What is Solenoid: Definition and 743 Discussions

A solenoid (, from the Greek σωληνοειδής sōlēnoeidḗs, "pipe-shaped") is a type of electromagnet, the purpose of which is to generate a controlled magnetic field through a coil wound into a tightly packed helix. The coil can be arranged to produce a uniform magnetic field in a volume of space when an electric current is passed through it. The term solenoid was coined in 1823 by André-Marie Ampère to designate a helical coil.In the study of electromagnetism, a solenoid is a coil whose length is substantially greater than its diameter. The helical coil of a solenoid does not necessarily need to revolve around a straight-line axis; for example, William Sturgeon's electromagnet of 1824 consisted of a solenoid bent into a horseshoe shape.
In engineering, the term may also refer to a variety of transducer devices that convert energy into linear motion. In simple terms, a solenoid converts electrical energy into mechanical work. The term is also often used to refer to a solenoid valve, an integrated device containing an electromechanical solenoid which actuates either a pneumatic or hydraulic valve, or a solenoid switch, which is a specific type of relay that internally uses an electromechanical solenoid to operate an electrical switch; for example, an automobile starter solenoid or linear solenoid. Solenoid bolts, a type of electromechanical locking mechanism, also exist. In electromagnetic technology, a solenoid is an actuator assembly with a sliding ferromagnetic plunger inside the coil. Without power, the plunger extends for part of its length outside the coil; applying power pulls the plunger into the coil. Electromagnets with fixed cores are not considered solenoids.
The term solenoid also refers to any device that converts electrical energy to mechanical energy using a solenoid. The device creates a magnetic field from electric current, and uses the magnetic field to create linear motion.

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  1. Lachlan

    Non-Uniform Magnetic Field Calculations

    TL;DR Summary: Need help with figuring out how (or even if I can) to calculate the magnetic field field strength for this non-uniform magnetic field. I need help calculating the magnetic field strength (if it's possible) in the space between these two solenoids. It is for my year 12 depth...
  2. J

    I Question about Activating Solenoids that are facing each other

    In this situation I would have two solenoids facing each other, such that both ends are north for example, and when activated they are actively experiencing repulsion, I know that the magnetic field of both would decrease in strength, but would there be any affect on the electrical input of each...
  3. Mitchell Richardson

    Finding force between solenoid and magnet

    $$\mu = 4\pi \times 10^{-7}$$ $$n = \frac{180}{0.135} = 1333.33$$ $$I = 1.85$$ $$L = 22.619$$ $$r = 0.014$$ $$F= \frac{\mu \times 1333.33 \times 1.85^{2} \times 22.619}{2 \pi \times 0.014}$$
  4. A

    Flux linked with circular coil vs solenoid

    $$E_{max}=N^2πr^2Bω=N×0.603V$$ $$<E_{avg.}>=<N^2πr^2Bω\sin⁡(ωt)>=E_{max.}<sin⁡(ωt)>=0$$ $$I_{max.}=N×0.0603A$$ Average Power loss=$$\frac{<(E_{ind}^2)>}{R}=N^2×0.018W$$ The correct solutions are : ##0.603## ,##0## ,##0.0603##, ##0.018## Why am I gettting an extra N? Is the emf of thin circular...
  5. M

    B Current-carrying coil and solenoid

    What is the difference between a current-carrying coil and a solenoid?
  6. Grandpa04

    Finding current of circular (toroidal) solenoid

    I assumed that the radius is referring to a major R like in the image below. I plugged all the values (except for length) into the equation B = µ*N*I/2πr to get 155.6 A for the current value. I am unsure if this is the correct value or if radius refers to minor r of solenoid, in which case a...
  7. A

    Modeling an earthing switch for a High Voltage Impulse Generator

    Hi All, I am trying to model this mechanism for a project. It is a switch that uses a solenoid to break the contact by lifting the aluminium arm. I understand that there is most likely software out there that can do this but i would like to understand how to model this from first principals. I...
  8. Hak

