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. J

    Calculate Inductor Maximum Energy: 240V, 50Hz, 4A & Negligible Resistance

    Homework Statement Assuming steady-state sinusoidal ac.A voltage of 240V at 50Hz applied to an inductor yields a current of 4A.Assume negligible resistance.Find inductance, max stored energy. Homework Equations E=0.5Li^2 X=2*pi*f*L The Attempt at a Solution V/I=X Which I...
  2. J

    Ferrite core variable inductor

    Hi all, I'm working on designing a variable inductor using a ferrite core. The basic idea is that I have a large wound inductor on the central arm which I pass a DC-current through, and a smaller, variable inductor on one of the side arms. As you increase the current through the main winding...
  3. A

    How Does Energy in an Inductor Change When Disconnected?

    Homework Statement Not really relevant here. Homework Equations U = LI^2 -- maybe? The Attempt at a Solution http://i.imgur.com/Pq4dOex.png The picture is there, as well as the answer. Why is that the answer? How do inductors work when completely disconnected, and not in a...
  4. K

    Calculating turns in an inductor

    Homework Statement Hey everyone, I got a question wrong on my homework that I'm trying to figure out. I'm given this: "a 500uH solenoid(inductor) with an air core is 10cm long has an inside diameter of 1cm. How many turns of wire does it have? Homework Equations L = N2*u*A / l...
  5. N

    Current through an inductor connected directly to a battery

    Homework Statement A long, fine wire is wound into a coil with inductance 5 mH. The coil is connected across the terminals of a battery, and the current is measured a few seconds after the connection is made. The wire is unwound and wound again into a different coil with L = 10 mH. This...
  6. X

    Resister inductor - calculate resulting impedance

    resister // inductor -- calculate resulting impedance Hello, how 600Ω || 300jΩ = 120 + j240 ?? how do you get the value 120 + j240 from 600 register parallel wih 300jΩ inductor?
  7. G

    Finding resonance frequency of non ideal inductor

    Homework Statement We have this circuit: (uin+)---[1/jωC]--[jωL]--[RL]----o------uout+ (resistor of value R connecting the two lines at their o's here) (uin+)-------------------------o------uout- Find an expression for the quotient of u(in)/u(out), and then find the resonance...
  8. B

    Potential difference across an inductor

    I have some confusion about how emf across an inductor is generated: The potential difference across an inductor is an induced emf produced by the changing magnetic flux through the coils of the inductor. In general, electric potential is a scalar potential of the electric field. Hence the...
  9. J

    Deriving inductor voltage equation

    Hi guys, So I'm starting to learn about magnetic fields and electrics fields, one of the equations we use is v= -L*di/dt ... I've been trying to figure out how it's derived, in my book it says: it starts off like this: 1. v=-dθ/dt (faraday's law) <- why is there no N(no. of turns)...
  10. M

    Need help about reactor (inductor)

    Can someone help me solve this? I don't really understand how to do this. A 1kvA reactor's capacity is needed to be enlargedto 81kvA. How much does its dimension needs to be multiplied? Hint: when its dimension is m times enlargened, surface A'=m'A, flux ∅'=m^2∅, current I'=m^2I, voltage...
  11. S

    CAN Current pass Through INDUCTOR in Ac circuit

    CAN Current pass Through INDUCTOR? how the AC circuit is completed when Inductor is in it as no AC pass through it?
  12. O

    Current phase between inductor and capacitor in LCR-circuit

    At resonance (## \omega_0^2= 1/LC##) in an LCR-Circuit the phase angle given by \theta=\tan^{-1}\left( \frac{\omega L - 1/\omega C}{R} \right) obviously is zero. And still there are other phases to deal with. This I don't understand. Let me elaborate. For example when calculating the amount...
  13. P

    When we apply AC to an inductor

    "when we apply AC to an inductor (pure inductance), the current will lag the applied voltage by 90 degrees. " how this happens? why current lags applied voltage by 90 degrees? :confused:
  14. A

    What is V(K) of inductor given coupling coefficent?

