What is Inductor: Definition and 454 Discussions

An inductor, also called a coil, choke, or reactor, is a passive two-terminal electrical component that stores energy in a magnetic field when electric current flows through it. An inductor typically consists of an insulated wire wound into a coil.
When the current flowing through the coil changes, the time-varying magnetic field induces an electromotive force (e.m.f.) (voltage) in the conductor, described by Faraday's law of induction. According to Lenz's law, the induced voltage has a polarity (direction) which opposes the change in current that created it. As a result, inductors oppose any changes in current through them.
An inductor is characterized by its inductance, which is the ratio of the voltage to the rate of change of current. In the International System of Units (SI), the unit of inductance is the henry (H) named for 19th century American scientist Joseph Henry. In the measurement of magnetic circuits, it is equivalent to weber/ampere. Inductors have values that typically range from 1 µH (10−6 H) to 20 H. Many inductors have a magnetic core made of iron or ferrite inside the coil, which serves to increase the magnetic field and thus the inductance. Along with capacitors and resistors, inductors are one of the three passive linear circuit elements that make up electronic circuits. Inductors are widely used in alternating current (AC) electronic equipment, particularly in radio equipment. They are used to block AC while allowing DC to pass; inductors designed for this purpose are called chokes. They are also used in electronic filters to separate signals of different frequencies, and in combination with capacitors to make tuned circuits, used to tune radio and TV receivers.

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  1. 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
  2. Lapse

    Engineering Finals Study Time A Two Source Circuit w/Inductor, Cap, and Resistor

    Homework Statement Homework Equations Z = √(XC2 + XL2) XL = 2πƒL XC = 1 / 2πƒC I = V/Z The Attempt at a Solution First off, thank you for all of the help this semester. I'm sure you'll be seeing questions from me in the spring also. Here is how I'm thinking about this problem: 1. Using the...
  3. R

    Work Done on Charges by a Capacitor and an Inductor

    Homework Statement https://imgur.com/vQRoMjZ Homework EquationsThe Attempt at a Solution I believe that the inductor does negative work on the charges via the electric field (by way of induced EMF). I am unsure about how the capacitor would be doing positive work, though. Can anyone help steer...
  4. Lapse

    Current Through an Inductor at time t

    Homework Statement Homework Equations [/B] V = 1/L di/dt I = Io x (1 - e^(-t/L/R) Tau = L/RThe Attempt at a Solution [/B] Ii = 0mA ; If = 1mA Vi = 1V ; Vf = 0V Tau = 15uH / 1k Ohms = 10ns If my above is correct, then voltage and current equations through inductor should be as follows...
  5. Lapse

    Integral for Current through an Inductor -- Not Working

    Homework Statement [/B] Calculate, and plot along with (on the same plot) the voltage seen below, the current flowing in the following circuit using the integral relationship between the voltage across an inductor and the current through the inductor. Verify your hand calculations and plot...
  6. AchillesWrathfulLove

    What is the purpose of an inductor?

    If an inductor requires a changing current to produce a voltage drop across itself Then is there any purpose to an inductor with constant current going through it? Is AC usually used with inductors since its always changing.
  7. M

    How to find the expression for current and power in an inductor

    Homework Statement A voltage of V = V_0 sin(\omega t) is applied to an inductor. Find an expression for the current and hence the power. Homework Equations I have used the equation: V = -L \frac{di}{dt} and for power: P = IV The Attempt at a Solution I tried to find I(t) by integrating...
  8. A

    Questions about how an inductor works

    Hi all I am confused with the inductor working, I want to understand it in very much detail. Pl see the following image, First Thing : Here we have an initially uncharged inductor L in fig 1 with a switch S and a const. voltage source of voltage V. Now in fig 2 let the switch is closed at...
  9. prodo123

    Time required store half the maximum energy in an inductor

    Homework Statement A 35.0 V battery with negligible internal resistance, a 50 Ω resistor and a 1.25 mH inductor forms a RL circuit. How long will it take for the energy stored in the inductor to reach one-half of its maximum value? Homework Equations ##i(t)=I_0 e^{\frac{-tR}{L}}##...
  10. A

