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. B

    Understanding Inductors in Initial Phase: Voltage and Current Behavior Explained

    Everybody on the internet talks about inductors when they are in steady state. But nobody talks about inductor, when its in initial phase. Here is what I am talking about: We made a clear statement why voltage leads the current in inductor. And I understood that part quite well. But...
  2. genxium

    Phase Difference?(Mutual Inductor)

    Homework Statement For a mutual inductor component like this, <C1,L1> is resonant to f0, <C2,L2> is also resonant to f0 too, and the mutual inductance between L1 and L2 is M, and M is very small so that it could be ignored in approximation. Assume that the voltage Vin on <C1,L1> is the...
  3. E

    Tesla coils / Toroidal inductor flux

    I've been reading up on tesla's wireless power transmission lately, and I've been wondering how magnetic flux through the center of a toroid induces a voltage in its coils. From what I understand, the time derivative of magnetic flux through a loop is proportional to the induced voltage...
  4. M

    Does the direction of winding affect the induced emf in a an inductor coil?

    Hi, What if the inductor coil is wound one way rather than the other. Then the circular flow of current will be clockwise in one case and anticlockwise in the other. And if the inductor is connected to an ac source, then the current will vary. Now in both the orientations, the variation...
  5. C

    Current through and inductor

    Homework Statement Find inductor current for t > 0 http://img192.imageshack.us/img192/5814/unledgo.png Switch is initially open and closes at t=0+ The professor wants us to solve these only using the Diff Eq approach. On other questions I would just do a KVL with the inductor loop and solves...
  6. H

    Difference between boost inductor and flyback inductor?

    What is the difference between a boost inductor and a flyback inductor?
  7. G

    Measuring Inductance Value of Handmade Inductor

    Hi all! I tried to make an inductor. Naturally, I am not sure about it's inductance value. I made an LC series circuit on a bread board. I am using a oscilloscope and an a function generator to find the value of L during the resonant frequency. Channel one goes from function generator...
  8. O

    Opening switch on inductor circuit in absolute vacuum

    So, a professor in class a about a year ago mentioned that opening a switch in a circuit that an inductor is providing power to would cause a breakdown in the air and a spark would jump across it because the current can't change instantaneously to zero in an inductor. Something just made me...
  9. N

    Inductor sizing and it energy handling ability (SMPS related)

    Homework Statement I am struggled by a problem encountered in studying SMPS, on reading the book 'Switching Power Supply A-Z', for a passage talking about the effect of increase in load current of a DC-DC converter on the inductor size, from the ripple factor formula, r=(delta I)/I_L...
  10. T

    Inductor and electromagnetic field with voltage

    I'm having hard time understanding how exactly current that passes through inductor transforms energy into magnetic field and then into voltage, with 90° phase shift. I drew schemes representing sinusoidal imput current, its magnetic field and voltage relation. Is it correct? Would...
  11. ¡

    Inductor Antenna for 125kHz NFMIC System: FCC Part 15

    I am building a 125kHz Near-Field Magnetic Induction Communication system and so will be using ferrite cored inductors for the transmitter and receiver. I am worried about RF radiation as it pertains to the conformance of FCC part 15. I haven't been able to get any good info on how an...
  12. M

    Current through a single inductor

    Homework Statement Ok, so this isn't a question of how to solve, but rather why the solution works. Say you have a circuit with 2 inductors in parallel, a 5H and a 20H, in parallel to the inductors is a resistive network with a resistance of 8Ω, and a switch, which has been closed long...
  13. madmike159

    Inductor/ Magnetic feild question.

    Homework Statement There is a pic of a L shaped coil (2 L's facing each other but one is upside down). Air gap = 1 mm Turns = 200 current = 2A perm of material = 4000 (relative) I have found the reluctance by drawing a magenitic circuit diagram and i got 41003 which I've been told was right...
  14. C

    Given I, find V across the elements (resistor, inductor, and capacitor)

    Homework Statement The current after t=0 in a single circuit element is as shown in Fig. 2-37. Find the voltage across the element at t=6.5\mu s, if the element is (a) 10 k\Omega, (b) 15 mH, (c) 0.3 nF with Q(0)=0. Ans. (a) 25 V; (b) -75 V; (c) 81.3 V...
  15. M

    Engineering Current through an Inductor in an RL circuit

    Homework Statement Find i0(t) see attached pictureHomework Equations io(t) = iinfinite + (i0- - iinfinite)e-Rt/L The Attempt at a Solution I first re-drew the diagram for when the switch has NOT been closed, which is esssentially the same thing without the 37.5 V Source and the adjacent 10...
  16. S

    Manifesting inductor behaviour

    Hi, The following circuit is the the very basic form of an Hbridge inverter driving a parallel LC tank at its resonance frequency 200khz. The Inductors L1 and L2 are put in series between the square wave output of the Hbridge and the parallel resonance LC tank now I have the following three...
  17. S

    MOSFET output current limited by Inductor Saturation current?

