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. Z

    Induced Current Due to a Solenoid

    Homework Statement An aluminum ring of radius 5.00 cm and resistance 3.00 × 10–4 Ω is placed on top of a long air-core solenoid with 1 000 turns per meter and radius 3.00 cm. Over the area of the end of the solenoid, assume that the axial component of the field produced by the solenoid is half...
  2. T

    How to determine the direction of induced current in a solenoid?

    I have come across this problem, who to determine the direction of induced current. It keeps me wondering why the answer that i got is Fleming's right hand rule? Aren't it should be Right hand grip rule? Cz the usual and conventional way of inducing electricity in a solenoid is to pass the...
  3. O

    Can a Multi-Position Solenoid be Created with a Permanent Magnet Core?

    Hi- I'm trying to build a simple linear motion control using a solenoid. I've replaced the typical steel core for a permanent magnet core so that I can both push the armature out and pull it back in by flipping polarity (and without using any springs). This works nicely. Unfortunately, it still...
  4. F

    Build a 3000psi Solenoid with 28swg Copper Wire

    Hi, First post, and this stuff is way above my head so i am hoping some one can help me. So what I am after, i am after building a solenoid to to open a valve, this valve is holding back around 3000psi compressed air. its from a pressure washer gun. and takes quiet abit of force to open...
  5. Z

    Confused about solenoid radius from this site

    So I was reading a thread on PF talking about the radius of a solenoid and Bob S answered with a link: On that site, it states that the Radius = the outer radius - the inner. It doesn't make sense. What happens when there is only one layer of coil and the outer radius (OR) is basically the...
  6. B

    How Does Moving an Iron Rod Affect Ammeter Readings in a Solenoid Circuit?

    Homework Statement A solenoid with a large number of turns of wire is connected in series with an ammeter and a battery. An iron rod is moved towards the solenoid at constant speed. What will happen to the reading on the ammeter (A) as the rod moves closer to the solenoid, before...
  7. U

    A coil of wire is placed along the axis of a solenoid?

    http://img42.imageshack.us/img42/6336/14vu.png please explain your answer! also if u know of similar problems or where this problem is taken from do tell me coz i have an admission exam coming up soon please explain the following: 1. what is the flux like? 3. how the coil spins? z. how is...
  8. E

    Equation of a Magnetic Field of a Solenoid

    I'm a Physics student currently working on some research with my advisor. My advisor doesn't know much about modeling solenoids so I've been tasked with reaching outside for help. I did that, but I can't remember the formula or the guy's name so I'm turning to you guys for help. There is some...
  9. O

    What is the contribution of magnetic fields from individual loops in a solenoid?

    I'm a bit confused with the equation for a long solenoid. The usual derivation has us consider a rectangular loop enclosing N number of currents over the length L through it. So by Ampere's law one gets B=μNI/L. The currents and the loop look like this right? --------- | . . . . |...
  10. M

    Energy density of magnetic field in a solenoid

    Homework Statement A solenoid that is 117 cm long has a cross-sectional area of 20.0 cm2. There are 1010 turns of wire carrying a current of 9.56 A. (a) Calculate the energy density of the magnetic field inside the solenoid. (b) Find the total energy in joules stored in the magnetic field...
  11. F

    Electric Field of a Solenoid

    Homework Statement A long solenoid of radius R, length L (which is much longer than R), number of windings N, has a current I that is changing in time at a rate (dI/dt). What is the magnitude of the electric eld a distance R=2 from the axis of the solenoid? Homework Equations...
  12. M

    Under what conditions is a current generated w/ a magnet and solenoid?