    Engineering Confusing circuit analysis question

    Hi I have the following situation: (Please see attached pic) I want to know if equation (4) i have written is correct. What is confusing me is that, I remember being told in circuit analysis that each energy storage element should have its own state variable. But in this situation when I...
  11. K

    An inductor and a capacitor with a state

    Hi. Is it correct to say that an inductor with a state, that is some level of current inside it, and a capacitor with some voltage, are equivalent to a current source (in the case of an inductor) and a voltage source (in the case of a charged capacitor) respectively at that instant of time? Of...
  12. R

    Battery connected to a pure inductor with a Zero-resistance wire

    I know the mechanism of a circuit containing just a capacitor connected to battery in resistance less wire. The particles are just tending towards making same emf on capacitor. But, I am not able to think clearly for the case of inductor. As, we connect battery and as resistance is 0.So,current...
  13. A

    Equations for three inductors connected together

    I have a system with three inductors connected together at a common point. The unconnected ends of each inductor is connected to an independent voltage source. Basically I want to get three expressions for the dynamics of the currents with V1, V2 and V3 as inputs. i.e. i need to eliminate the...
  14. A

    Treating an inductor as a current source?

    https://imgur.com/a/Yb2vpmp why can the inductor be treated as a 1A source?
  15. R

    What is the maximum value of the current through the inductor?

    1. Homework Statement : Two identical uncharged capacitors A and B each of capacitance C and an inductor L are arranged as shown in the adjacent figure. At t=0, the switch S1 is closed while switch S2 remains open.At time t=to=√(LC)Π/2, switch S2 is closed and S1 is opened. After switch S2 is...
  16. P

    How do I find out the flux for an air core inductor

    How do I find out gauss from air core inductor 36mohm pumped with ~130amps 9ms long? http://www.parts-express.com/erse-25mh-14-awg-perfect-layer-inductor-crossover-coil--266-380 Greatly appriciated.
  17. J

    AC voltage source driving an inductor and a capacitor

    Homework Statement Homework EquationsThe Attempt at a Solution I don't understand why would the current be zero in any of the branches . May be I am missing something very fundamental . Please help me understand this question .
  18. slow

    Understanding the Coaxial Inductor: A Study of its Electric and Magnetic Fields

    I want to expose something that caused me a lot of curiosity. First of all, I beg you to point out my mistakes and, if there are any insurmountable ones, help me to understand them. I start by presenting a figure. It is a solenoid that differs from the common case, because the wire at one end...
  19. J

    Time constant of an inductor coil

    Homework Statement Homework EquationsThe Attempt at a Solution I think I can solve this problem . But I am bit unsure about how current changes in the circuit and the coil when it is shorted . Before the coil is shorted , there will be no induced EMF across the terminals of the coil ...
  20. M

    Hello, ferrite rod coupling inductor, I dont understand

    hi to everybody, can somebody tell me, ferrit rod coils, is a transformer? if yes how do you calculate? what is the formula how you select the coupling inductor L2 or L3... because like i read the maing inductor must connect to capacitor(for frequency to find min and max i understand) but...
  21. R

    Finding the maximum value of current through the inductor

    Homework Statement Homework EquationsThe Attempt at a Solution [/B] I got the first 2 parts, but I'm having trouble with the last one. For the time the switch S1 is closed, I derived ##q(t) = CE(1 - \cos(\frac{t}{\sqrt{LC}}))##, by writing the loop equation ##\frac{E}{L} - \frac{1}{LC}q =...
  22. A

    Independence of Currents in Inductor-Switch Circuit

    In circuit like this If I closed the switch "s" Are the currents in mesh "I1" and "I2" independent of each other? if yes Why /why not? Thanks.
  23. G

    Engineering Inductor circuit time constant

    Homework Statement Hi. I started studying LR circuits and the first thing that made me do searches in textbooks of mine and in the internet was the time constant which is surprisingly not L times R, but L/R which would mean the time needed to store and release energy is being prolonged with...
  24. R

    What happens to the energy in an inductor or capacitor when opened?

