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. ElijahRockers

    Engineering Inductor Circuit, separation of variables

    Homework Statement V_o varies as V(t) = 2000e^(-100t) volts for t > 0 i1(0) = -6A i2(0) = 1A thus i0(0) = 5A Find i0(t) for t > 0. I found Leq = 4H V(t) = L di/dt I separated variables and integrated, got 5e^(-100t) but the software is telling me it's wrong... supposedly the answer is...
  2. Z

    Engineering Inductor Voltage Maximum and Maximum Voltage Calculation

    Homework Statement The current in a 25mH inductor is known to be - 10A for t <= 0 and (-10cos400t - 5sin400t)e^-200t A for t >= 0. Assume the passive sign convention. Part A: At what instant of time is the voltage across the inductor maximum? Part B: What is the maximum voltage...
  3. J

    Finding the time constant of an inductor

    Find the time constant τ for the first order response of the circuit below at t > 0 s. L = 6 H R1 = 8 Ω : R2 = 6 Ω Give your answer to at least two decimal places, in s. I am really struggling on where even to begin with this question. I know that for a simplified circuit t = L/R And...
  4. P

    Energy Stored in an Inductor, calculating inductance

    Homework Statement The electric-power industry is interested in finding a way to store electric energy during times of low demand for use during peak-demand times. One way of achieving this goal is to use large inductors. What inductance L would be needed to store energy 3.0 (kilowatt-hours)...
  5. A

    Increasing Inductance with Iron Core?

    If I wrap a wire around a permanent magnet (iron) to make an inductor... will that increase the strength of the inductance? Or just push the inductor into magnetic saturation? What if I just use a solid ferromagnetic core (not magnetized) such as an iron or steel rod? How much does that...
  6. B

    Dependent source parallel an inductor with a sinusoidal source

    an independent source with a forcing function modeled by cos(500t) is in series with an 100 ohm resistor. A dependent (current controlled) source is placed across the remaining resistor terminal and ground. A 0.3mH inductor is in parallel with the dependent source. The value of the dependent...
  7. N

    Frequency applied to Cap & Inductor

    1. The problem statement 1kHz is applied to 1000 μF Capacitor, What is its Capacitance? & 1kHz is applied to 10 H inductor, What is its reactance? The Attempt at a Solution using x= -1/ωC = -1/2∏∫C I came up with 159 fF then for question 2 I got using Xl=2∏FL (better seen here...
  8. P

    Disconnecting source from inductor

    Hi, I'm working through a power electronics book and I'm looking at a half-bridge transformer-isolated buck converter (attached page). I've run into something that I can't fully understand even though the author presents it as something obvious. At 0 < t < D*Ts, the Q1 FET is conducting, and...
  9. N

    Inductance of inductor in large steady state magnetic field

    So would the inductance of a inductor be effected if it was in a large steady state magnetic field. Say the inductor produces a field of about .01 Tesla and the large electromagnet produces a field of 1 Tesla or more. How would a high permeable core vs a air core effect it? Would it add...
  10. J

    Thermal Properties of an Inductor

    What properties of an inductor change in a low temperature environment. Specifically in the -100 through -70 degrees Celsius range?
  11. N

    Integrating an Inductor on a Chip / Die / Package?

    Can someone tell me what the benefit of this is, and why it's been traditionally very hard? I've heard that many RF applications now do an S-i-P integration of an inductor, possibly for spatial and cost reasons.. What would be some considerations, though (i.e. does the inductor add any noise...
  12. F

    Current through short-circuit inductor

    Hi, If we short circuit a simple basic inductor in an AC system, what happen to the inductor and the current at the branch? Inductor do not has resistance, so do the short circuit line. Does the current will divide equally through each branch and only some lagging at the inductor branch ...
  13. R

    Multiple inductor or capacitor RLC circuits

    So I know that the equation for the natural frequency of an RLC circuit is: ω0=(LC)-1/2 I'm just wondering how this would change for a circuit with more than one inductor or capacitor. Say for instance an inductor in parallel with a capacitor, both connected in series to another inductor...
  14. R

    Multi inductor or capacitor RLC circuits

    So I know that the equation for the natural frequency of an RLC circuit is: ω0=(LC)-1/2 I'm just wondering how this would change for a circuit with more than one inductor or capacitor. Say for instance an inductor in parallel with a capacitor, both connected in series to another inductor...
  15. C

    Calculate the energy stored in Capacitor and Inductor

    Homework Statement A circuit consists of an 800mH inductor, a 20mF capacitor, and a switch, all in series.The capacitor is charged with an initial charge charge of Q = 400mC, and the switch is closed at t= 0. Calculate the energy stored in the Inductor and Capacitor at t = 100ms. Homework...
  16. F

    Self-Inductance of an Inductor

    Homework Statement An inductor has a current I(t) = (0.480 A) cos[(280 s-1)t] flowing through it. If the maximum emf across the inductor is equal to 0.490 V, what is the self-inductance of the inductor? Homework Equations ε = -L*di/dt The Attempt at a Solution I would have that...
  17. N

    Bilifar Coil Inductor Q&A: What Happens When Powered On/Off?

