Talk:Inductance

Loop of wire

I have reverted this edit which has the edit summary changed "wire loop" to coil of wire. The quoted formula contains N respresenting a number of turns of wire. For a wire loop N is 1 and would not be included in the formula. I agree that the use of loop here is problematic and could , perhaps, be improved, but coil of wire is even more so. I think the definition only works if all the turns are essentially co-incident - that is, lying on the same loop. Furthermore, the change was not done consistently, the section continues to talk about wire loop further down. SpinningSpark 16:29, 9 August 2010 (UTC)

The equation for the inductance of a thin solenoid is not correct; one should use Babic and Akyel, Improvement in calculation of the self- and mutual inductance of thin-wall solenoids, eq. (8), IEEE Trans on Magnetics, Vol. 36, No. 4. July 2000 Prof. J.C. Compter —Preceding unsigned comment added by 194.25.102.189 (talk) 10:04, 2 September 2010 (UTC)

The Lorenz expression for the inductance of a coil is the inductance of a cylinder with a current around its surface (might be indicated in a footnote), and as such is as exact as Maxwell's equations. Improvements (wire or coil thickness, wire spacing) are more complicated and less instructive. B&A use numerical methods. Appears that FEM and numerical methods should be mentioned (with references) under calculation techniques. —Preceding unsigned comment added by Rdengler (talk • contribs) 08:21, 4 September 2010 (UTC)

confusing wording

In the opening paragraph, I find the following sentence to be confusing: "This is a linear relation between voltage and current akin to Ohm's law, but with an extra time derivate." In fact, the voltage across an inductor is not proportional to the current -- it is 90º out of phase with it if the reactance is perfectly inductive.Jdlawlis (talk) 01:43, 18 December 2010 (UTC)

I agree. The statement is technically correct and mentions an important point, but should not be in the introduction. --Chetvorno^TALK 04:27, 18 December 2010 (UTC)

-Shouldn't be confusing, taking the time derivative is a linear operation, the statement is mathematically correct. radical_in_all_things (talk) 08:30, 19 December 2010 (UTC)

Most people reading the introduction will be nontechnical people looking for the simplest possible explanation. The defining equation belongs there, but discussion of its linearity does not. The connection of inductance with magnetism isn't even mentioned until the 4th para. This is why people complain wikipedia articles are too technical. --Chetvorno^TALK 20:16, 19 December 2010 (UTC)

The statement is not mathematically correct. It would be correct if it were written: "This is a linear relationship between voltage and the rate of change of current akin to Ohm's law, except that current is replaced by its derivative." The fact that the derivative is a linear operation does not relate to this particular issue. As an example, take an ideal RL circuit with an AC generator. Let V(t) = V₀cos(ωt) be the voltage generated by the AC generator. It follows that the current $I(t)=\frac{V_0}{Z}cos(\omega t-\delta)$, where the impedance $Z = \sqrt{R^2+(\omega L)^2}$ and the phase constant $\delta = tan^{-1}(\frac{\omega L}{R})$. The voltage drop across the inductor, $V_L=\frac{\omega LV_0}{Z}sin(\omega t-\delta)$. If the voltage across the inductor were indeed proportional to the current, you would be able to multiply the current times a constant to achieve the voltage. Multiplying a cosine function times a constant will only change its amplitude -- it cannot transform it into a sine function. Hence the voltage across the inductor is not proportional to the current through the circuit. These equations can be found in any introductory E&M textbook such as Tipler or Purcell. Jdlawlis (talk) 23:36, 20 April 2011 (UTC)

It is mathematically correct to state that inductors are governed by a linear equation. It is not correct to state that there is a linear relation between voltage and current, and it is even more incorrect to state that the governing equation is analogous to Ohm's law. The Ohm's law analogy only applies to the r.m.s. values of sinusoidal voltages and currents and requires the introduction of the concept of reactance to replace resistance in Ohm's law. SpinningSpark 06:13, 21 April 2011 (UTC)

I agree with everything you say, SpinningSpark. I think it would be clearer if the Ohm's law reference were removed. Jdlawlis (talk) 14:11, 21 April 2011 (UTC)

What really gets mixed up here is proportionality (linear equation) and linear relation. The statement is correct in that the voltage generated by the sum of two (time dependent) currents is the sum of the voltages generated by the individual currents (as it is in Ohm's law). This would be a practically useful information, but if it is confusing, it need not be in the introduction. radical_in_all_things (talk) 06:49, 22 April 2011 (UTC)

I would suggest a compromise solution here. You can begin with a simple explanation stating, "We can view this in similar terms to Ohms Law, except that unlike Ohm's law..."

Well you can see what I am saying. Mostly, this article should be written so that any layman, or high school student can understand.

Your thoughts?Sunshine Warrior04 (talk) 07:44, 26 October 2011 (UTC)

Original research or lack of references

The section on "coupled inductors" has a paragraph at the bottom about tuned circuits, starting "When either side of the transformer is a tuned circuit, the amount...". This paragraph is not referenced and may be original research. Does anyone know where this material comes from? —Preceding unsigned comment added by 121.98.140.35 (talk) 00:01, 20 May 2011 (UTC)

I don't know where the material comes from but this is a well-known effect much used in the design of RF amplifiers and covered in numerous textbooks (eg [1][2][3]). Whether it beklongs in an article on inductance is another question. SpinningSpark 09:29, 24 June 2011 (UTC)

Self-induction

The entire section on calculating self-induction needs to be re-written. It is neglecting explainations of internal and external inductances, and not properly explaining the Neumann formula. Also it doesn't mention the method of partial inductances (Rose, Grover, Ruehli). — Preceding unsigned comment added by 129.139.1.68 (talk) 14:37, 21 June 2011 (UTC)

The changes done under 'self inductance' are misleading in several ways, I undid these changes. 1) The text now repeatedly mentions filaments, while self inductions isn't defined for filaments. 2) To say R >= a/2 is outside the filament makes no sense. 3) The distinction between external and internal inductance makes no sense. The total inductance simply is the sum of the product of current elements i(x)i(x')d³xd³x' divided by distance R(x, x') (see Self inductance. It really is as simple.) The expression for M_i,i consists of two contributions only for technical reasons, and the choice R >= a/2 is a matter of convenience. Partial inductancies are a different thing. Hic est Rhodos. radical_in_all_things (talk) 07:38, 24 June 2011 (UTC)

The formula for inductance in coaxial cables is only missing the constant mu-nought = 4*pi*10^-7 (as a coefficient at the beginning) (cite: Giancoli Physics for scientists and Engineers vol.2, 4th edition) — Preceding unsigned comment added by 152.7.59.119 (talk) 01:54, 18 October 2011 (UTC)

No, the constant mu-nought isn't missing, it is in the column caption describing the columns content.radical_in_all_things (talk) 14:56, 19 October 2011 (UTC)

A reference for the self-inductance curve integral is [4]. It will be added to the article when on arXiv.org.radical_in_all_things (talk) 13:18, 3 December 2011 (UTC)

Nomenclature

In the section on non-linear inductance the Greek symbols are not defined. Even i and t are not obvious to all readers (instantaneous current and time) but Φm is not, and doesn't seem to be defined explicitly anywhere in the article. Please remember that people often read these articles because they want things EXPLAINED, they do not want to be frustrated by unexplained symbols. — Preceding unsigned comment added by 210.48.109.11 (talk) 06:44, 9 August 2011 (UTC)