What is Inductor: Definition and 455 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. E

    What explains the current flow in a LC circuit?

    I'm just not able to grasp the concept of a LC circuit intuitively, and yet I have found zero answers to my doubts. I can't understand why does the current keeps flowing counter-clockwise between the 3rd and the 4th circuit (see image attached) I know that when the capacitor has 0 charge, in...
  2. L

    Introduce a battery to an LR circuit

    Let's say I have an LR circuit. I understand the mathematical derivation of this but would like to understand it conceptually. Okay, so a battery is introduced (let's say 12 V). The inductor hates the change, so it induces 12 V in the opposite direction, opposing the battery. So what happens...
  3. S

    B LC resonance with high Q factor, Inductor with non magnetic core

    Consider Inductor with air gap and solid metal core made from material with relative magnetic permeability 1 regardless of temperature (such as copper or aluminium). There is Air gap between coil and metal core Please Also consider Eddy currents in the solid metal core. The Inductor is...
  4. A

    Engineering Short vs Open Circuit: Is That Correct?

    For the first circuit, Req = ZL + ZC = -j/(w*C) + j*w*L = 0 for short circuit, so w = 0? For the open circuit case, -j/(w*C) + j*w*L = infinity, so w = infinity? Is that correct?
  5. J

    Trying to analyze a half wave rectifier with inductor and DC source

    I am trying to analyze a half wave rectifier with an inductor and DC source load. I understand the circuit but I guess I do not get the math. I am reading a book and this is the circuit and equations they came up with. I understand how they got from the first equation to the second equation but...
  6. W

    Electronics Would This Setup for a Ball Bearing Accelerator Work?

    I need a method to accelerate a ball bearing down a pair of wire tracks, and to generate a consistent amount of force on every activation. Please critique my tentative design: I want to use an inductive coil activated by a proximity sensor to generate a transient EM field to accelerate the ball...
  7. W

    Advantages of Circular vs Cylindrical Inductor Core?

    All the inductor components I’ve see are made with a circular core instead of a cylindrical core. Are there any advantages to this design in terms of field strength relative to input current (assuming the same number of turns of wire)? In the field strength equation, is “coil length” always...
  8. abdulbadii

    I Outright understanding L/R inductor time constant

    How is the real understanding, when an external constant E potential (voltage) is imposed/applied on a LR circuit, that is being charged as the characteristic L/R inductor time constant: the greater R the shorter time inductor get (full) charged This absolutely independent to the E; it could...
  9. S

    Exploring Inductor Design for Audio Applications

    Hi, I am experimenting with a design for an inductor for audio applications, and am using a high permiability toroid (12,000) having a closed trifilar winding. In this instance , it is 39T x 3 twisted wires connected in series being 117 turns in total, giving approx 180mH inductance. In...
  10. J

    I How does a ferromagnet increase the inductance of an inductor?

    Inductance according to Faraday's law depends on a changing magnetic field. The magnitude of the induced emf depends on the magnitude of change in the magnetic field per change in time. Based on that, how does adding a constant magnetic field (a ferromagnet), increase the inductance of an inductor?
  11. J

    I Does an inductor always create a back EMF?

    Let’s use a solenoid for example. Let’s say you have a current that passes through a solenoid clockwise. Due to Faraday’s law of induction, the induced current from the magnetic field from an increasing current opposes the initial direction of current causing resistance. If the initial current...
  12. J

    Find the inductance of an inductor in a circuit

    When the current has been running for a while we can treat the circuit connected to e like a battery with two resistors. The current at this point is 2.5 A so using kirchhoff's loop rule we find that the emf of the battery is 2V. $$\varepsilon - IR - IR = 0$$ When the switch flips to f, we can...
  13. A

    I Inductor questions (generate a voltage opposing the source voltage?)