    Magnetic field in a solenoid with rectangular cross-sectional area

    I was thinking of using magnetic monopoles, but I don't know how to do. I tried to calculate the magnetic flux through the cross section of the solenoid if a current ##I## flows through it. Magnetic induction inside can be given as ##B = \mu_0 n I##, whereas magnetic induction at a distance...
  9. Hak

    Coaxial semi-infinite solenoid and superconducting disc

    I have no idea how to deal with the problem. Do you have any hints, please?
  10. turo_loler

    I Magnetic field at a point along the solenoid's axis but outside the solenoid

    For a personal project, I need to calculate the EMF induced by a solenoid, the problem is, that the secondary circuit where the eddy currents are formed are outside the solenoid's length but still on it's axis. The problem comes when i need to calculate the vector magnetic field inductance at a...
  11. Szecska8

    I Stored magnetic energy of solenoid

    Can someone explain to me what the second integral represents and what is A?
  12. M

    Electron in a time variable magnetic field

    TL;DR Summary: Find acceleration of electron in dB/dt >0 Hello. Here is a problem that i'm not so sure about: Inside a solenoid there is a time-dipendent magnetic field B, so we have dB/dt = b (constant). We want to know the acceleration of an electron: a) placed in the center of the solenoid...
  13. quarkyphysicsgirl

    Electric field generated by solenoid

    The formula we are given is E=(1/2r)(alpha)R^2(muo)Ioe^-(alpha)t. However, I am struggling to figure out what each of the symbols stands for in the formula...can someone help me out? Like super confused on what alpha is in this case.
  14. C

    Is it possible to build a low-voltage Thompson jumping ring apparatus?

    Hi all, I'm attempting to build a jumping ring apparatus (a core of iron with the bottom wrapped with wiring like an electromagnet, so that when a metal ring is placed on top of the coil and a current is run through the coil, the ring jumps up into the air). Looking on the internet, I'm seeing a...
  15. M

    Electromagnet Polarity Switching for Reversed Motion

    I am trying to understand the differences in design between a traditional solenoid with a ferrous plunger vs linear motors that use either induction or permanent magnets. From my understanding, a traditional solenoid, whether DC or AC, cannot fire in both directions with polarity switching since...
  16. R

    How are the connectors on the DC linear actuator utilized in wiring?

    A am working on a project that uses this 12V DC linear actuator. The actuator utilizes a magnetic coil and plunger inner design (I believe this is just a solenoid). This actuator will need to use both directions of movement for the project. In terms of wiring, what do the two female connectors...
  17. V

    Why are the effects of a magnetized material neglected in this case?

    According to what I know, the net magnetic field ##\vec B## inside a solenoid is given by $$\vec B = \mu_0 \vec H + \mu_0 \vec I$$ where ##\vec B## is the net magnetic field inside a current carrying solenoid, ##\vec H## is the magnetic intensity ( aka magnetic intensity or magnetizing field...
  18. E

    Setting Voltage supply for a solenoid

    I'm currently making a solenoid valve for a home project, I've been testing the solenoid with a DC Lab power supply, I have set the desired 12V but after connecting it drops and I get a high current with a small voltage. I understand that it will only draw the voltage required to push the...
  19. kuruman

    Insights How to Model a Magnet Falling Through a Solenoid

    [url="https://www.physicsforums.com/insights/how-to-model-a-magnet-falling-through-a-solenoid/"]Continue reading...
  20. billyt_

    Drop height of a magnet vs. induced EMF in a solenoid

    I am currently working on an experiment that involves dropping a magnet from varying heights and measuring how the induced emf of a solenoid changes as a result. I am currently somewhat struggling with a derivation for a relationship between the two variables, however, this is what I have been...
  21. B

    Engineering First order differential equations (movement of a rotary solenoid)

    My question i am trying to solve: I have successfully done first order equations before but this one has got me a little stuck. My attempt at the general solution below: $${5} \frac{\text{d}\theta}{\text{d}t}=-6\theta$$ $${5} \frac{\text{d}\theta}{\text{d}t} =\frac{\text{-6}\theta}{5}$$...
  22. M

    Helix Angle or Pitch Angle for this Solenoid carring Current?