    Homework Statement When putting a magnet into a solenoid, under what conditions is a current generated? The Attempt at a Solution In order for a current to be generated, the magnet needed to be moving as it passed through the solenoid. This is due to Faraday’s law, which states that an...
  13. F

    Magnetic and Electric Field outside Solenoid

    Hi, I've seen a couple of posts in the Homework section of Physics Forums about the fields of solenoids, but neither of them seem to address the problem that I have about it. The set-up is a long solenoid that has a sinusoidally varying current going through it. We can establish that the...
  14. E

    Calculating on-axis elements of a solenoid

    I wanted to mention that this solenoid has many winds over many layers. The thickness of the windings is 2.4 inches coming off of the engineering schematics, and has many many many turns, which is unknown. It has a 6T field at the zeroth point on-axis. I'm doing research with a professor and...
  15. E

    Model Solenoid: Best Method & Troubleshooting

    What would be the best method to model a solenoid? I tried writing a program that calculated the off axis elements of the solenoid but the value came out wrong. Any idea?
  16. D

    Magnetic Energy of Solenoid With/Without Core

    I have a question about solenoids. The formula for the magnetic field energy density is: \frac{1}{2}\frac{B^{2}}{μ} If I have an air-filled core, then μ=μ0. If I have a steel core, then μ will be ~ 100μ0. This implies that an air-filled core solenoid stores more energy than a steel core...
  17. A

    Inductance of Solenoid on Coaxial Cable

    Homework Statement The figure below shows a short coil which is coaxial with a very long solenoid (you may approximate it as infinite.) Coil: Has 120 turns of radius 1.8 cm and resistance 5.8 . It is not attached to anything. Solenoid: Has 22700 turns/m and a radius of 1.6 cm. It receives an...
  18. Z

    Faraday effect in glass cell within solenoid

    Homework Statement Describe the Faraday effect as it might be observed in a glass cell contained within a solenoid Homework Equations The Attempt at a Solution When a glass cell is immersed in a strong magnetic field, the plane of vibration of light waves is rotated. When...
  19. C

    B field inside solenoid as a result of iron rod

    Homework Statement Consider a solenoid with a time varying current and with a coil of wire placed around it. Suppose there is a soft iron rod inside the solenoid. My question is: What happens to the (induced) current in the coil of wire as a result? Homework Equations Faraday, magnetic...
  20. D

    Conceptual Questions Lenz's Law, Solenoid

    Homework Statement https://www.dropbox.com/s/17hsoz0zdfoston/Screen%20shot%202013-05-10%20at%2012.37.44%20PM.png 1) A voltage is applied to a solenoid such that a current is flowing in the indicated direction. Inside the solenoid is a single wire loop that is oriented in the same...
  21. E

    What are my option to power a pneumatic solenoid? on a timer

    Hi guys. This is for an engr project that I am involved in. I have everything else worked out but this got me stomped. I've been searching for a while and can't find something that fits my application. basically the solenoid is controlling a dual acting air pneumatic cylinder. the solenoid...
  22. W

    Increasing number of turns in a Solenoid?

    Hello! I understand that by increasing the number turns the magnetic field is strengthened. But would that "extra" turns demand more power input from the power source?
  23. J

    Why is the magnetic field inside an ideal solenoid uniform

    I understand that the magnetic field at points inside the solenoid is the vector sum of the B field due to each ring. How can the field inside be uniform then since if you consider just one loop in the solenoid the value of the B field is different at different points in that circle or loop.
  24. P

    Magnetic field created by a solenoid

    Homework Statement Inside a very long, straight and hollow plastic tube (R << L) we have ionized liquid moving at a velocity v = 100 m/s. The net charge per unit volume is n = 106 electrons/m3. The radius of the tube is R = 10cm. Around the tube we have a solenoid, with n = 100 loops/m...
  25. warrenchu000

    Difference between a solenoid and a stack of loops

    The B field at the center of a stack of N circular loops each carrying current I is B = mu0 * N * I / (2a) where a is the radius of the loop, derived using Biot-Savart law. The B field inside a solenoid is B = mu0 * N * I / l where l is the length of the solenoid, derived using Ampere's...
  26. F

    Make Solenoid Work: Tips for DIY Coil Winding

    I wound 4 layers on a piece of 3/4 conduit. The wire is 20 gauge (.032) and the coil length is 7 inches. I put 5 amperes into the coil and a bolt that fits the conduit didn't move. It stuck to one side of the conduit but it didn't snap in as I expected. What do I do to make this solenoid work?
  27. K

    How do I calculate the necessary force for my solenoid and return spring?

