Magnet Myths and Misconceptions

[Pirate88179]

True enough... but....

http://en.wikipedia.org/wiki/Electromigration

"Electromigration reliability of a wire (Black's equation) Main article: Black's equation At the end of the 1960s J. R. Black developed an empirical model to estimate the MTTF (mean time to failure) of a wire, taking electromigration into consideration. Since then, the formula has gained popularity in the semiconductor industry. :^[3][5]

"The temperature of the conductor appears in the exponent, i.e. it strongly affects the MTTF of the interconnect. For an interconnect to remain reliable as the temperature rises, the maximum tolerable current density of the conductor must necessarily decrease. However, as interconnect technology advances at the nanometer scale, the validity of Black's equation becomes increasingly questionable."


TK:


This is exactly what I was talking about in theory except, it does not appear to be a large problem until you get down to a very small scale.  Although, it appears that Black developed this equation to determine the reliability of a wire over time so that seems to indicate that some changes are taking place inside the conductor.

Possibly MH's post about the impurities in the copper (or other conductor) affecting its properties over time is the basis for this maybe?  As he posted, when these micro cracks appear this would raise the resistance of the conductor and therefore possibly cause some heating which might further degrade the conductivity of the wire, etc. (Domino effect)  Very interesting stuff here.

I know I am going a little far afield of the topic but,  I really want to know exactly (if possible) what is happening inside a conductor when electrons vibrate within it or move through it.  After all, it is this activity that creates our magnetic field around these conductors right?

Sorry that I credited MH with the Newton's ball example that you posted.  (Thanks MH for pointing that out)

This is a great topic here fellows.

Bill

[minnie]

Is there such a thing as "skin effect" where there is more conduction on
the surface of a conductor? Multi-strand wire ought to have good performance.

[Pirate88179]

Is there such a thing as "skin effect" where there is more conduction on
the surface of a conductor? Multi-strand wire ought to have good performance.

I believe that multi-strand wire has less resistance than a solid wire of the same diameter.  (I think)  Does this mean that the strands are insulated individually themselves from each other like magnet wire?  Or, is it just a bunch of small, bare wires (all shorted together) having more additive surface area?  I guess I am being lazy here as I could just look this up.

Bill

ETA  I just read that due to the skin effect, multi-strand wire will have less resistance as most of the current flows along the surface of the individual wires.  I have no idea if this is true or not but googled it and read this in several places.

[bboj]

Seriously? It is a fundamental property of matter, one of the "quantum numbers" that describes certain kinds of subatomic particles. It is a conserved quantity, just like momentum or energy. It is that property of matter that causes the associated particle to move in certain ways under certain conditions. It comes in two "polarities" that we arbitrarily call positive and negative. Charge is quantized, which means it comes in discrete amounts, the smallest of which is the Unit charge, and the electron is the particle which carries the Unit Negative Charge.

What is "wetness"?

I got that more or less. But than as Point. asked - Why is magnetic field around a conductor with a dc current static?

[TinselKoala]

I got that more or less. But than as Point. asked - Why is magnetic field around a conductor with a dc current static?

An unchanging DC current, perhaps you mean? I can take my DC current of one amp, increase it to two amps, and while I am increasing the current, the magnetic field also increases.
You have got to get past these "why" questions, though. Why is there air? To fill up basketballs with, of course.

Charge, motion and field are related by a rigorously defined set of relationships that are mathematically precise. These relationships are contained in Maxwell's Equations, the Biot-Savart force law, and the Lorentz force law. Why do these relationships exist? So that there will be air to fill up basketballs with, of course.

Here, knock yourself out. (MH, you  might also be interested in taking a look at this document. Warning: math ahead.)

http://www.physics.uwo.ca/~mgc/EM1sec5.pdf