    I honestly have such a dumb question- it says “a pitch angle” but cannot find that in relation to a helix. It is not defined in the textbook. Looking on google I found a helix angle, but is that different than the pitch angle? Can anyone draw me a picture of where the pitch angle is? I assumed...
  23. L

    An iron cylinder inside a solenoid

    From ##\oint_{\Gamma}\vec{H}\cdot d\vec{l}=\sum I## by Ampere's Law which gives ##H \Delta l=\Delta N\cdot i\Leftrightarrow H=n i## where ##n=## number of turns per unit length so ##i=\frac{H}{n}=\frac{10^3 A / m}{\frac{200}{0.2m}}=1 A##. Since ##\vec{H}=\frac{\vec{B}-\mu_0\vec{M}}{\mu_0}## we...
  24. J

    Can Resistance Determine the Torque in a Solenoid Pendulum System?

    The flux enclosed by the loop consisting of the solenoid, wires and conducting rod at an angle θ is Φ = blBsinθ, then using small angle approximations and differentiating the induced emf can be found. I know that there must be some torque opposing the motion but am unsure how to proceed.
  25. M

    Amplify ferrite core solenoid electromagnetic range

    Hello all, I'm playing around with a PIC + LCC Tank to send - at a 5MHz frecuency - some numeric data via BPSK. The receiver is a loop antenna placed in the ground. The sender antena (L) is a ferrite core solenoid (N=10). As having a larger core, or increasing the Number of coils around the...
  26. warhammer

    I Guidance Requested on Inductance Formula for Solenoid

    In my textbook on EM, the formula for self inductance of a finite solenoid is given as: L= (μ(o)* N^2*A * {√(a^2+ l^2) - a} )/l^2 where a=Radius of each turn, l=length of solenoid. I am having trouble and extreme difficulty in trying to ascertain how this formula was derived in the book and...
  27. godiswatching_

    What is the effect of a 1 cm gap on the magnetic field in a solenoid?

    Hey, I was trying to figure out this problem. I got (a) using B = mu * NI/L but I'm not sure how to start the part about the magnetic field in the gap after the solenoid is ripped in half with 1 cm gap. Thanks for the help!
  28. P

    Why is magnetic field half at the sides of a solenoid?

    For a solenoid, magnetic field at the centre = ##\mu_0nI##. I see the argument on why at the opening at the ends of the solenoid, the B-field is ##\frac12\mu_0nI##. Apparently, B-field is ##\frac12 \mu_0nI## at the sides of the solenoid too. (ie at/within the wires that make up the solenoid)...
  29. yaxlei

    I Why is an iron cover needed for a solenoid?

    Hi everyone, I've heard that it's better to close the "magnetic circuit" of a solenoid by adding a metal casing around the coils, but I don't get why : people say that it's for focusing the magnetic flux lines but how does it increase the force generated by the solenoid ? Thanks if you reply...
  30. C

    What speed v(t) enables constant power by solenoid pull?

    Assuming the position x = 0 if no air gap, max stroke of plunger is L. Bordery conditions: x(t=0) = L, x(t=T)= 0. Given magnetic force F(x) = kx(t)^-2, here k is constant. If uncontrolled, there is big crash noise afer solenoid actuated, so I wish it pull plunger at constant power. Help me find...
  31. F

    Choosing pneumatic solenoid, AC or DC

    Hi There are mixed information on these on google. I want speed(low lag) first, valves will be open and closed 1-2 minutes. Controlling them with Arduino or ESP with relays. Do I get this right? AC 220 - controlling them with Solid State Relays + Speed of Solenoid with AC is faster than DC +...
  32. L

    Help with linear solenoid calculations (engine valve actuators)

    Hello, thanks in advance, I do many many things, jack of all trades but master of none. Would some one be willing to help me with some formulas and calcs for making my own linear solenoid? I can give the final specs I'm after then I could use advice on materials and other variables. I'd like...
  33. F

    Solenoid wrapped with 2 wires?