    So I'm building a solenoid that needs to move a load of 5 ounces, 0.4 inches. I'm pretty sure my calculations for the force inside the coil on a iron pin are correct: F = (B^2 * A) / (2 * Uo). Where B is the flux density, A is cross sectional area of pin Uo is permeability of free space...
  28. A

    Induced Current for a Solenoid Pulled Away From Loop

    Homework Statement Sorry for the blurry picture. If the coil is being pulled away from the loop shown to the right, in what direction is the current induced in the loop? Homework Equations right-hand rulesThe Attempt at a Solution I assumed it to be clockwise just from looking at the...
  29. L

    Looking for equation/proof of b field in a solenoid

    Hi guys, I'm looking for an equation and/or proof of the magnetic field produced inside a solenoid with a finite length (hence, it shouldn't just be "muNOT n I." For some reason I can't find a simple proof anywhere. I have no idea where to start. ampere's law obviously doesn't work, and that...
  30. T

    Time-varying magnetic field outside a solenoid

    something that has had me confused: How can I calculate the time varying magnetic field produced by a solenoid, outside the solenoid along the axis of the core. I know that: inside the solenoid : apply amperes law For DC (magnetostatic) case outside the solenoid : apply Biot-savart law...
  31. R

    Determine Current in a Solenoid

    Homework Statement As a new electrical technician, you are designing a large solenoid to produce a uniform 0.170 T magnetic field near the center of the solenoid. You have enough wire for 4200 circular turns. This solenoid must have a length of 1.10 m and a diameter of 1.50 cm. What current...
  32. C

    Magnetic field in a solenoid due to induced current in a coil

    Homework Statement A coil of wire with N turns is placed around the a long solenoid with n turns per unit length carrying a current I as shown below, A)If a current I flows through the solenoid, derive an expression for the magnetic flux through the coil and explain why the size and shape...
  33. J

    Solenoid & Lenz's Law: Choosing Option B

    I know that the answer will not be a or c due to effects of gravity. But I can't decide between b and d. I chose b because of lenzs law. I thought that since the south pole enter first, there will be an increasing flux upwards, coil opposes this by inducing an magnetic flux downwards. When it...
  34. T

    Current and Voltage of Elements of a Circuit with a Solenoid.

    Ended up figuring out how to solve this problem. I just was not expecting certain parts of the results which lead me to believe I did it wrong.Homework Statement Voltage of battery is 5V Resistors are 5 Ohms The solenoid has no internal resistance 1.Need to find V_2 before switch is opened...
  35. K

    Calculating Force on a Solenoid Plunger

    I'm trying to figure out how to calculate the actual physical force on a solenoid plunger. I.E what kind of load it can pull or push. So if I setup a magnetic circuit and calculate the flux going through it at maximum airgap, am I right to assume that the force is equal (B^2 * A) / (2*u)...
  36. R

    Calculating the magnetic field in solenoid

    Just need a question cleared up. If I had a coil wrapped around a core, and I was calculating the magnetic field of the solenoid using B = μnI where n = N/L, I is current and μ is the permeability of my material N being the number of turns in the coil, and L being the length of the...
  37. M

    Does a Conical End Affect the Magnetic Field Strength of a Solenoid?