    Hi guys..i have got a question...suppose i connect an inductor to a dc source until it is fully charged..as soon as it gets full of magnetic energy,i disconnect it from the circuit..remember that it has magnetic potential energy..suppose an idiot like me opens up the inductor (as inductor is...
  25. J

    Coupled inductor boost converter - Ripple current

    I am trying to calculate the ripple current in boost converter for ∆i1 and ∆i2 between time intervals between DT and T, and also dependent on the voltage level (Vin or Vin-Vout). To find a formula for ∆i1 and ∆i2, two formulas have to be derived for them. This is done from the equation: I...
  26. D

    Two AC Sources with One Transformer

    I want to program a little power grid game and have the problem of connecting things via transformers. Imagine the following setup: You can see the AC voltage sources as generators (or together with the resistor as a "consumer", if the amplitude is 0). What I need to figure out are the...
  27. J

    Energy absorbed by the inductor in 4 seconds

    Homework Statement Homework Equations V = L di/dt Energy = V*I*t The Attempt at a Solution First we find out V across L This V will be there only for 1st 2 seconds as after that there is no change in current. So V(across L) is L * di/dt = 2 * 6/2 = 6V equation 1 Now Current is a function...
  28. R

    Magnetic field and Poynting Flux in an Inductor

    Hi everyone, Lately I have been studying the Poynting Flux and I am familiar with the classic examples of how it can be used to describe the power being dissipated by a resistor and the energy flowing into a capacitor, but I have never come across a similar analog for how the Poynting flux...
  29. W

    Self-Induced Emf and Angular Frequency

    The context is an ac circuit with only one element - the inductor. My textbook says that the self-induced emf increases with increasing angular frequency, but I'm having trouble seeing this mathematically. If self-induced emf = ε = -L(dI/dt) and L = X/ω, then emf and ω are inversely related...
  30. Drakkith

    Why is the voltage across an inductor negative?

    I think I must have missed something when going over inductors for my electric circuits class. The voltage across an inductor is described by the equation: ##V(t) = L\frac{di(t)}{dt}## For the case where current is flowing through the inductor until ##t=0##, at which point the voltage/current...
  31. Drakkith

    Max Energy Stored in an Inductor

    Homework Statement Find the maximum energy stored in the inductor. Homework Equations ##p(t) = 0.09375te^{-1000t}(1-500t)## The Attempt at a Solution [/B] So, I've been working my way through a multi-apart problem and one part asks me to find the maximum energy stored in an inductor. Given...
  32. R

    What Happens to the Current Through an Inductor When the Switch Opens?

    Homework Statement "The switch in the circuit in the figure has been closed for a long time and is opened at t = 0. Find i(50 ms)." I attached an image of the circuit below.Homework Equations KVL: Ri + q(t)/C - q(0)/C + vc(t) + Li' = vs(t) Li'' + Ri' + i/C = vs'(t) Where vc is voltage across...
  33. V

    Magnetic field and inductor

    Homework Statement Homework EquationsThe Attempt at a Solution In this problem as the rod moves towards right, magnetic force of magnitude ilB starts acting towards left on the rod.This decreases the speed of the rod .The EMF induced in the rod is Blv where v is the instantaneous speed of...
  34. M

    Excess charge in inductor due to selfinductance

    How does one calculate an excess charge distribution across 100 mH single layer inductor with 30 Hz voltage at amplitude of 10 V ?
  35. L

    What is the current in these 3 circuits right after the switches are opened?

    Homework Statement What is the current through the resistor marked 'R' in all three circuits just after the switch is reopened after being closed for a long time? The Attempt at a Solution The explanation that we were given for (1) is that I = V/2R and (2) I = V/3R and (3) I = V/(R/2) but I...
  36. J

    Calculate voltage drop across the inductor

    Homework Statement An inductor of negligible resistance and an inductance of 0.2 H is connected in series with a 330 Ω resistor to a 12V d.c. supply. Determine: (b) the voltage drop across the inductor after two time constants(c) the voltage drop across the resistor after three time...
  37. A

    Why the inductor voltage blows up for a sudden current change?

    Dear All, This is my first question to the forum. "Assume there is a + dc voltage across a inductor. So current will continue to increase. Now if the current through the inductor is forced to stop using some means ( eg. Current was flowing in inductor through a ON switch and then switch turns...
  38. A

    Why inductor voltage blows up for a current change?