    Homework Statement Homework Equations k=1 inductor(left)=400j inductor(right)=1600j The Attempt at a Solution how to do this! help me. my caluclator can't solve 3 rectangular form mesh currents equations so i cannot solve for individual currents for all 3 loops! i just guessed...
  15. A

    Inductor and capacitor as current and voltage sources

    Hi, I have just seen this statement in another forum: An inductor is a constant current source for a limited time until its energy is expended. A capacitor is the counterpart being constant voltage until its energy is spent. I am not quite understand it. Can you help me? This is not a...
  16. H

    Calculate DC current through an inductor?

    Hi everyone, Say I have a series DC circuit. The circuit contains a 100V DC source, a switch, a 1.5H inductor, and a 1nF capacitor (all in series). If I close the switch for 2uS what is the current at that time? Initially I thought I could rearrange V=L*di/dt to V*Ton/L = di/dt which would...
  17. A

    Why is the electric field inside an ideal inductor zero?

    This is really not a homework, just need help to understand some concepts. In a circuit includes R, L, C in series, we apply Faraday's law: I*R + Q/C + 0 = - dψ/dt Here VL = ∫E*dl across the inductor is zero. I know this because the inductor has no resistance and according to Omh's law VL =...
  18. P

    Current in inductor used to measure EMF.

    Hi, Homework Statement This is not a formal HW question, yet I was wondering whether one of you might be willing to answer it nevertheless. According to Fraday's law, ε = -∂\phi/∂t. If I reversed the direction of the current in an inductor used to measure ε, would that have any effect on...
  19. H

    Calculating B of inductor operating in continuous conduction mode?

    Hello everyone, I am working on a coil design and have a question. The coil is meant to operate in continuous conduction mode, so the current waveform is a ramp waveform. B=V*t / N*Ae When calculating V*t do I use 1/2 t (since the current only increases for the first half of the...
  20. M

    Inductor opposing change in current.

    Hello, I'm wondering, if you have an inductor and resistor that has the switch open, so current is zero. Then you turn on the switch, the inductor is going to resist this change, it wants to be zero, right? Therefore, why doesn't the current indefinitely stay as zero, since the inductor would...
  21. A

    Equivalent Mutual Inductor Circuits

    Homework Statement Consider the circuit which consists of two ideal inductors L_{S} ,L_{P}. These inductors are magnetically coupled with mutual inductance, M. It is possible to replace these magnetically coupled coils by three coils which do not share magnetic flux linkages. The two...
  22. C

    Find current through inductor that parallels a resistor

    Homework Statement The switch in the circuit has been closed for a long time before it is opened at t = 0. Find: a. IL(t) for t > 0 b. i0(t) for t > 0 c. V0(t) for t > 0 Homework Equations equivalent resistance, equivalent current, equivalent voltage voltage...
  23. C

    Find the voltage of an inductor in an LR circuit

    Homework Statement at t=0 switch S is closed. Just after the switch is closed what are i1, i2, the potential difference across V2 across resistor 2, and Vl across the inductor? A long time after the switch is closed, what are i1, i2, V2, and Vl? Emf = 12V, R1= 15 ohms, R2 = 25 ohms, and L...
  24. P

    Find the impedance of capacitor and inductor with dependant current so

    Homework Statement From the circuit find the impedances of the capacitor and inductor Is(t)=15 cos(500t) A Homework Equations The Attempt at a Solution So is this right? Convert the 15 cos 500t into polar form, 15<0 I. Then the resistor is 8 ohms, so 15*8 = 120 V...
  25. P

    FM Radio receiver in RLC circuit with .200 microH Inductor

    Homework Statement The tuning circuit in an FM radio receiver is a series RLC circuit with a 0.200 µH inductor a. The receiver is tuned to a station at 104.3 MHz. What is the value of the capacitor int he tuning circuit? b. FM radio stations are assigned frequencies every 0.2 MHz, but two...
  26. B

    Role of power inductor in train applications

    I have a circuit-diagram for a train which in the final stages converts the power to a 3-phase AC voltage (IGBT) that is the excitation for the motors in the train. However, right before the converter module there is a power inductor. I have looked through some literature and on the internet but...
  27. A

    AC Passes Through Inductor: Fact or Fiction?