    1) Why does there have to be an inductor to generate a voltage opposing the source voltage? Doesn't the circuit create back voltage without an inductor? 2) In ##U = \frac{1}{2}LI^2 + \frac{1}{2}\frac{Q^2}{C}## ##E = \frac{1}{2}mv^2 + \frac{1}{2}kx^2## where ##x(t) = Acos(wt + \phi)## following...
  14. MadelineChoate

    Toroidal Inductor Flux Calculation

    Summary:: A 4.3 mH toroidal inductor has 100 identical equally spaced coils. If it carries an 11.6 A current, how much magnetic flux passes through each of its coils? Express your answers in milliwebers. 4.3 mH= (Wb/A) 100= N 11.6= I Φcoil= ? So from my observation of another question...
  15. E

    Total current needs to go through the inductor L1, How ?

    Summary:: So the question is, what do I need to do on clamp 'ab', so that the total current only goes through the Inductor L1. I know the must be a second inductor parallel to the capacitor C1, but i don't know why. Can someone please explain. I also included the german question under the picture.
  16. V

    B Why does an inductor discharge?

    A capacitor will discharge because once a path is created there is a potential difference $V=Q/C$. But for an inductor it's $L\frac{di}{dt}$. Why would an inductor want to discharge once you connect it to a capacitor?
  17. PhysicsTest

    Inductor voltages and currents

    I have redrawn the circuit as below 40 - (I2+0.5)200 - (I2 + IL)*300 = 0 -> eq1 -(I2 + IL)*300 - IL*280 - 4*dIL/dt = 0 -> eq2 Are my equations correct?
  18. PhysicsTest

    Inductor Circuit Simulation: Understanding Current Rise and Voltage Output

    I am trying to understanding the inductor circuit. I have drawn the below circuit and try to simulate The Inductor current comes to 500mA and Vout is 5V as per simulation. The current in inductor should slowly increase from 0A to 500mA but i cannot see that in the waveform. Is my understanding...
  19. A

    Inductor Efficiency via LC Oscillator

    I want to create an LC circuit with varying inductors and compare those inductors for efficiency. Would it be accurate to suggest measuring the area under the curve of the first cycle of the resonant frequency would determine which of the inductors are most efficient? If the area is greater...
  20. T

    Measuring time constant using an inductor with a core vs. no core

    I'm doing a simple RL Circuit Lab where students use 800- and 1600-turn air core coils to measure the time constant. Experimental results very nicely agree with predicted results. However, when students insert a steel (or iron) core in the coils, experimental results are far different than...
  21. awen

    Using an inductor choke as a receiving antenna for LW radio

    Hello, I'm interested in using a choke inductor as a receiving antenna for long-wave radio signals (300kHz). What are the "obstacles" in comparison with a standard ferrite rod antenna used in AM radios? So far I'm registering these: 1) low Q at the desired frequency available chokes seem to...
  22. H

    The Direction and magnitude of current in the inductor

    I understand that the current is going rightward because of the negative sign in the equation above, but why is the current increasing not decreasing? The current doesn't stay constant because it changes with the time based upon the equation above again.
  23. PhysicsTest

    Understanding Inductor Behavior When Transistors Are Off

    a. When the transistors are ON. ##V_{CC} = V_L## ##V_{CC} = L \frac{di_L} {dt} ## ##i_L = \frac{V_{CC}t} L ## b. I am bit confused when the transistor is "OFF" The point "A" is floating? The transistors and the diodes all the elements seem to be open is it correct? I am confused here.
  24. Truman I

    Potential Drop Across 15-mH Inductor at t=0?

    At t=0, I believe that the current is instantaneously 0 Amps. If that is correct, then technically at that instant there is no voltage drop across any of the resistors due to Ohm's Law. So I replaced the resistors with wire. Next, I tried replacing all of the capacitors with open circuits to...
  25. PhysicsTest

    Peak energy stored in inductor

    The figure is as shown below a. From 0< t < t1 => 0 <t<4ms, the transistor is "ON" The circuit will become like this The current ##i_s = i_L##. To know the magnitude of the current ##i_L## do i need to know the impedance of the inductance or since it is DC voltage the impedance is not...
  26. X

    Engineering Find di(0+)/dt and dv(0+)/dt of circuit containing resistor, inductor

