Talk:Solenoid

Lines of force acting in the wrong direction?

I suspect that, on the second image down on the right ('Magnetic field created by a seven-loop solenoid') the arrows on the magnetic lines of force are shown pointing in the wrong direction. By convention lines of magnetic force emanate from the north pole which, by the right hand grip rule, is on the left of the solenoid.

Also suggest that the image would be improved by showing the north and south poles.CPES (talk) 15:27, 19 December 2016 (UTC)

No, it's correct - although the "dart" notation for current flow might be unfamiliar. Andy Dingley (talk) 15:46, 19 December 2016 (UTC)

Yes, you are correct. I am familiar with the dart notation- I was having one of those days! Thanks CPES (talk) 09:37, 23 December 2016 (UTC)

The Selenoid page should be added to the Inductor page.

Solenoid vs Inductor ?.

In physics, the term refers to a coil which produces a uniform magnetic field when an electric current is passed through it. A solenoid can be more specifically classified as an inductor rather than an electromagnet. Not all electromagnets and inductors are solenoids.

If you would like more technical Proof in form of Facts, Then please let me know.

Contributed by. GCHQ MI6 ULTRA (Signal Intelligence).

GCHQ-Mi-6 (talk) 21:13, 28 June 2017 (UTC)

The solenoid article includes a link to the inductor article. The inductor article includes a link to the solenoid article. If that's what you mean by "the Selenoid page should be added to the Inductor page" — then it's already done. - LuckyLouie (talk) 01:07, 29 June 2017 (UTC)

Should remove equations

While nukephysik101.files.wordpress.com/2011/07/finite-length-solenoid-potential-and-field.pdf isn't spam, I don't think we can justify whitelisting it in because it's not a WP:RS in the first place. A lot of the other material is unsourced, and I've already seen transcription errors on this page in the past. I think the best thing to do would be to remove the equations and point the readers to reliable external sources like Cylindrical Magnets and Ideal Solenoids for now, until/unless someone wants to rewrite from reliable sources. Rolf H Nelson (talk) 23:29, 6 January 2018 (UTC)

Understandability, variety, and what's not a solenoid

While parts of the whole article can be understood by people with limited education, there's significant content that is highly terhnical. Imho, the whole article seems to require major editing and rearrangement.

Typical solenoids are commonplace, and easily understood; the abstruse theoretical aspects and discussion belong in their own section.

The introduction is far too academic. Much better would be a few good photos of widely–used solenoid actuators, including their sliding cores. Cores should be shown separate as well as installed, in both energized and de–energized positions. At least one photo should show the coil without its protective cover, to reveal the magnet wire winding.

Most practical solenoids include ferromagnetic surrounds ("cores") of varying sophistication; solenoids without cores are far less common in practice, except in radio receivers of the early 20th century.

Functioning solenoids are easy to make, given a source of magnet wire, although "hookup" wire surely will work, but with lower packing density. Moreover, if film–insulated magnet wire is used in a classroom, try hard to obtain green insulation! Plainly–visible insulation is mandatory, imho.

Single–layer windings are atypical, beloved by academicians, being amenable to analysis, but rare in practice. So–called scramble wound coils are practical, and work very well.

The term "solenoid" is applied specifically to a) academic helices (not flat spirals, such as in induction food cookers) and b) electromagnetic actuators, nearly all of which have the coil and its magnetic circuit mounted on the frame of the device which uses them.

Other wirewound electromagnetic devices are conventionally not called solenoids, such as focus coils for CRTs that use magnetic focus, transformers, toroidal and other inductors, analog pointer meters, et cetera.

Must confess that I've not read all, yet, but TV camera tubes, vidicons and image orthicons, have surrounding focus coils that extend nearly or actually over the entire length of the tube. These coils are solenoids, and the uniformity of the magnetic fields inside such coils is crucial to their operation. This type of electron optics differs from that in which focusing fields are more local with respect to the overall size of the device, such as magnetic–focus CRTs. In "immersion" magnetic focus, where the coil extends along the device, electrons move helically between sources and destinations.

Helmholtz coils are not conventionally considered to be solenoids, nor are rigid ("hard") disk drive actuators.

While loudspeaker and headphone/earphone coils are much like academic solenoids (but with adjacent turns in contact), they're not typically referred to as solenoids.

(Query, for the academicians: What effect does "tightness/looseness" of turn spacing have on inductance and possibly other parameters? Early radio coils (inductors) had adjacent turns in contact, tightest–possible turns spacing. It seems that turns spacing of academic solenoids is always (?) "loose", or am I missing something?)

Somewhat off–topic, but electromagnetic actuators tend to fall into two different types: Those in which magnetic attraction* dominates, and those in which orthogonal force dominates, such as loudspeaker voice coils and disk head actuators.

• Or, more rarely, repulsion

Solenoids without ferromagnetic flux paths, "air core", also pull their moving cores into their centers, but with miserable inefficiency. They develop force by what could be considered a third means, in which the theoretical loops of magnetic fields act like elastomers—rubber bands— developing force by what could be considered contracting forces, minimizing path length outside the solenoid.

Btw, feel free to use text here without attribution.

I discovered a really annoying bug while proofreading this, using Android 10. Trying to edit near the beginning repeatedly snapped focus to the end of the text!

By user nikevich Nikevich 02:43, 27 December 2021 (UTC)

After posting this, I went ahead and edited the first section (only). In retrospect, I think maybe I should restrict myself to copy edits, not major ones. At age 85, I could be "losing my touch". user:nikevich.Nikevich 05:13, 27 December 2021 (UTC)

Needs more practical explanation and examples

This article is probably great for academic use learning about solenoid theory, but is difficult to read to find out practical information on solenoids, similar to what Nikevich states above.

The term solenoid is also often used to mean a mechanical actuator consisting of a coil of wire with ferromagnetic armature that is attracted inside the coil when the coil is energised.

Bidirectional solenoids as electromechanical actuators are also produced using 2 separate coils, such that one coil attracts the iron armature in one direction and the other coil attracts the armature in the other direction.

I am an engineer and I just wanted to look up practical engineering information about mechanical actuator solenoids. I.e. how many turns are needed to create a given force and displacement of a given size iron core with specified magnetic susceptibility.

Early telephone loudspeakers used a moving iron core inside a solenoid.

A solenoid is also used as part of a moving coil loudspeaker. The solenoid coil is held in a magnetic field and as it is energised with the alternating current of the audio signal, the coil will move in one direction or the other depending on the audio signal polarity. The coil is part of the diaphragm arrangement which is in turn held by a flexible sprung surround, such that with no signal the coil and diaphragm will return to the central position. The movement of the diaphragm will depend on the force which can be applied by the magnetism from the coil against the permanent magnetic field, balanced by the force of the flexible spring mounting and force applied to move the air.

I would expect that bidirectional electromechanical actuators could be made with a movable magnet inside a solenoid coil, similar to the way a loudspeaker works.

Solenoids are also used as part of magnetic locks/latches. A permanent magnet incorporates a solenoid coil, such that when not energised a ferromagnetic plate or bar will be held with a force which cannot be overcome within the scenario of use. When the solenoid is energised, it produces an opposite magnetic field counteracting the force of the permanent magnet, such that the lock can be opened.

Etc.

Lkingscott (talk) 11:10, 5 December 2023 (UTC)

This is precisely what I came here to say. Thank you! Adamtakvam (talk) 07:33, 27 December 2023 (UTC)