    I have a question about a bilifar coil. First I need to set the image, You have a opposing bilifar coil so as to decrease the inductance of the coil. http://en.wikipedia.org/wiki/Bifilar_coil 1 Winding will be coil A and the other coil B just so we can all know which coil turn we are all...
  18. A

    Understanding Inductors in Electrical Circuits: Exploring the Basics

    Hi can someone please elaborate on the explanation our teacher gave us.
  19. F

    What is the reason behind inductive reactance in an AC circuit?

    This is quite a frustrating problem for me so hopefully somebody can describe it in such a way that it settles in my mind. It is the concept of voltage and current being out of phase. Inductors are frequently described as responding to changes in current but does this really make sense...
  20. C

    Find Inductor Value to Limit Current Increase in Circuit

    Homework Statement Your circuit has a resistance of 175Ω and an ideal battery with an emf of 6.3V. What value of inductor should you add to the circuit to ensure the current increase in the first 58μs is less than 4.9mA? Homework Equations I think E=L(di/dt) The Attempt at a...
  21. S

    Hysteresis losses in an inductor - resistance proportional to frequency?

    Homework Statement Consider an inductor, with a core of ferromagnetic material, connected to an a.c. power supply. Explain why the contribution of the hysteresis losses to the resistance of the coil is theoretically proportional to the frequency of the oscillator. The Attempt at a...
  22. G

    Piece of metal being carried through an inductor

    Hi, I have some questions about a piece of metal traveling through an inductor with DC current flowing through it. Imagine a solenoid of sorts with a hole in the middle that a piece of neutrally charged metal travels through, sort of like a coil gun. Let's say the inductor has no current...
  23. H

    Calculating q factor of an inductor

    I have some old ignition coils that I would like to compare. I have set the secondary to resonate with a .47 mf capacitor and these coils will resonate at 50 to 70 hz. The problem is, I can't really compare them as the center frequency is different on each. Is there a way to test their q...
  24. B

    How does the inductor differ from the antenna?

    I've been trying to figure out how an inductor is different from an antenna. It's obvious that the inductor has more inductance than an antenna would, but let me try to explain it from my point of view. My current research project for school (lasting this year and into my senior year) is on the...
  25. K

    Why does the resistance of an inductor increase when an iron core is introduced?

    The inductor is initially an air cored one.When the Iron core is introduced,the resistance is found to increase considerably.Please explain.
  26. S

    Inductor lightbulb circuit.

    I cannot seem to solve this problem: A typical "light dimmer" used to dim the stage lights in a theater consists of a variable inductor L (whose inductance is adjustable between zero and Lmax) connected in series with the lightbulb B as shown in Figure 31-36. The electrical supply is 240 V...
  27. O

    Energy stored in an inductor of an LR circuit

    Homework Statement An LR circuit has a resistance R = 25 Ω, an inductance L = 5.4 mH, and a battery of EMF = 9.0 V. How much energy is stored in the inductance of this circuit when a steady current is achieved? Homework Equations \epsilon= -d\phim/dt=-L\frac{dI}{dt} Um=\frac{1}{2}LI2...
  28. J

    Find power when resistor, capacitor, and inductor are connected in a series

    Homework Statement When a resistor is connected by itself to an ac generator, the average power delivered to the resistor is 0.952 W. When a capacitor is added in series with the resistor, the power delivered is 0.477 W. When an inductor is added in series with the resistor (without the...
  29. Y

    Inductor Impedance vs Inductive Reactance: Clarification Needed

    Hello, i just want to clarify, is there a difference between the inductor impedance or inductive reactance XL. inductive reactance XL = 2pi*fL is this the same for inductor impedance? i see on an example where they ask you to calculate the reactance in a series RL circuit. V= 100, f=...
  30. S

    Inductor considered as a broken wire.

    I quote from my book: "Just after the switch is closed, the inductor acts to oppose a change in the current through it." "Because the current through each inductor is zero before the switch is closed, it will also be zero just afterward. Thus, immediately after the switch is closed, the...
  31. F

    Is the Inductance of an Ideal Transformer Infinite?

    Is it valid to say that an inductor stores power? I know an inductor stores energy in its magnetic field. Power = dE/dt so is it right to say that power is stored in the magnetic field? Or is this completely wrong, and inductors don't absorb power at all? Thanks.
  32. L

    Buck converter inductor current at start up

    I am trying to understand the inductor current ramp up to steady state in a buck converter. I don't understand why the inductor current slope is not steep in the beginning. Let's say Vin=12v, Vo desired across the capacitor is 5V. Switch turns ON, Inductor current ramps up. Switch...
  33. A

    College Physics Problem Capacitor / Inductor

    A 10.0 Microfarad Capacitor is charged to 170 Micro Coulombs then connected across the ends of a 4.00mH inductor. (a) Find the maximum current in the inductor. (b) At the instant the current in the inductor is maximum. How much charge is on the capacitor parallel plates? (c) Find the...
  34. E

    Alternator Inductor Coil Output Equation (?)

