms of L = Φ/I , then Magnetic field at the center is twice that...
  48. Who Am I

    Inductance of a Solenoid Around a Conducting Sphere?

    I got into a little debate about the nature of a problem where you put a giant solenoid around the equator of Mars to give it a magnetic field (not my idea, I like futuristic things but... there are probably better things to worry about). Anyways, I got into a debate about the effect of the...
  49. Ron Burgundypants

    Altered inductance around a solenoid in a cryostat (from Eddy currents?)

    I'm trying to use a solenoid to measure the magnetocaloric effect of dysprosium. The effect is highest at the Neel temp which is down near 180K. I have a solenoid in a cryostat to get the correct temperature. The cryostat's heat exchanger is made of a thick copper cylinder and I think it is...