    I have a bit of a mystery with a circa 1905 solenoid and not sure where to turn, hoping someone here might have some insight. The particulars Circa 1905 solenoid (application is an electromagnet in a self-winding clock) 8 layers of windings of 2 different cotton sheathed copper wires paper in...
  34. R

    Is the magnetic field inside a solenoid stronger near the border?

    I was reading some papers about calculating the magnetic field produced by a coil using the biot savart law and I saw some graphs that caught my attention. This one from a paper from Ravaud, et al. Titled "Calculation of the Magnetic Field Created by a Thick Coil". I saw similar graphs in...
  35. S

    Potential difference across the ends of a solenoid

    Emf between the center of the disc and its rim = ##- \frac{d \phi}{dt }## = ##-B.A \frac{d \cos (\omega t)}{dt}## =##\mu_0 \frac{N}{L} I A \omega \sin (\omega t)## Potential difference across the ends of the solenoid = ##10\mu_0 \frac{N}{L} I A \omega \sin (\omega t)## Is this correct? How to...
  36. lekh2003

    Electrical How to use capacitors in a Solenoid circuit

    I've been working on designing an experiment over the past few weeks as part of a school project, under the supervision of a teacher. I have designed a small low-power coil-gun. I have a coil of roughly 60m 24 AWG copper wire wrapped around a length of 2.5cm of clear PVC pipe. I tested the...
  37. T

    Field of a Trianglular Solenoid

    No calculators or equations are needed for this question. The correct answer is supposedly "The field is strongest at point Y" and I have no idea why. I even coughed-up the following, but still can't see how this is the right answer.
  38. lelouch_v1

    Magnetic Flux outside of a long solenoid

    I have been reading Griffith's Introduction to Electodynamics and i am currently at the chapter about magnetostatics. There is an example about a long solenoid with n units per length and radius R that shows a way of finding the magnetic vector potential. The magnetic field inside the solenoid...
  39. S

    Correct statement about solenoid

    I imagine the question to be like this: Take x - axis as horizontal and y - axis as vertical so the cross sectional area of the solenoid is parallel to x - y plane, then I take two parallel circles (back to back) to represent "A long solenoid with closely spaced turns". I assume there is...
  40. Y

    Understanding energy conservation in a solenoid

    So let's assume ideal wire, resistance = 0 Ohms. Also assume there is a magnetic ball 1 meter away and is attracted to the solenoid. If you have a loop of wire and run a small current through it, you get a magnetic field. This field attracts the magnetic ball, over a distance of 1 meter. If...
  41. G

    Confusion on the magnitude of magnetic fields

    Here, the correct options are A,D. Solution: I got A as answer as ∫ B.dl=µI. But, the answer to the question says that it is a solenoid and therefore Bx=0 for point P. Here I'm a bit confused. I know this system resembles a solenoid in some ways, then By must have some finite value, but...
  42. kunalvanjare

    PWM for controlling liquid flow through a Solenoid Valve

    Hello guys, I am looking to control the flowrate of water through a Solenoid Valve in a continuous closed-loop process. I inquired about Proportional Flow Solenoid Valves and these are a little too expensive and only a handful of manufacturers are supplying those. But I looked online for some...
  43. S

    { help } Calculating the B-field at the center of a solenoid

    Problem 52: A solenoid is 40 cm long, has a diameter of 3.0 cm, and is wound with 500 turns. If the current through the windings is 4.0 A, what is the magnetic field at a point on the axis of the solenoid that is (a) at the center of the solenoid, (b) 10.0 cm from one end of the solenoid, and...
  44. Adesh

    Calculating the magnetic field of an infinite solenoid

    Here is the image ## \tan \theta _1 = \frac{a}{z} ## ## \tan \theta _2 = \frac{a}{l+z}## where l is the length of the solenoid and z is the distance from the forward center to the point P. My doubt is how ##\theta_1## going to become 0 and ##\theta_2## ##\pi## as the length of solenoid...
  45. J

    Motor/generator solenoid armature

    There are many examples of a 2 pole motor/generator having an armature wound in solenoid fashion, albeit with a steel core. In the limit as the solenoid becomes more perfectly made, long and tightly wound, it would seem not be a good design. An ideal solenoid has zero magnetic field outside...