    Dear All, This is my first question to the forum. "Assume there is a + dc voltage across a inductor. So current will continue to increase. Now if the current through the inductor is forced to stop using some means ( eg. Current was flowing in inductor through a ON switch and then...
  39. Pushoam

    Inductor as a battery in a circuit

    Homework Statement Can we consider an inductor as a battery of emf ξ = -## L \frac {dI } { dt} ##? For the above circuit, ##V_A - V_B = V_C -V_D \\ -L \frac {dI } { dt} = IR ## Here, the inductor is acting as a battery of emf ## -L \frac {dI } { dt} ##. For the above circuit, ##V_A - V_B...
  40. V

    Induced current in an inductor

    I am struggling with the concept of induced current in a circuit consisting of an inductor and how that induced current establishes back EMF . Please see the page of the textbook attached . There is a circuit consisting of an inductor , a series resistance (not shown) and a battery ( not shown...
  41. P

    Capture Energy from Inductor to Power Load

    This post is inspired by a lesson on the allaboutcircuits education website. In chapter 15 of Direct Current there is a heading "Inductors and Calculus" - https://www.allaboutcircuits.com/textbook/direct-current/chpt-15/inductors-and-calculus/ At the bottom of the topic there is a circuit...
  42. P

    Inductor behaviour in an AC power supply

    what is actually happening when an Inductor is connected with an ac source.(i mean at the very instant of connection is made).i know emf will be induced due to change in current.(curl of E is =-time derivative of B)here my confusion is,inorder to induce emf,current should flow first,then who...
  43. Nikhil N

    What could be the ratings of inductor used?

    I have a circuit which can produce bursts of 500V. When I did this circuit, The 2.2 mH is burning. I want to know whether do we need to take care the power rating of inductor? After the test I tried the experiment without inductor too. I have used 2.2ohm, 1W resistor. That too started to burn...
  44. Vanessa Avila

    (LC Circuit) Finding cap charge after connecting to inductor

    Homework Statement A capacitor with a capacitance of C = 5.95×10−5 F is charged by connecting it to a 12.0 −V battery. The capacitor is then disconnected from the battery and connected across an inductor with an inductance of L = 1.50 H . What is the charge on the capacitor after a time...
  45. S

    Inductor leading lagging voltage-current

    Trying to understand how in a conductor in an Ac circuit, the voltage leads the current. AS far as i read the voltage and the current max do not peak at the same time? Also because of lenz law the behavior of the coil resist the build up of the current so it takes time for a change in voltage...
  46. S

    Solving Inductor Circuit Homework Problems

    Homework Statement For the circuit shown in the figure, the inductors have no appreciable resistance and the switch has been open for a very long time. (Image of circuit) (a) The instant after closing the switch, what is the current through the 60.0-Ω resistor? (b) The instant after closing...
  47. G

    I Induced EMF in a half vs. whole ferrite toroid

    Hello all - I've stumbled upon what seems to be a pretty basic magnetic materials question that's got me stumped. Maybe one of you can help me figure this out. I did the following experiment (see figure below): Put a ferrite toroid around a current carrying wire carrying 12 Amps RMS at 120V...
  48. jlmccart03

    Find current through inductor after many time constants.

    Homework Statement In the figure, R = 1.9 kΩ and ε0 = 60 V . When the switch is closed, the current through the inductor rises to 10 mA in 30 μs . What will the current in the circuit be after many time constants? Homework Equations I = V/R or I = ε/R if current is constant which after many...
  49. S

    Does frequency affect inductor and capacitor value

    Hi , I was measuring the inductor and capacitor value of a resistor bank with a 100Hz and 1kHz using a LCR meter by fluke. I realize that with different frequency, the L and C values were different. If the measured values were the inductance and capacitance I can understand that it changes...
  50. G

    Why is EMF (ElectroMotive Force) equal to a voltage?

    Hello. Let's say a current i(t) flows through an inductor of solenoid type. Time-varying i(t) generates a magnetic field B(t) inside the magnetic core of the inductor. As B(t) is time-varying, EMF, which is the line-integral of the induced electric field E(t) along a coil (which carries i(t))...
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