What is Inductors: Definition and 132 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. M

    When do inductors act like a short circuit and when they dont?

    -My professor said that if i is constant through an inductor that V=0 through the formula V=L(dv/dt) . So if an inductor is in series with a voltage source it will act like a short circuit. But if the inductor is in series with a resistor and the voltage source the inductor will not act like a...
  2. U

    Power dissipation in inductors

    I have found a possible mistake in my book...here's the text which contains it, "Referring to figure, it can be seen that no power is disspated in a pure inductor. In the first quarter of cycle, both V and I are positive so the power is positive, which means that energy is supplied to the...
  3. B

    A thought experiment involving inductors

    I have a theoretical question involving the properties of inductors, I hope someone is able to help! I know that the voltage across an inductor is proportional to the time rate of change of the current through the inductor, and that if the current is changed the inductor will generate a...
  4. S

    Do Inductors Share Energy in the Same Way as Capacitors?

    When an uncharged capacitor is connected to a charged capacitor there is a loss in energy due to radiation (the calculation is in the attachment "inductors_share_energy", after the inductor sharing energy calculation to this message). When a current carrying inductor(shorted on itself) is...
  5. A

    Discrepancy bet. maxwell + circuit notation w/ inductors?

    Well... Consider a basic RL circuit. Maxwell tells us that the induced EMF=-L dI/dt. The voltage drop across the resistor is of course RI, but why does this mean that RI =L dI/dt as every physics textbook says. That statement relies on the fact that path integral around the circuit is = 0...
  6. T

    Engineering Help with a circuit (inductors)

    Homework Statement The voltage across an L = 2.5mH inductor is v(t) = 10 cos(1000t)mV, with i(0) = 1 mA. (a) Find i(t) for t ≥ 0. (b) Find the power and energy.Homework Equations V= L * di/dt Power= V * i V * i= L * i * (di/dt) The Attempt at a Solution I really don't know where to start...
  7. I

    Engineering Magnetically coupled inductors an AC circuits

    Homework Statement I've actually uploaded the question. When solving problems with magnetically coupled inductors I like to add dependent sources so that I can keep everything straight. My question is when I add the dependent sources does there need to be a specific polarity to them. With...
  8. Pythagorean

    Inductors and 'path of least resistance'

    Why is the wire in an inductor not insulated from the other turns in the wire? Or rather, why isn't it necessary? We learn that the electricity will take the path of least resistance, so why would it bother going around each turn when it can just skim straight across the inductor and leave...
  9. P

    Inductors: DC vs AC Current for Buyers

    I'm looking to buy some inductors, axial or radial ones. What I need to know is the difference between measured dc current and ac current. Modeled in multisim, the max dc current through the inductor is about 1mA but the max ac current approaches 1A. I know inductors have max current values, so...
  10. P

    Inductors for Colpitts Design AM Transmitter

    I'm trying to design a AM transmitter using a colpitts design. I see many different types of inductors available for sale, smt, torrid, dip, ferrite core, iron core, etc... Which one should I buy? I know they have different Q values and max current. What do you think the max current would be for...
  11. I

    Problem with inductors and Capacitors in Series (AC Theroy)

    Homework Statement Find the steady state expresion for i(t) in the circuit if Vs=750 Cos(5000t) mV All componets are in series Resitor = 400 Ohms Inductor = 40mH Cap = .4 \muF Homework Equations Xc= 1/(j*w*C) Xl = j*w*L Xr = R The Attempt at a Solution Ok I know...
  12. A

    Do all objects have inductive properties?

    I'm not entirely sure if this post belongs here, but I guess the topic of electrodynamics is vast. My question is; are there any materials / plants / animals that act as electric inductors? In other words, are inductors solely made up of coiled wires, or do they occur naturally? To...
  13. H

    How do I determine the energy stored in an inductor after 2 seconds?

    Homework Statement A resistor R is connected in series with an inductor L. The battery is connected at time t = 0. How much of this energy after 2 seconds is stored in the magnetic field of the inductor? Homework Equations U_{L}=\frac{1}{2}Li^{2} i(t)=i_{0}(1-e^{\frac{-t}{\tau}})...
  14. A

    Energy stored in the magnetic field of two inductors

    Homework Statement Two solenoids on the same cylindrical axis Solenoid A has 400 loops and a current of 3,5 amp. Produces a flux of 300microWb on itself and 90 microWb on solenoid B Solenoid B has 700 loopsHomework Equations Calculate the energy stored in the system.The Attempt at a Solution...
  15. G

    Calculate Leqv for Parallel Inductors

    Diagram shown in attachment. Two inductors having self-inductance L1 and L2 are connected in parallel. The mutual inductance beween the two inductors is M. Determine the equivalent self-inductance Leqv for the system. I'm pretty much stuck on this one. Since the current splits off and...
  16. W

    Circuit with Inductor: Current, Battery, Resistor

    The problem is: There is a circuit such that a battery (source of constant emf) is connected to an inductor and a resister (in series). After an unspecified time period, a switch is thrown, effectively bypassing the battery. I know (becuase I've seen the answer) that a) the initial current...
  17. J

    Solve the Circuit: Find v(t) Over Inductors

    Homework Statement http://img134.imageshack.us/img134/8382/circujitqt7.th.jpg i0(0) = 10 A i1(0) = 20 A The currents through the inductors flow from top to bottom. And v(t) is + on top and - on bottom Homework Equations The Attempt at a Solution Find the voltage v(t) over both inductors...
  18. F

    Inductors with apparent negative inductive reactance?

