# What is Magnetic circuit: Definition and 41 Discussions

A magnetic circuit is made up of one or more closed loop paths containing a magnetic flux. The flux is usually generated by permanent magnets or electromagnets and confined to the path by magnetic cores consisting of ferromagnetic materials like iron, although there may be air gaps or other materials in the path. Magnetic circuits are employed to efficiently channel magnetic fields in many devices such as electric motors, generators, transformers, relays, lifting electromagnets, SQUIDs, galvanometers, and magnetic recording heads.
The law relating magnetic flux, magnetomotive force, and magnetic reluctance in an unsaturated magnetic circuit, Hopkinson's law bears a superficial resemblance to Ohm's law in electrical circuits, resulting in a one-to-one correspondence between properties of a magnetic circuit and an analogous electric circuit. Using this concept the magnetic fields of complex devices such as transformers can be quickly solved using the methods and techniques developed for electrical circuits.
Some examples of magnetic circuits are:

horseshoe magnet with iron keeper (low-reluctance circuit)
horseshoe magnet with no keeper (high-reluctance circuit)
electric motor (variable-reluctance circuit)
some types of pickup cartridge (variable-reluctance circuits)

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1. ### I Calculation for proportional mechanical solenoid Force

I'm looking for calculation for proportional solenoid force (constant force for some working stroke) using magnetic reluctance based on equivalent magnetic circuit by networking method. I was reading a book Elektromangnate by Dr Kallenbach which discussed such method but for switching solenoid...
2. ### Help! Finding Direction of Current in Magnetic Circuit

I have nearly finished my homework, but am blocking at one of the simplest questions... I'm going to let ##\rho=0.094\,\Omega/m## Since the magnetic flux is increasing, then, by Lenz's law, the current in both loops is counter-clockwise. If we only look at the left loop, then...
3. ### How to determine the number of turns of the winding?

1) B = Φ/S = (4.2*10^(-3) Wb)/(2.5*10^(-3) m^2) = 1.68 T 2) Using electrical steel magnetization curve given in the textbook: magnetic field strength H corresponding to magnetic flux density 1.68 T is equal to 6000 A/m. 3) L is a length of the middle magnetic line of the core (Fig. 2). L =...
4. ### Engineering Find the parameters in a magnetic circuit (ignore the leakage effects)

That was my attempt , but I am not sure if my answer is correct or not . I want to confirm it .
5. ### Engineering Determine the shunt field current in a magnetic circuit

Problem Statement : Here's my attempt : * By assuming that the fringing and leakage effects are ignored. I find the flux density , the permeability and the reluctance of the iron , but then I get stuck . Any help would be greatly appreciated .
6. ### Checking My Understanding of a Magnetic Circuit: Help Appreciated!

So I was checking this question out, and I saw that someone did discuss about a similar question before on this forum here: https://www.physicsforums.com/threads/did-i-get-it-right-by-coincidence.487088/ Since this is a different question, I would like to ask if anyone here could help me check...
7. ### H-field and MMF in a magnetic circuit

I have been revising magnetic circuits concepts and I think I am missing something regarding H-field and mmf. If the 100-turn primary of a transformer is energized with 1A dc, its mmf will be 100A-T. And all the line integrals H.dl enclosing the primary coil will equal 100A. As per magnetic...
8. ### Faraday's law or Lorenzt force?

A student in my physics class posted, in a group, a wrong answer to a question. The situation was: A plane has a wire extended between the tips of its wings and flies through a magnetic field, perpendicularly, while accelerating. The question was: What will be the induced current? His answer...
9. ### How the reluctance in a magnetic circuit depends on flux?

Since reluctance is equal to length decided by product of permeability and area of cross section,how does reluctance change with flux?
10. ### Engineering Finding required coil current (magnetic circuit)

Homework Statement Toroidal core N = 1000 turns R = 6cm r = 1cm established a total flux of 0.0002 Wb in a non-magnetic core. Find the required coil current
11. ### I What is Reluctance in a Magnetic Circuit?