    While studying electrical science, I was told that when an alternating current passes through an inductor, current lags voltage by 90•. And when through a capacitor, current leads voltage by 90•. But while studying transistors in electronics, I was told that AC passes through a capacitor but...
  28. H

    Requirements for inductor to operate in continuous conduction mode?

    Question about continuous conduction mode converter I have a few quesitons about CCM converters I have posted a basic schematic of the circuit in question as an attachment. The circuit is a series LC circuit in which the inductor and capacitor charge during the on time. During the off time...
  29. B

    Potential difference of an inductor equal to minus the induced emf?

    Hi, Two questions I'm finding it hard to get my head around with inductors... Say we have an increasing current, this is going to cause an increase in flux in one direction, which will induce an emf to drive a current which produces a magnetic field to oppose the change in flux. Than doing...
  30. L

    Inductor saturation due to high dv/dt

    I have a buck regulator running hot. I reduced the switching frequency and the temperature is almost normal. The current rating of the inductor is high(2A) compared to current consumption on the board (300mA). Why does reducing the switching frequency solve the heat problem? Does the...
  31. P

    Making a 10mH Inductor Coil for an LCR Resonant Circuit

    i have to make a 10mH inductor coil for an LCR resonant circuit.could someone please guide me on which gauge of wire to use and how to wind it to make a coil within 5% variation? i need the coil to be close enough to 10 mH for resonance. looking forward to ur help...
  32. C

    Engineering Circuit with inductor; find current for t>0

    Homework Statement http://imageshack.us/a/img832/1651/homeworkprobsg32.jpg At t= 0, the switch is opened. Calculate the current i(t) for t>0 Homework Equations V(t) = L* dI/dt V = IR I = V/R voltage division, current division, KCL, KVL The Attempt at a...
  33. xconwing

    How to Simplify Inductor Expressions Using Calculus?

    How can you get from the first expression to the second. I've done calculus, just need a fresher. I don't know how to deal with the dt/dt thanks
  34. J

    Basics question of Inductor to powering high voltage lamp

    I was trying to study the inductor role in Flyback converters and all, they seem to rely on the principle that the inductor is first energized while the switch is closed and then, it acts as a voltage source itself when the switch is opened. All that is good, but I am confused with the...
  35. J

    Engineering Calculating when voltage across resistor = voltage across inductor in an RL circuit

    Homework Statement A step input of 100V is applied to a resistor of 50Ω in series with an inductor of 10H at time t=0. Calculate the time at which the voltage across the resistor equals the voltage across the inductor Homework Equations Im not sure which equation to use, i know τ=L/R...
  36. S

    Inductor Basics: 2 Windings or More?

    The other day one of our power labs we were using rather large inductors; that is, approximately 10"x4" in the shape of a doughnut. There were 4 connections into the inductor. We connected a wire from one to the other, and then used the other two connections as any other inductor. Does that...
  37. S

    Calculating Inductor Loads in Circuits

    I did an exercise today on my breadboard with an inductor that I made from a coil of 22 gauge stranded hookup wire wrapped in a helix coil around a 60d nail I found in my garage. The power source was a 9V battery. I took a measurement of just the battery fully open with my digital volt meter and...
  38. S

    Rate Of Change Of Current In An Inductor

    Homework Statement A coil has self inductance L of 2 Henrys, and a resistance R of 100 Ohms. A DC supply voltage E of 100 volts is applied to the coil. Show graphically the approximate rate at which the current increases at the moment of switching on (t=0) and after 10ms. Confirm your...
  39. J

    Ansoft Maxwell 3d Closely coupled inductor

    Hello! I am having an issue with getting any graphs on inductance or induced voltage. In the attached circuit: What I have is a 28Vac source w/ 400hz and 2 coils (R=18.6ohm each) that are connected with a common. In the model: I have a core in the center that will be able to move up...
  40. D

    How can I measure the shunt capacitance of an inductor?