    1. I am currently progressing through my assignment, however I have been given a circuit with 2 values of Z: Z1 has a magnitude of 30 and angle of -31. Z2 has a real value of -12 and an imaginary number of -36. 2. When these are both converted to complex number format: Z1 = 25.715 -...
  19. cepheid

    What is the difference between voltage across an inductor and back emf?

    I thought I understood inductance. It's sort of an inertial property in circuits. Physically, it accounts for the fact that "it takes work to do stuff", meaning that if you put a voltage across a coil of wire, the current through that coil can't jump up to whatever steady state value it will...
  20. C

    Capacitors and Inductors values

    So being fresh from school, a lot of times as students we dealt with unrealistic values for caps and inductors. I remember doing a textbook problem where a cap's value was 1 F. Now that I'm in the real world. What is considered to be a realistic value? To push the question further, I see a lot...
  21. P

    How Do Inductors and Capacitors Operate in AC/DC Circuits?

    My knowledge on how inductors and capacitors operate in AC/DC is a bit shaky. My textbook and online material don't help my understanding, so I am hoping someone would be able to explain it more clearly. In DC I know that capacitors store energy and charge up by time constants and then...
  22. V

    Solving Impedance/Admittance for V_s w/ 2 Caps, 2 Inductors, 2 Res.

    Impedance and Admittance: Find Vs given Io in a circuit with 2 caps,2 inductors,2res Homework Statement Find V_s if I_0\,=\,2\angle0\deg A. http://img237.imageshack.us/img237/6291/problem954zz0.jpg Homework Equations KCL, KVL The Attempt at a Solution I made a new diagram...
  23. V

    General SEcond Order Circuit: 2 Res. - 2 Inductors - Current Source

    Homework Statement Obtain i_1 and i_2 for t > 0 in the circuit below. http://img258.imageshack.us/img258/7765/problem60as1.jpg Homework Equations V_L\,=\,\frac{di_L}{dt} The Attempt at a Solution To get initial conditions, I made a second circuit diagram for t < 0...
  24. J

    Why does the back emf effect increase with frequency?

    Hi, If I remember correctly, if one applies an alternating voltage across an inductor then the back emf produced by the inductor increases with the frequency of the voltage. However when I decrease the frequency of the voltage to less than 100hz and I plot a trace of voltage against time...
  25. K

    Inductors: what do they do?

    I've been studying circuits for almost 3 months now, and I can pretty much carry out analysis of circuits with inductors. I know the basic relationships for an R-L circuit etc, how to derive the equations and so on. In other words, I can solve textbook problems. But what does an inductor...
  26. E

    Exploring Inductors in Electro-Magnetic Circuits

    one more electro-magnetic question: here's the set-up: two inductors, the A-B has a signal source hooked-up, C-D is open circuit. ->i1 A C ) ( + ) ( V2 ) ( - B D i1 is given as a triangular wave, v2 as a step wave for: 0 < t < 0.5, i1 has negative...
  27. E

    Zin(s) of magnetically coupled inductors

    I am not quite getting how this works: i have a serially connected two inductors L1 and La (primary) and a secondary circuit with also two inductors (L2 and Lb), the problem asks to find input impedance in s-domain. The answer given is s[La + L1 - M2/(L2 + Lb)] so, could someone explain how...
  28. M

    Using inductors to reduce electric bill?

    Using inductors to reduce electric bill?? My professor today mentioned that if you place an inductor in one of the power outlets in your house will allow actually produce no power and will cause your electric bill to reduce since that specific outlet is causing the power meter to reverse its...
  29. B

    Laplace Transforms and non ideal inductors

    Hi there, I'm trying to derive an expression for the transient response (for a step input of magnitude V), for a non-ideal inductor modeled in the schematic I have drawn. This non-ideal inductor includes its inductance ( :smile: ), a parasitic parallel resistance and a parasitic capacitance...
  30. B

    I don't understand what inductors do

    Hi! Here is probably a simple problem but I can't solve it: We have an inductor (just a coiled wire) in series with a light bulb, connected to an ideal battery. The light bulb is shining and we measure the intensity of light. Now we introduce a metal piece inside the coil. AFTER the piece is...
  31. F

    Charging of Inductors: Explained Without the Duality

    Most people understand (gut understanding) the charging of capacitors more than that of inductors. They just apply the duality to inductors and move on (without seeking the same understanding of inductors). Teachers of my past never could explain exactly why the charging of a capacitor...
  32. I

    Inductors i think it'll make an harmonic type of move

    as far as i know about inductors i think it'll make an harmonic type of move... but it seems to make no sense can anyone help?
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