Electronics > Beginners
Magnetic Permeability
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ivaylo:
The best 50 min you can spend on the subject - https://youtu.be/4UFKl9fULkA
T3sl4co1l:

--- Quote from: bob91343 on June 22, 2019, 04:07:31 am ---I remember asking a college instructor why the curve of inductance has that first tiny bend in it, very close to the origin.  I never could get an answer but now I know.  What this has taught me is that, just because someone teaches a subject or writes a book on it doesn't mean he understands the subject.

--- End quote ---

Although this isn't their fault; condensed-matter physics is notoriously hard (in fact, provably without general solution*), and ferromagnets are very hard indeed to solve.  Like superconductivity, this is one of many outstanding problems in physics to this day.

*This goes something like, we can make a Turing machine with condensed matter, therefore at some level, condensed matter necessarily leads to the Halting Problem, and is therefore provably unprovable.

Tim
pwlps:

--- Quote from: T3sl4co1l on June 22, 2019, 06:21:33 am ---*This goes something like, we can make a Turing machine with condensed matter, therefore at some level, condensed matter necessarily leads to the Halting Problem, and is therefore provably unprovable.

--- End quote ---

Wow, this is an interesting philosphical point of view  :). But I think it doesn't makes sense.  First you can't tell the quantum physics of condensed matter is provable or unprovable because it is not a purely logical construction.  Second the physics of the Turing machine is not at the same level as it's logic: the halting problem is just a version of the Godel theorem applied to the logic system of programming but it can't tell anything about the theory of the logic gates that are used in the machine: the theory behind the gates does not belong to the logic system that exhibits the halting problem.
Sorry for this off-topic post, it was just to challenge Tim's philophical thoughts  :)
bob91343:
When someone does scientific work, it's subject to peer review.  He publishes it and others review, comment, and challenge in an attempt to arrive at the truth of the matter.

When someone is hired as an instructor, or writes a book on a scientific subject, that doesn't happen.  The qualifications are noted (sometimes all too casually) and a decision made based on the usual criterion, money.

I see technical articles all the time with gross errors.  Publishers save money on proofreading.  Some articles are so bad that they are nearly incomprehensible.  Is this a relatively new syndrome, or has it always been thus?

Sorry if this is off topic but I had to vent.
ramonest:
Thank you all for answering.
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