    So the MOSFET's output current in a simple buck converter with a PWm a driver and a MOSFET and LC circuit. The Inductor's saturation or Irms current limits the MOSFET's current output, correct? I heard that if it exceeds saturation current that the MOSFETs could be damaged. is this true...
  18. T

    Op-Amp w/ Inductor: vO & vS Relationship

    Alright, so I have a problem on my homework set that features an Operational Amplifier. It's very similar to a "Integrator" Circuit which means the gain would be.. K = -1 / R*C. The problem is, the capacitor has been replaced by an inductor. I'm trying to find the relationship between vO and vS...
  19. P

    Voltage amplitudes across inductor and resistor

    Homework Statement A series combination of a 22.0 mH inductor and a 145.0 ohm resistor are connected across the output terminal of an ac generator with peak voltage 1.2 kV. (a) At f= 1250 Hz, what are the voltage amplitudes across the inductor and across the resistor? (b) Do the voltage...
  20. C

    Finding the inductor value with a frequency range

    Homework Statement A television channel is assigned the frequency range 53.2 to 57.2 MHz. A series RLC tuning circuit in a TV receiver resonates in the middle of this frequency range. The circuit uses a 15.8 pF capacitor. What is the value of the inductor (in mH)? Homework Equations...
  21. E

    Total electric field within an inductor

    Hi. I have just started learning about inductors, and this is the method my book uses to show that Kirchhoff's second law is still valid even with inductors in a circuit, and to calculate the voltage drop across an inductor: "According to Kirchhoff's loop rule, the algebraic sum of the...
  22. S

    Inductor Doubt: Instantaneous EMF=Back EMF?

    Doubt on Inductor!pleasez help Imagine an AC source and a pure inductor...if the Instantaneous EMF=Back EMF due to changing Magnetic field in Inductor then how does the current flow?
  23. B

    Stored Magnetic Energy - Inductor Circuit

    Homework Statement In the above circuit, the EMF from the battery is 12 V and the resistor has a resistance is 6.6 Ω. The inductor consists of a long, thin cylindrical coil of wire with 30000 turns, a radius of 5 cm and a length of 61 cm. Answer the following questions for a time 1.4...
  24. H

    Calculate max voltage of toggled inductor

    I have an inductor of 500uH that is attached to a 1volt source and the other side is connected to a mosfet RDSon = 0.012 ohm. If I turn on the mosfet for 5us and let current start to flow through the inductor I can calculate the max current reached assuming the current ramps up linearly. Then...
  25. T

    Inductor and Capacitor at different frequencies

    Homework Statement When a particular inductor and capacitor are connected across the same AC voltage, the current in the inductor is higher than in the capacitor. Is this true for all frequencies? Homework Equations Current through a capacitor Ip=(Vp)(2pi)(f)(C) Current through an inductor...
  26. B

    Engineering RL Circuit - Problem finding Unknown Inductor

    Here is the circuit: http://img840.imageshack.us/f/60205514.png/ I need to find: I Z VL - Voltage on Inductor XL L I have I and Z but I can not figure out VL, XL, and L. This is what I have for I and Z: ----------------------------------------------- a.)...
  27. B

    Why does current lag behind voltage in inductor?

    I've seen that this question has been asked but never answered because guy was silent on formulas. I can say that i am familiar with formulas, and i know how to derive the equation for current, and that II/2 lag, but here is the thing... Why? i know that formulas say so... But can someone...
  28. C

    Determining the Optimal Thickness for a 30mH-Solenoid Inductor

    Homework Statement hi, i just have few questions on how to make a 30mH-inductor (solenoid). I have an enameled copper wire which i will wrapped into a 7-inch rebar having 12mm diameter. In order to determine the number of turns, i made some calculations:Homework Equations L=(uAN^2)/dThe Attempt...
  29. C

    EMI - voltage across Inductor

    Homework Statement suppose there is a inductor connected to a battery and resistor in series ... i need to find the current in circuit at some time t i suppose i could use Kirchhoff's loop law but i don't know weather to take potential across inductor (L di/dt) as positive or negative. i...
  30. C

    Inductor spark quenching time.

    hi i saw this page, http://sound.westhost.com/clocks/spark-q.html and he has tried various methods to quench the EMF spark from inductors. when a lot of current is pulled from the inductor during the quench the inductor magnetic field is prolonged - what is this delay called? this is the only...
  31. S

    How does the voltage on the inductor change over time?

    Homework Statement An alternating current is running through a serially connected inductor(L) and resistor(R). The alternating voltage causing it is: http://upload.wikimedia.org/math/5/a/0/5a0ecaa1432c6cdce653a943b4962a21.png How does the voltage on the inductor change over time? Homework...
  32. P

    Capacitor and inductor problem

    Dear All I am struggling with 2 different problems with the basic concept of inductance and capacitance. 1) Firstly, I am not sure if I am understanding correctly how (hypothetically) an initially "charged" inductor can sustain, when short circuited, a constant current. I am right in...
  33. M

    Find the rate of change of the current in the inductor

    Homework Statement For the circuit shown in Fig. 7, what is the rate of change of the current in the inductor when the current in the battery is 0.50 A? (1) 600 A/s (2) 400 A/s (3) 200 A/s (4) 800 A/s (5) 500 A/s Homework Equations i(t)=Imax(1-e-tR/L) induced emf = L (dI/dt)...
  34. S

