zippy
pfm Member
In fact everything I've learned about everything turns out to be untrue. Why do we bother to learn anything ?
Electricity Doesn't Flow Through Wire
- Thread starter Mike Hanson
- Start date
ks.234
Half way to Infinity
Because otherwise we might vote Tory!Why do we bother to learn anything ?
Nick_G
pfm Member
Is that Herbie Hancock on that second video? Might be worth watching that.
Mullardman
Moderately extreme...
Yebbut....
If the energy flows in the surrounding fields, but not in the wires, answer me this.. How is it that I could sit safely between the bulb and the battery, next to the switch, and be unharmed by an e.g. 230v 'circuit'...yet..if I touch the conductor in which the electrons are not moving..I will get a 'belt'? (William Hartnell Dr Who voice.. Mmmm? Mmmm?)
If the energy flows in the surrounding fields, but not in the wires, answer me this.. How is it that I could sit safely between the bulb and the battery, next to the switch, and be unharmed by an e.g. 230v 'circuit'...yet..if I touch the conductor in which the electrons are not moving..I will get a 'belt'? (William Hartnell Dr Who voice.. Mmmm? Mmmm?)
Sue Pertwee-Tyr
Accuphase all the way down
Also, why does the gauge of the conductor matter? Apologies if this is covered in the OP video, which I didn’t watch all the way through.
TheDecameron
Unicorns fart glitter.
God, the Great Creator can not be understood by even the greatest minds let alone yours. Black Holes as you know them are access ports through which he reaches to move things from time to time to see if anyone notices.
Joe Hutch
Mate of the bloke
This is exactly why I chose to study English.
Nick_G
pfm Member
I've often wondered whether new universes are born every time a star collapses into a black hole.
Jim Audiomisc
pfm Member
I was initially asked by a puzzled Prof of Theoretical Physics. His field (pun alert) wasn't electrical.
The answer/explanation makes sense via understanding Transmission Lines. That also explains why the wire gauge and spacing matter, etc.
The cable only 'guides' the connection. Information takes time to get from one end to the other, but in a context where that time is 'short' the response seems to humans 'instant'. But it isn't. Transmission Line Theory lets you work out the details.
The answer/explanation makes sense via understanding Transmission Lines. That also explains why the wire gauge and spacing matter, etc.
The cable only 'guides' the connection. Information takes time to get from one end to the other, but in a context where that time is 'short' the response seems to humans 'instant'. But it isn't. Transmission Line Theory lets you work out the details.
Mullardman
Moderately extreme...
John Phillips
pfm Member
I think that's potentially what I describe as a "dishonest question" (with no intent to offend - I address my comment to the question).
What is observed does not, I think, need an "instant" response from the power generator at all. And I do note the quotes so I think the question is actually being honest if someone pays attention.
Without the hint from the quotes, he question contains the seeds of an inappropriate answer. I think instantly the generator knows nothing and the current you get is "stolen" from places that are much more local until the generator eventually notices and responds.
I have spent some professional time as a governing board member for an industry association and learned there that you have to be very careful that the questions you choose to address are "honest", if you are not to risk doing the wrong thing based on getting prejudiced answers.
Jim Audiomisc
pfm Member
Long-term users of PFM may recall earlier discussions about some old HFN articles by Hawksford which presented misleading results and conclusions. Again, an example of not knowing the relevant EM theory.
If you run a current though a pair of wires that are resistive you get a change in voltage *along* each wire's surface because it is needed to make the current flow though the wire's resistance. EM theory uses the Poynting Vector to indicate power flow. This is perpendicular to the E field and the H field. Thus this 'resistive loss' power points *into* the wire, heating it up. Inside the metal of the wire the EM field is radial (assuming wire with a round cross section). it only appears again externally as heat. It isn't freely propagating, but shoving the electrons about a tiddly bit, and dies as soon as you remove the driving field so far as the external world can tell. (For the mathematicians, the internal field is a 1st order differential one, not the usual free space 2nd order that causes EM waves to propagate in free space.)
The problem is that most people - even learned profs - often fail to twig these things because it isn't, erm, their field.
Fortunately, with the exception of some who want to flog hyper-costly cables, none of it really matters except for those who like to know how things work.
If you run a current though a pair of wires that are resistive you get a change in voltage *along* each wire's surface because it is needed to make the current flow though the wire's resistance. EM theory uses the Poynting Vector to indicate power flow. This is perpendicular to the E field and the H field. Thus this 'resistive loss' power points *into* the wire, heating it up. Inside the metal of the wire the EM field is radial (assuming wire with a round cross section). it only appears again externally as heat. It isn't freely propagating, but shoving the electrons about a tiddly bit, and dies as soon as you remove the driving field so far as the external world can tell. (For the mathematicians, the internal field is a 1st order differential one, not the usual free space 2nd order that causes EM waves to propagate in free space.)
The problem is that most people - even learned profs - often fail to twig these things because it isn't, erm, their field.
Fortunately, with the exception of some who want to flog hyper-costly cables, none of it really matters except for those who like to know how things work.
Marchbanks
Hat and Beard member
Is it because Alexa watches us all the time and passes the information on?
Jim Audiomisc
pfm Member
That's the point. In the context of a Physics undergrad course they need to spot that 'instant' is a dodgy term that misleads. Hence the indication as I can't speak via PFM or raise an eyebrow.
Spotting this then directs them to an answer they probably hadn't realised before.In effect, the power grid is a mess of mismatched transmission lines trying to feed an ever-changing set of - usually mismatched - loads to a set of varying generators. Amazing it works at all given that electrons probably can't solve Maxwell's Equations, even when given a piece of chalk.
However the good news is that many learned Profs also get puzzled by it when it occurs to them.
Jim Audiomisc
pfm Member
Has she done EE101?
Marchbanks
Hat and Beard member
She hasn’t managed to worm her way into Marchbanks Towers, so unfortunately I can’t ask her. Please don’t tell anyone I operate an Alexa-free zone - Jeff has already built a giant operations centre just a few miles away, I think he can sense an infidel nearby. I did ask the lady that lives in my phone if she had taken EE101, though. She came back with a link to Robocop, so I think it’s safe to say she is being suspiciously evasive.