    I know that the there is some small capacitance between the windings of an axial inductor let's say, but how does one measure this? The inductor is a short on an LCR meter...
  41. L

    Instantaneous current in a reisistor, capacitor and inductor

    Homework Statement a resistor, a capacitor and an inductor are connected in parallel to a source of oscillating EMF of frequency 955hz and amplitude of 1.0x10^3 V. the resistance of the resistor is 200Ω. what is the maximal instantaneous current in the resistor? if we want to make a maximum...
  42. R

    How does the size of a loop affect the storage of energy in an inductor?

    The standard explanation is that the magnetic field stores the energy but when I start considering different sizes of a single loop inductor with a current flowing in it things start to get a bit vague. As the loop diameter is increased the inductance goes up so the single loop can store more...
  43. J

    Calculating the equivalent inductance of a simulated inductor

    Homework Statement I am asked to find the equivalent resistance of a simulated inductor shown above. We are told not to worry about the simulated inductor circuit. The simulated inductor will be incorporated into a larger circuit as shown below. 2. The attempt at a solution I am really...
  44. B

    The current in an inductor when energy is stored. Please help

    The current in an inductor when energy is stored. Please help! Homework Statement What's the current in a 15mH inductor when the stored energy is 42μJ Homework Equations E = 1/2 L i^2 The Attempt at a Solution .000042J = (.5)(.015H)(i^2) .000042J = (.0075)(i^2) .0056 =...
  45. M

    Electric fields in an Inductor

    En and Ec are the non-conservative and conservative electric field respectively. I've quoted this from the textbook I'm using (University Physics by Young and Freedman 12th edition). Now, it seems to me that the author just invoked the assumption that the inductor have negligible resistance...
  46. D

    What is the voltage over a non-ideal inductor with a resistance of 50Ω?

    Homework Statement An inductor is subjected to the current in the graph: L = 100mH = 0.1H I) Calculate and graph the voltage over the ideal inductor. II) Repeat for non ideal inductor with a resistance of: RL = 50 Ω Homework Equations U_{L}=L*\frac{di}{dt} U_{av}=L*\frac{Δi}{Δt} The...
  47. U

    How much current is needed in an inductor to heat up water?

    Homework Statement How much current is needed in a 9.00mH inductor so that the stored energy will be enough to heat 285g of water from 20.0 degrees Celsius to the boiling point of 100 degrees Celsius? Specific heat of water is 4190 J/kg*Celsius. Homework Equations q = cm(change in T) The...
  48. A

    Engineering Current through inductor in a circuit with a sinusoidal voltage source

    Homework Statement http://www.wifstrand.se/Albert/stuff/p7.7-1.png Homework Equations vL = L * (diL / dt). All of the inductors can be reduced to a single 8 H inductor, so iL = (6 / 8) * ∫ cos 100t dt = 0.0075 sin 100t if you integrate from 0 to t. The Attempt at a Solution The formula...
  49. R

    Determining Steady State Current in an Inductor Transient

    1. The problem statement See attached question - So I have this inductor transient question and can't seem to get the right answer. Basically I don't know how to determine the current in steady state after switch operation.Homework Equations tau = L/C iL = a+be-t/tau V=IR The Attempt at a...
  50. G

    Circuits Question - Voltage and current in an inductor circuit

    Circuits Question -- Voltage and current in an inductor circuit Homework Statement See Attached Homework Equations The Attempt at a Solution I found Zeq and there are exactly 2 Amps going into it. I'm not sure what to do from here. Z_{eq} = \frac{<(arctan(\frac{R}{ωL}))}{ω^{2}L^{2}+R^{2}}...
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