    The energy stored in an inductor

    I knew the textbook says the inductor store energy in magnetic field. The typical way they demonstrate this is by setting up a circuit, where a battery is parallel connected to a light bulb and an inductor. At the beginning, the light bulb lights up. Then the battery is cut off and the light...
  35. L

    Engineering Voltage/Current of inductor and capactiors 2nd order circuits

    http://www.ece.ubc.ca/~shahriar/eece251_notes/eece251_assignment6.pdf Question 4 on the link. I understand why the top inductor to the left has i = 0A but I don't understand why it has a voltage of 3.816V, can anyone care to explain?
  36. A

    Inductor voltage calculation in time.

    Homework Statement This image gives all variables. Homework Equations Lets say that until second 1 the circuit was as it is. And and from 1 to 5 sec switch turned up, then from 5-6 turned down. Help me to calculate inductor voltage at these time intervals. Please explain to me how...
  37. O

    Resistance of a capacitor and inductor in a dc circuit

    Homework Statement From my Basic DC electronics text. 2 questions, multiple choice, but I seem to be able to talk myself into several of the options. I've combed the book thoroughly, and humbly come to you folks in sincere desperation. The resistance of an/a Inductor/Capacitor in a DC...
  38. B

    Self Resonant Freq of Spiral Inductor

    Is there a model for determining the self resonant frequency of a flat spiral inductor? I can determine the inductance but the capacitance is escaping me. Thanks for any help.
  39. H

    (Magnetic Coupling) Why connect the capacitor in parallel to the inductor?

    I attach below the picture showing the principle of magnetic coupling in witricity (source: Electrons Unplugged by David Schneider, IEEE Spectrum, May 2010). I'm wondering why they connect the capacitor in parallel with the inductor. Why not in series? Any opinion? Thank you :smile:
  40. S

    Energy in inductor and capacitor

    Energy in inductor is given as (Li2])/2 but energy is power absorbed in t secs is E=integral(from 0 to t)Lidi here i is current. since this integral stretches from 0 to t After doing the integral the current i must be turned into the time variable i.e E=(Lt2)/2; Then why are we writing it...
  41. I_am_learning

    Inductor Concept: Voltage, Current & Flux Phase Relationships

    Consider a simple circuit of Real inductor exited by sinusoidal Source. What is getting me into trouble is this. 1. What is the current through the inductor? Isn't it the same as that of resister,which is \phi phase lagging with the applied voltage. (Current is same in a series branch)...
  42. P

    Can an Inductor hold a charge?

    I understand that in an ideal world, an inductor will not hold a charge (when not connected to a circuit). Ideally, there would need to be a current through the inductor to generate a B-field to store energy. I once read, that (since this is not an ideal world), an inductor actually CAN and...
  43. A

    L, E and i: 50.0mH Inductor and 24.0V AC Voltage Source

    A 50.0mh inductor is connected to an ac voltage source of 24.0V.The current flowing in this circuit is 0.60A.The frequency of the voltage source is : a)50Hz b)60Hz c)1.27*10^3 Hz My Work so far ! : f = w/2pi. But here we have L , E and i. Any help will be welcomed.
  44. C

    Core loss calculation - inductor

    can i solve for core loss of a cylindrical inductor by knowing the dimensions of it and the material it is made of?
  45. V

    Circuit with 2 resistors, inductor, and capacitor

    Homework Statement [PLAIN]http://img534.imageshack.us/img534/228/helps.png I have trouble completing (b), as I do not know how to solve for the damping factor in this circuit, and hence cannot characterize this system. I have the poles of the system, where s ~= -3048.059 and s~= -8201.941...
  46. H

    Measuring the frequency-dependency of the resistance of a coil inductor

    0. Bit o' background + greeting Hello everyone. I am a third-year math/physics/CS/AI major and I've never used this forum before, as can be seen from my impressive post count. I enjoy leafing through it though and find myself perpetually impressed by the activity and commitment of the community...
  47. S

    Potential Difference Across an Inductor in an RLC circuit

    Homework Statement An alternating source drives a series RLC circuit with an emf amplitude of 6.0V, at a phase angle of +30deg. When the potential difference across the capacitor reaches its maximum positive value of +5.00V, what is the potential difference across the inductor? Homework...
  48. S

    Resistor or Inductor: Exploring Rheostats

    Hi! A little food for thought for people who like high school physics labs.. In a standard rheostat(I have seen only the cylindrical one..the question is about rheostats of this shape..), we find a metal wire wound over a cylindrical core. The wire is wound with very closely spaced turns...
  49. S

    How Do You Calculate Energy Delivered to an Inductor Over Time?

    Homework Statement the current through an element is i = 2t^2 - 1 Amps. if that element is a 4H inductor, what is the energy delivered to it from time t=1 to t=3. Homework Equations energy in an inductor is dw = Li di The Attempt at a Solution i = 2t^2 - 1 di = 4t dt w = L...
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