Talk:Maxwell coil

Would someone provide and validate the field lines for this as in the Helmholtz pictorial.

Image
This article would benefit greatly from an illustration Hotjellysnowman 15:14, 5 March 2007 (UTC)

The picture is incorrect in that the dimensions of radius and separation are switched around (see refs). A new picture, perhaps with field lines as suggested would be of real benefit here. DanielSlaughter (talk) 04:20, 20 February 2008 (UTC)

Article
I've deleted "It can develop magnetic field gradients along the direction of the main field," added by 204.56.7.1. It doesn't make sense. The whole purpose of the device is to eliminate magnetic field gradients as much as possible.--76.81.180.3 (talk) 20:29, 21 November 2007 (UTC)

Major edit, including some references and mention of the two apparently different versions (note the are both mentioned together in Maxwell's original publication). DanielSlaughter (talk) 04:20, 20 February 2008 (UTC)

Unreferenced material in description section.
The description of the Maxwell coil is referenced from a paper written by Maxwell himself.

The description claims that Maxwell specified the ratio of the "ampere-turns [effectively turns if they carry the same current] of each of the smaller coils should be "exactly $$\frac{2}{\sqrt{7}}$$ of the middle coil".

There then follows a discussion that Maxwell's original design was not as good as it could have been in that he should have used all manner of other numbers of turns and in particular, that he should have used 48 turns on the middle coil instead of the 49 specified in his work.

In fact Maxwell's paper never mentions the ratio of the turns of the coils. He simply states that the number of turns on the middle (large) coil is 64 turns and the number on each of the small coils is 49 without ever discussing where the numbers came from. Indeed the ratio $$\frac{2}{\sqrt{7}}$$ is not mentioned at all in connection with the design.

The ratio $$\frac{2}{\sqrt{7}}$$ is unreferenced, and James Clerk Maxwell would have been very unlikely to make such a schoolboy error in calculating the number of turns required, if that ratio is correct.

It follows that the subsequent discussion about numbers of turns based on this unreferenced and probably invented ratio is also unreferenced and very likely original research (see WP:OR for more). An IP has already removed the discussion, but it was subsequently restored claiming that the maths is correct (which it probably is - I haven't checked it). However, it is based on the unreferenced claim.

Maxwell's paper makes great mention of the inability to position the parts with the required degree of accuracy and would certainly render the 0.5% improvement claimed (from 48 turns instead of 49) practically unobtainable - if, indeed, the improvement were theoretically possible - which has not be proven. It is also not clear if the galvanometer using the coils (which is what the paper is actually discussing) would benefit from such a small difference.

The ratios for the radius and positioning of the coils is not under dispute as these are stated by Maxwell in his paper. -RFenergy (talk) 14:35, 13 August 2020 (UTC)


 * I tried to find other sources for the ratio of the number of windings on the coils. I found a disjointed illustration which gave the ratio as $49/64$ but as it was not related to any text, I preferred to look for something better. I then found a site for a software simulator, and it too gives the ratio as $49/64$.
 * However, I did discover, that the article did quote the $49/64$ ratio before being altered to the (now apparently) incorrect ratio back in November of last year. Since this is referenced from Maxwell's work, I have restored this figure along with the similarly sourced additional point about removing variations up to the 6th order derivative. From the edit summary: the revised ratio claims to have been derived from a home attempt at constructing such a coil. This very definitely qualifies the change as original research which is forbidden.
 * Any other ratios or information should not be added to the article unless they are supported by a reliable and verifiable source that has more authority than Maxwell himself. 81.157.153.155 (talk) 13:29, 14 August 2020 (UTC)
 * Only Allah knows the true answer 65.24.123.196 (talk) 23:23, 17 June 2023 (UTC)