    Dear PF, I am trying to solve practice problem 8.1 and I am stuck on part b which asks us to find di(0+)/dt and dv(0+)/dt. Down below in the picture is my attempt. Before t=0 it is quite intuitive since the inductor acts as short circuit to steady-state DC and a capacitor acts as open circuit...
  27. S

    Calculating the current in an inductor (AC)

    I integrated the second equation given in the form (integral)di= 1/L * (integral) V *dt and I got an answer of 3.52 for the current at 0.4 seconds, anyone can let me know if this is correct?
  28. E

    Voltage across an inductor after flipping a switch

    When the energy of the capacitor is minimal it has no charge therefore the voltage on it is 0. That means that the voltage on the inductor is 0 as well at the moment. The part that confuses me is: why isn't the correct answer 0? How can a voltage change in a single moment? Furthermore I am...
  29. G

    DC Inductor for an Arc Welder Conversion

    Hello, I want to make a choke for a AC to DC welder conversion. The welder is a 50hz single phase oil cooled unit with constant current output upto 110A. I will bridge rectify the output to give rectified AC output. I need to smooth the output and as I need a constant current output, I'll...
  30. halleff

    Physical/conceptual reason for inductor voltage step response

    I'm trying to understand the physical reason why when you drive an ideal inductor (no series resistance) with an ideal voltage step input (no series resistance), e.g. some Vin(t) = V0u(t), the output current will be a linear ramp. I can see how to derive this from the inductor equation, v = L...
  31. mcastillo356

    Demo of the I-V equation of an inductor

    Hello, I would like to know the demonstration of i-v formula ##v=L\dfrac{di}{dt}##. Does it come from Faraday's law, ##\epsilon=-N\dfrac{\Delta{\phi}}{\Delta{t}}##?; why does sometimes appears ##v=-L\dfrac{di}{dt}##? . Magnetic flow in a constant magnetic field, ##\phi=BA\cos{\theta}## is also a...
  32. mcastillo356

    What are the implications of considering infinite first derivatives in circuits?

    Hi I've attached the image of the circuit. My first thought before connecting it: if I connect it, I must consider the fact that current cannot circulate suddenly, because a sudden change in the amount of current should imply an infinite value in \dfrac{\Delta{I}}{\Delta{t}}, and a infinite...
  33. D

    Voltage and current as functions of time for a series RL circuit

    I already found ##I(t)## using Kirchhoff's laws, I got the equation ##V-RI-L\frac{dI}{dt}=0\Rightarrow L\frac{dI}{dt}=V-RI## then I solved the differential equation getting ##I(t)=\frac{V}{R}\left[1-e^{-\frac{R}{L}t}\right]##. My problem is founding the voltage as a function of time ##V(t)##, I...
  34. M

    Engineering AC circuit: Find the current through the inductor & capacitor

    Hi! I wonder if it is correct. Can someone confirm (maybe with a software) ? I(L) = I2 I(C) = I2 - I3 -- Thanks.
  35. J

    How does the current divide in parallel inductors?

    I apologize using English fluently because I am not an Enlgish speaker. When I tried to solve this problem, I used current divider rule. So, $$i_o(t) = \frac{3}{3+5}*4e^{-2t} = 1.5*e^{-2t} A$$ However, This was wrong. The answer is $$ 1.5*e^{-2t} + 0.5 A$$ If I use $$V_O = L*\frac{di}{dt}$$...
  36. fight_club_alum

    Why Does an Inductor Store Energy After No Current?

    I calculated all the required in this problem correctly but can't understand why the sum of energy extracted and absorbed is not zero. They are: >0: 0J 0 <=E<=25: 4t^2 J 25 <= E <= 50: 4t^2 - 0.4t + 10 * 10^-3t J E > 50: 0 J Does that mean that an inductor stores energy even after there...
  37. tesla58

    Solve Confusing Inductor Question: Finding Parts b,c,d - Help Needed

    Summary: Confusing Inductor question I've been in trouble with a question for whole days , trouble is finding parts b,c and d. ------ in the solving of part b WHEN we find i0(t) ,why minus is in front of integral(-1/4 coefficient one) and why +5 why not -5 ? I think it relates passive...
  38. fight_club_alum

    Inductor Efficiency: Does it Produce More Current?

