Net Inductance

Is this question about behavior of a spiral VIG?

I'd ask your instructor in class

Which has more turns, N or M?

Can you give the formula, with examples for each case?

"If one coil or the other were shorted", just lengthen it, until it's not shorted any more.

Homeworkhelp.com

"...just lengthen it..."

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Brilliant. Made my morning.

Are they identical but different because both coils follow the Fibonacci golden spiral a similar Fibonacci sequence but one truncates sooner than the other? What if the plane of one coil spiral is oriented orthogonal to another but the wavelength of the transmission frequency is N times larger than the distance between coils and M times smaller than the average radius of each coil.

Commendable work.

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I really like recent developments in the approach to handling the homework problem. A significant increase in clever and inspiring responses, often taking different approaches to solving the homework problem, seems to have taken firm hold in the responses to homework questions.

I was duly impressed as well. I wish I had that kind of command of the language.

I guess you need that in order to properly build a retro rotor encabulator.

OOOOooooouuummmmmmm......

You must be one with the beach......Antiparallelism should be avoided....

Just trying to shake the rust out of my electronics knowledge. It's been awhile. I would follow Fredski's advice and talk to my instructor, except that I haven't seen him in 34 years. All is not lost however as I found my answer on another website which offers great tutorials on the subject.

Thanks for your 'help' all the same.

Oh, I can't believe we let this happen again. Yet another one of those precious nameless posters has been lost to a nameless website offering tutorials.

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This is a tragedy. Who was scheduled for tutorial duty and who was scheduled for wayward drifting anonymous member watch?

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We need to get to the bottom of this. And by 'this' I mean the stack of anonymous posters who will not provide the minimum necessary information in their questions, yet display ferocious self-righteous indignation... which is kind of funny in itself since they are still in anonymous poster drag... when presented with CR4 rule conforming responses.

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I can think of no better place for self-righteous indignant anonymous posters that an unnamed eutopic website that has everything they want and desire.

Not a decepticon.

ROFL. What a setup fo the awesomeness that is your reply. Don't think I've seen a funnier coment than yours on here.

Why are you Anonymous? Is your question unimportant to you as well?

Just for the record, homework questions will not be answered.....

I personally like Redfred's answer the best. But I think he forgot you have to divide the magnectic flux by the ratio N/M times square root of 2pi*freq all divided by the diameter of the loop of the wire. It's inductance, so he obviously forgot the frequency part of the problem.

I didn't forget. I was just demonstrating most of the missing, pertinent information needed to properly attempt the problem, not to solve the problem. From the sparse amount of given information, a simple recipe solution would certainly be found to be inaccurate once measurements were attempted. The near and far field effects of antenna transmission and reception design starts with a sound understanding of Maxwell's equations, then things get complicated once a resonant cavity or a reflective surface (Earth, Ionosphere, Etc.) comes into the equations.

At the same time the question the OP made does imply some insight into the complexity of the problem. Instead of an inaccurate, simple answer I wanted to inspire the OP to look behind some of the correct doors of knowledge to grasp the stated problem.

Hopefully you didn't forget that inductance is a property of the coil's dimensions and anything nearby, frequency doesn't come into the equation until you want to know the the reactance or impedance of the coil at a particular frequency. From the ARRL Handbook for a small air coil:

L=(r² x N²)/(9l + 10d)

where:

• L = inductance (µH)
• r = outer radius of coil (in)
• l = length of coil (in)
• N = number of turns

Me? No I did not forget at all how to calculate the inductance of a single coil in free space. You seem to be forgetting that the OP is asking about two similar coils wired in series and parallel. Depending on the proximity and orientation of the coupling between these coils the impedance can be dramatically different.

Red, Sorry, my comment was directed at Melanie, the post that you responded to. I humbly acknowledge that you are the master of obfuscation, and would not want to encroach upon your territory.

Here are my thoughts on your problem.

In the real world, if you wanted to measure an inductance, you could apply an ac voltage across it and measure the current. Here's a thought experiment.

First consider what would result if M=N.

If the coils are paralleled, it makes no difference if the current goes through 1 wire or 2 wires. It still generates the same flux, so the inductance of both coils in parallel would be the same as the inductance of either coil by itself.

If the coils are anti-parallel, the current is divided equally and travels in both directions, resulting in zero flux, so the inductance would be zero.

If one coil is shorted, the other coil would appear to be shorted (or almost so) because the impedance is reflected through the transformer.

For the general case where M and N may or may not be equal, the above characteristics need to be met when N=M.

If M is greater than N, then you need to see how the situation differs from the case when M=N. The current is not divided equally. You can think of this as an equal current split plus a circulating current generated by the difference in number of turns M-N.

For the parallel case, this circulating current should make the M coil seem shorter and the N coil seem longer. I believe that this equivalent should be (M+N)/2.

For the anti-parallel case, I believe the equivalent should be (M-N)/2.

For the shorted case, you should still get zero (or close to it).

Inductance is proportional to the number of turns squared. You can think of it as "More turns create more flux, which in turn creates more induced emf in more turns (hence the square term)".

This was a really fun post!! I especially want to get one of those Retroencabulators into my next design!! Made my day!!