Electrical resistance is due to electrons colliding with the atoms of the conductor. In a magnetic circuit reluctance is analogous to resistance in an electric circuit. Just as resistance impedes the flow of electrons in an electric circuit, reluctance impedes the flux in a magnetic circuit but...
12. ### Engineering Deriving the circuit approximation of a magnetic circuit

Homework Statement For the magnetic circuit: Derive the circuit approximation. Compute all magnetic fluxes if the total solenoid current is I. Homework Equations Rm = L / μS The Attempt at a Solution [/B] Mostly, right now, I'm just trying to determine the magnetic circuit equivalent. From...
13. ### Calculate mean path length of a magnetic circuit

Given this magnetic circuit: With these dimensions: With this equivalent circuit: If I am using F = HL to calculate the mmf drops in RcoreAB(see equivalent circuit) and RcoreBCDA(see equivalent circuit) then how would I calculate L in the formula ?
14. ### Engineering Optimize the design of a magnetic circuit actuator

Homework Statement The aim is to optimize this actuator to get the maximum force from it. Here is the circuit diagram below: Homework EquationsThe Attempt at a Solution Length of air gap top (Ragt in diagram) = 0.5 mm Length of air gap centre (Ragc) = 0.25 mm Current in coil = 0.8 A (I...
15. ### Engineering How to Calculate Reluctance and Estimate Force in a DC Electromagnetic Actuator

Homework Statement Consider the DC electromagnetic actuator shown in Figure 1 which is constructed using Hotrolled Silicon Steel laminations. All dimensions shown are in millimeters. For this actuator0.5 mm diameter Copper wire is used for the winding, the bobbin has a thickness of 5 mm, the...
16. ### Question about transformer reflected source

The following show the idea how a Thevenin equivalent source is used to replace the primary circuit of transformer. https://www.dropbox.com/s/0kaazx1d1srgirz/reflectedsource.jpg?dl=0 https://www.dropbox.com/s/0kaazx1d1srgirz/reflectedsource.jpg?dl=0 In textbook it is commonly stated that the...
17. ### Understanding MMF in Transformer

I am studying about transformer and get confused about some concept. I have learn that in an ideal simple transformer the primary has two components of current: Magnetization current i.e. the open-secondary primary current. Current that (ignoring small leakage inductances) finds it way (via...
18. ### Ampere's law and magnetic circuit

For magnetic circuit there is an equation NI=HL. This equation is obtained by applying Ampere's law. H is magnetic field intensity and L is the length of the circuit. In following picture the equation reduced to I=HL as there is only one turn...
19. ### Permeability in ferromagnetic material (AC)

Homework Statement The following coil-wound core (core length = L , Gap length = lg, cross- sectional area = A , core permeability = only hysteresis graph is given, N = N turns) is driven by a Voltage source, is known that the current in the coil is 60hz AC. Determine...
20. ### Calculating the magnetic field of a closed magnetic circuit

I am interested in calculating the magnetic field strength produced by an electromagnet with a core shaped like an O that forms a closed magnetic circuit, shown in the attached image that can also be seen here -...
21. ### Slab Beam of electrons through Neutralising Ions

Homework Statement A slab beam of electrons of thickness a, width w >> a, charge density (-ρb ), (Take ρb to be positive.) and velocity vbez passes through a channel of neutralizing ions with charge density f*ρb where f is some number between zero and one (all parameters given above apply in...
22. ### LittleBits - magnetic circuit board

I was doing some online early-ish Christmas shopping for the kiddo and wife-o. I randomly came across this: http://littlebits.cc/ I thought it was pretty cool, and I figured some people here would appreciate it too :). (For those who don't wish to click on the link, it's basically magnetic...
23. ### Response time of a magnetic circuit and its elements

This one is for people working with electromagnets (more specific, DC) etc. I have a few questions that I am struggling with: I am quite comfortable with the concept of the response time (time constant) of a coil in free space, μ0 =4π x 10-7 . The thing I am struggling with is the response time...
24. ### Material Property Effects On Magnetic Circuit

I'm building a linear actuator and I don't have much experience with magnetic circuits... A rough sketch of what I'm building is attached. I'm trying to determine if the materials I'm using for the shaft and shaft collar will have a detrimental effect on overall force output. Right now, my...
25. ### Engineering Series parallel magnetic circuit

Homework Statement The attached figure shows a magnetic series parallel circuit with an air gap, what I'm not sure of is how to add the individual reluctances of the core and air gap to get the total reluctance required to calculate the current. Homework Equations The Attempt at a...
26. ### Engineering Flux density in magnetic circuit

Homework Statement Consider the magnetic circuit shown in figure 3 Assuming that the core (μr=1000) has a uniform cross section of 4 cm^2, determine the flux density in the air gap the picture is very small so here are the values L=42cm, Ig=0.1cm, turns=500, and I=0.2A Homework Equations...
27. ### Engineering EE: Mutual Inductances in Magnetic Circuit