    Hey everyone, I am taking a circuit 1 course in college and was wondering if an inductor is actually efficient. What I mean is that does it produce more current than the current already supplied. I know it keeps the circuit going even after the voltage source is cut, but does that mean that, if...
  39. engnrshyckh

    Power supplied by a Capacitor and Inductor

    Using above eq Xc=80.38Ohm and P=179VAR but textbook says that the ans is zero. Can anyone explain please
  40. harsh22902

    Flux & Physics: Explaining the Constancy of Flux

    This is an excerpt from a high school physics textbook. I don't understand the possible reason behind this statement. If we change something in the circuit say for example add a resistor , the current and hence the flux should change. Then why/how is this statement true?
  41. asadahmad_7869

    How to find the charge at time = t (at any instant)

    I was not able to derive the charge on the capacitor. But then, I arbitrarily assumed ##\phi=B.A## (Dot product of Magnetic field and Area) Then, proceeding as follows, ##\phi=BA\cos(\omega_0 t)## ##\frac{d\phi}{dt}=−BA\omega_0\sin(\omega_0 t)## Now at ##t=0, \phi=BA\cos(0)=BA## Therefore...
  42. D

    Planning to measure voltage (back EMF) caused by opening a switch in series with an inductor

    i am planning to measure the back emf produced by inductor when you open a switch. i know it is very hard to predict the voltage. but is there any way to narrow the possibilities?
  43. J

    Multi-Tapped Toroidal Inductor questions

    Hi, The thing is that i want to wind a multi-tapped toroid inductor for the this circuit (see picture at the bottom) Using an MPP core. What i am confused about is this. On the following table you can see that when the permeability of an MPP core increases the high frequencies it can handle...
  44. J

    Winding a toroid inductor, is this calculation correct?

    Hi, I am going to wind an tapped toroid inductor for a LCR circuit in an equalizer. I have calculated the number of turns I need for each winding. This is my first time winding an inductor so I need to get some things straight. What to do with the 10 kHz tap, should I twist a wire with the 12...
  45. A

    Rectified Current Through an Inductor

    Hello, I need to find the magnetomotive force (mmf) of an inductor using NI (turns multiplied by amperes). The set up is pretty simple, AC power supply set at 24 VAC goes through a full wave rectifier (4 diodes) and into an inductor. If the inductor has a resistance of 47 Ohms, it looks like...
  46. C

    Lightning Protection System w/ Inductor: Impact?

    If there's an inductor in series between a lightning rod and the ground rod, how will it affect the lightning protection ability of the system?
  47. Tesladude

    What is the voltage across this capacitor, inductor and resistor?

    I can solve for the questions in completely series or parallel circuits however having the capacitor and inductor in parallel while the resistor stays in series is stumping me completely.
  48. Zack K

    How exactly do inductors work in an LC circuit?

    I understand Faraday's law and about induced electric fields created by a changing magnetic fields, etc. But what causes the current to oscillate in an LC circuit, with no battery? If you picture that there is current going into an inductor, and that current is decreasing over time, then you...
  49. N

    Deriving Voltage from the Inductor Equation

    Homework Statement L = 20mH = 20 x 10-3 H i = 40 mA for t≤0 i = A1e-10,000t + A2e-40,000t A for t≥0 The voltage at t=0 is 28 V. I have to find the equation for the voltage for t>0. Then I have to find the time when power is zero. Homework Equations v(t) = L* di/dt p(t) = L*i* di/dt The...
  50. M

    Question about Intuition of Inductor

    Homework Statement I am trying to figure out how an inductor works in depth. It should be something very simple to find, but I have yet to find an explanation that goes through the process step-by-step in a non-circular way. I can solve the inductor differential equations and do phasor...