    Hello!I'm working on an experimental alternating current generator project and need specific equations to calculate voltage and current output from a permanent magnet driven inductor, so I will have an idea what to expect before I commit real money to expensive materials. the only variables...
  35. W

    Strength of induced magnetic field inside an inductor

    I am trying to make a crude coil gun. I remember that if I run current through a coil of wire, it generates a magnetic field according to the right hand rule. Will the inductance of the coil of wire greatly affect the strength of the magnetic field, or is it mainly due to the strength of the...
  36. D

    Electrically Variable Inductor

    I have an inductor in a design that is one half of an air coupled RF transformer. The operating frequency is 50 MHz. The purpose is to provide power to the load side. It is for all intents and purposes an RF to DC power supply design over some gap. The primary is the fed radiator inductor, a...
  37. K

    How to make inductor coils?

    I am looking forward to a small project. For this i need some inductor coils. I searched through the local shops, but i could find any inductor coil. According to what i know inductor coils are made by making loops using wires. http://www.instructables.com/id/Making-a-Simple-Induction-Coil/ Is...
  38. A

    Why is the minus sign omitted in the voltage across the inductor?

    According to faraday's law the governing equation is emf=-d(flux)/dt.But we usually write the voltage across the inductor as v=d(flux)/dt.What happened to the minus sign?
  39. D

    Calculating t1: Current Through an Inductor

    Homework Statement The circuit parameters are: R = 60 Ohms, L = 5 mH, C = 40 microFarads, and e= 120 V. Initially the switch has been closed for a long time. At t=0 the switch is opened. What is t1, the first time greater than or equal to 0, that the current through the inductor is equal...
  40. T

    Time constant for an inductor?

    The original question: Notice that they have marked that the correct time constant is T = 2L/R Why is this the correct answer and not L/R? I thought the inductor will only take into consideration one Resistor as in both circuits (switch closed vs open), current will only flow through...
  41. M

    Understanding the Behavior of Inductors in AC Circuits

    If you have an alternating voltage source in series with one inductor what happens? The book has a graph of the alternating voltage source and the current through the inductor. What I don't understand is how there is current in the inductor at t=0. If you look at how I solved the problem I...
  42. B

    Inductor, switch, snubber diode(flyback diode)

    Hello, I am designing a simple circuit and I need some guidance over snubber diode. When we open the switch, when we have a inductor in circuit, we will have that arc over switch which is something that we don't want. Using this snubber diode, we can avoid this. I feel that we will...
  43. S

    Time constant for the current through the inductor

    Homework Statement http://i.imgur.com/wjD8Y.png In the circuit below, V = 6 volts, R = 10 ohms, L = 100 mH. The switch has been open for a long time. Then, at time t = 0, the switch is closed. What is the time constant for the current through the inductor? 2L / R...
  44. H

    Pulsed DC into inductor turns to AC?

    What is it that causes pulsed dc into an inductor to turn into ac? Are their specific frequencies at which this occurs (i.e. inductors self resonance frequency)?
  45. S

    Why does the impedance of inductor change with frequency?

    The power stored in an inductor is E=0.5LI2 which is independent of frequency However, the impedance is ωL. So, what makes the impedance increase with frequency?
  46. M

    DC Circuit and an Inductor - Q on potentials

    Homework Statement While the voltage induced between the points P and Q is changing, which is the high potential end of the inductor? Explain your answer. P.S. sorry for the fail Paint job lol Homework Equations The Attempt at a Solution I know that in a DC circuit current flows from the...
  47. P

    Why Does Inductor Voltage Drop Oppose Electron Flow?

    This is not a homework question. Why is the voltage drop on an inductor opposite the electron flow? "When the current through an inductor is increased, it drops a voltage opposing the direction of electron flow, acting as a power load. In this condition the inductor is said to be charging...
  48. Todee

    Want to find the current of inductor .

    Homework Statement Consider a 50 mH inductor . find i at t=10 ms if v= 20t^2 V for t>-0.1 ms and i(-0.02)=5 mA.
  49. L

    About the experiment to find the reactance of inductor

    I have just done an experiment on finding the reactance of (a)an air-core inductor and (b)an inductor with a soft-iron core. I have plotted a graph of Vrms against Irms for each experiment. For the graph in (a), the straight line can pass through origin; yet, for the graph in (b), the straight...
  50. G

    Variable Voltage, Two inductor, One capacitor Circuit

    Homework Statement http://imageshack.us/photo/my-images/101/circuitk.jpg/ The question asks you to demonstrate what I0(t) and I1(t) are, it gives you the solutions.Homework Equations V(t)=Vcos(wt) I0(t)=(V/wL)((w0^2-w^2)/(2wo^2-w^2)) I1(t)=(V/wL)((w0^2)/(2wo^2-w^2)) The Attempt at a Solution...
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