    If instead of a disc shaped end I have a conical end , would there be any change in the measured magnetic field strength at the end of the solenoid keeping current, core and number of turns per unit length constant ?
  38. S

    Log expansion for infinite solenoid

    Hello, I found an approximation for this log function: log \Bigg(\frac{\Lambda}{\rho} + \sqrt{1 + \frac{\Lambda^2}{\rho^2}} \Bigg), where \Lambda \rightarrow \infty . The above is approximated to the following, -log \bigg(\frac{\rho}{\rho_o} \bigg) + log \bigg(\frac{2 \Lambda}{\rho_o}...
  39. A

    : solenoid and superconductor questions

    URGENT: solenoid and superconductor questions Sorry I cross posted this, but I realized that general physics was probably a better place for it... I have a few questions regarding the levitation of a piece of superconductor using the field from a solenoid. In other words, I want to calculate...
  40. X

    How to determine the leakage flux around a solenoid

    Hey everyone, I am currently attempting to determing the leakage flux (for all intents and purposes) from a solenoid (DC current) with various core shapes and sizes. I have tried doing this using Comsol and Feko, but so far have been unable to. Does anyone have any knowledge of either of these...
  41. S

    Attraction of a steel rod with a solenoid

    Homework Statement From this video: http://www.youtube.com/watch?feature=player_detailpage&v=mdZo_keUoEs#t=77s it shows that the steel rod will eventually stay in the middle of the solenoid. At first the magnetic field of the solenoid would look like...
  42. jaumzaum

    Magnetic field far from a solenoid

    I know the magnetic field inside the solenoid is μIn/L and outside is 0 (provided that the point is near the solenoid). But if we had a long solenoid and choose a point far from the solenoid (and perpendicular to it), would it behave like a wire? Would the magnetic field be μI/2πR?
  43. joe_cool2

    Does Solenoid Diameter Affect Acceleration of a Metal BB?

    Homework Statement We're given two solenoids with identical currents and turns per unit length. But the solenoids have different diameters. Would a metal BB experience a larger acceleration in the smaller diameter tube, assuming we use the same BB in both solenoids it accelerates along the...
  44. F

    Magnetic field of iron core solenoid

    When we calculate magnetic field of iron core solenoid, should we multiply "relative permeability" or "effective permeability"? I thought that we should use relative permeability, but wiki(http://en.wikipedia.org/wiki/Solenoid) says that we should use effective permeability. I'm so...
  45. R

    Induced electric field in a solenoid

    Homework Statement A long solenoid with 1000 turns per meter and radius 2cm carries an oscillating current given by (5A)\sin(100\pi t). What is the electric field induced at radius r=1cm from the axis of the solenoid? What is the direction of this electric field when the current is...
  46. R

    Very long solenoid ampere law paradox?

    Hello I have been doing some thinking related to Ampere law and behaviour of magnetic field inside materials of different permeability. In the process, I came up with the following thought experiment: Try imagining a very long solenoid with steady current I. Turns of the solenoid are...
  47. J

    Finding B-Field Of Solenoid Slightly Off Axis?

    If you have a solenoid positioned along the z axis... ...how would one find the b-field at slight deviations of x and y? I have been googling for hours and can't find anything other than the fact that it is very difficult! Thanks guys!
  48. E

    E field induced by toroidal solenoid with changing current

    Homework Statement Suppose we have a toroidal solenoid with square cross section and whose axis of symmetry lies along the z axis. Suppose a current I(t)=kt runs through the solenoid. Find the induced electric field at an arbitrary point on the z axis. Homework Equations \oint \vec E \cdot...
  49. Z

    Measuring magnetic field in a solenoid

    I have to measure the magnetic field created by a solenoid. My attempt would be using a commercial Axial Hall Probe, or a Hall Sensor with some electronics. It has got an active (sensing) area with a diameter <1 mm. My coil is 12 mm long and has an inner diameter of 9 mm-s. My problem is that...
  50. larrybud

    What size linear solenoid do I need for a tennis ball launcher?

    Hi all, I'm building a tennis ball launcher for my dogs, and was successful in building a spring loaded one with a "whacker bar" that rotated on a pin. A wiper motor turned the bar until the bar got to the half way point around the pivot, then the spring would pull the bar, hit the ball, and...
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