Homework Statement The symmetric magnetic circuit has three windings. Winding A and B each have N turns and are wound on the two bottom legs of the core. The core dimensions are indicated in the figure. b.) Find the mutual inductances between the three pairs of windings. figure ...
28. ### Question about magnetic circuit

recently I am working on magnetic solenoid and got a question. The attachment shows the simple cross-section. Blue green represents the steel providing the magnetic flux path and red is the copper wire with current flowing into the screen. Also, the whole structure is in cylindrical shape...
29. ### Engineering How to Calculate RMS Current and Voltage in an AC Magnetic Circuit?

the question is; if there only a current in coil a, and it is AC, calculate the rms current required in coil a to maintain an alternating flux in core section a with a peak value of 1.2T calculate the rm voltages at the two coil terminals if coil resistances are neglected (attached in...
30. ### Inductance in a magnetic circuit

Homework Statement I have a magnetic circuit with a coil wrapped around the centre "leg" of the core as follows. I have been given average lengths, areas and permeabilities for the three legs and the airgap. Homework Equations L = (N^2*µ*A)/l The Attempt at a Solution For the...
31. ### Engineering Magnetic Circuit Homework: Get Help with Unseen Questions

Homework Statement Refer attachment q.Homework Equations Refer attachment f.The Attempt at a Solution Refer attachment t. Please help, this lecturer likes to give questions that are not taught during exams.
32. ### Numerical model of simple magnetic circuit

Homework Statement I have to build a 2D model of simple magnetic circuit, that is iron core (2) with coil(1) and air gap(3) applied to it. Model has to be solved on numerical basis, by finite difference or element method (whichever is easier to implement). Number 4 on drawing represents...
33. ### Can mechanical shock enhance the flux through a magnetic circuit?

Dear geniuses, I'm planning on working with a magnetic circuit that consists of several bars of low carbon steel magnetically "powered" by two NIB permanent magnets. The steel bars are 1 inch square in cross section and so are the two magnets. When completed, the entire circuit forms a...
34. ### Can Permanent Magnets Achieve 10,000 Gauss in Cyclotron Magnetic Circuits?

For a cyclotron application, I want to make a magnetic circuit using permanent magnets. The attachment shows a diagram of the circuit. It has two neodymium magnets "in series" and mild steel bars extend to duct the circuit around to two disk shaped pole pieces (red and blue). The diagram is...
35. ### Engineering How Does Plunger Shape and Permeability Affect Magnetic Flux Density?

Homework Statement The magnetic circuit consists of a core, a movable plunger of length lp, permeability mu, area Ac and mean length lC. the overlap area is the function of x, Ag = Ac(1- (x/xO)) Neglect fringing. (Also in the figure for simpler calculations I have assumed lp= g) a) For...
36. ### Lorentz Force in Magnetic Circuit Air Gap

http://en.wikipedia.org/wiki/File:Magnetischer_Kreis.svg The attached image shows a magnetic circuit with a small air gap. The magnetic material on each side of the gap is attracted to the other side. I've seen the magnitude of the force calculated based on principle of virtual work...
37. ### What could be causing unexpected results in my magnetic circuit?

Hello, I have designed a magnetic circuit.. C core with an air gap. I calculated the circuit as well as doing a simulation on it using FEMM software. The core is from 1018 steel. My calculation and simulation gave almost similar result.. So, there is no problem in my calculation or...
38. ### Magnetic Circuit Problem Involving a Solenoid and Plunger

Homework Statement The problem can be found http://whites.sdsmt.edu/classes/ee382/homework/382Homework1.pdf" (the last one), along with a picture of the circuit. Homework Equations R = l/(µS) mmf = NI = ΨR B = Ψ/S The Attempt at a Solution I've never done a problem like this...
39. ### Magnetic Circuit with diferent section

Homework Statement Given the following magnetic circuit: It's constituted by two cores in serie. The first one has an average length of 40 cm and the second of 10 cm. Both are made of ferromagnetic material, which can be considered lineal and with \mur1 = 1000 for the first one, and \mur2...
40. ### How Can I Build an Effective Magnetic Separator for a Mineral Factory?

Hello, I am looking for a paper that explains how to build a magnetic separator. This separator will be used in a mineral factory over a conveyor belt and the ferromagnetic particles are at least 0.5 Kg weight. I also know that i have to place the rectangular magnets inside a iron "box" but i...
41. ### Engineering Magnetic circuit for Saturable reactor

I have a problem that has a common core and two wound coils. The core is square with sides A and D opposite and C and B opposite. Side A and D have the same cross sectional area and side C & B have the same cross sectional area. Sides C and B have the coil around them. I know the current in...