The Big Misconception About Electricity

sunshine_eggo

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I thought that for the longest time. I'm posting this before I watch it even though it's still on the honor system since you can't tell when I watched it.

IIRC, the energy is propagated by the induced magnetic field. The electrons move far slower than I ever thought.

Off to the vid...
 

sunshine_eggo

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Sweet.

Clearly I watered it down so I could remember the concept but not the details. Very cool explanation.

I didn't get the right answer. :)
 

svetz

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I believe that's what Tesla was trying to accomplish with wireless power (e.g., if all it takes for energy to flow is an electrical field in sync with a magnetic field, then you could couple Earth's existing magnetic field with an electrical field to distribute power wirelessly worldwide).
 

RayfromTX

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I got the answer right by intuition but not by understanding the concept beforehand. Story of my life but I'll take it. Thanks for posting.
 

Cal

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Seems like the guy is mixing apples with oranges. I don't believe there's any difference in DC power in a shielded or non-shielded cable. The electric field will be shorted to the shield, but has no effect on power transmission.

DC power is still defined by voltage times current, or current squared times resistance. DC resistance has no inductance or capacitance component.
 

svetz

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I got the answer right by intuition but not by understanding the concept beforehand. Story of my life but I'll take it. Thanks for posting.
I didn't get it right, I knew about the fields but assumed they propagated at c. That they're FTL was interesting.
 

FilterGuy

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That they're FTL was interesting.
The key is in the fact that the battery and light are right next to each other.... not that the wires are so long.
Consequently, the energy is not traveling FTL. But I have to admit that I don't really understand the physics of it.
 

hhtat

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Not a big fan of this video. While it's technically correct, it's extremely misleading. The power induced through the bulb when the switch closes is due to RF. It would be induced even if the bulb was disconnected from the circuit at the far ends of the wire loop.

If the entire circuit was shielded including the battery, switch and bulb, it would take 1s to notice anything at the bulb.

They basically leave viewers questioning their understanding of electricity due to a minor technicality.
 
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upnorthandpersonal

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Funny, I talked about that way back when:

 

Supervstech

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Not a big fan of this video. While it's technically correct, it's extremely misleading. The power induced through the bulb when the switch closes is due to RF. It would be induced even if the bulb was disconnected from the circuit at the far ends of the wire loop.

If the entire circuit was shielded including the battery, switch and bulb, it would take 1s to notice anything at the bulb.

They basically leave viewers questioning their understanding of electricity due to a minor technicality.
What do you mean?

If the wires were disconnected?

Minor technicality?
 

circus

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Wouldn't be the first time humans exploit "it" without understanding what "it" is. Until then, clumsy nonsensical models is the norm.
Makes you wonder what other phenomena is out there that we're oblivious to.
 

svetz

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The key is in the fact that the battery and light are right next to each other.... not that the wires are so long.
Consequently, the energy is not traveling FTL. But I have to admit that I don't really understand the physics of it.
I did confirm that the field propagation is limited by c. Seems like it should take a second for the field to propagate that distance and it should follow the wire. I wouldn't think the EM force could reach the bulb a meter away with enough force to do anything.

What he says is:
I think a lot of people imagine the electrical field needs to travel from the battery, all the way down the wire which is a light-second long so it should take a second for the bulb to light up. But what we've learned in this video is it's not really what's happening in the wires, it's what happens around the wires and the electric and magnetic fields can propagate out through space to this light bulb which is only 1 meter away in a few nanoseconds. So, that is the limiting factor for the lightbulb turning on.

Now, the bulb won't receive the entire voltage of the battery immediately. It'll be some fraction which depends on the impedance of these lines and the impedance of the bulb.

I wouldn't want to bet against him. But, perhaps there will be a correction or update? ;)
 

Posplayr

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I believe that's what Tesla was trying to accomplish with wireless power (e.g., if all it takes for energy to flow is an electrical field in sync with a magnetic field, then you could couple Earth's existing magnetic field with an electrical field to distribute power wirelessly worldwide).

That would perfectly explain why they never taught the concepts this way in my EE undergraduate program. I vaguely remember the Poynting vector but it was probably in E&M II and although there was an association between Maxwell's equations and a generalization of Ohms law these concepts were never explained as in the video.
 

hhtat

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What do you mean?

If the wires were disconnected?

Minor technicality?
If you add two more switches to the circuit at opposite ends where the wire bends - and open those two switches half a second before you flip the main switch - you'll still see some RF (+ maybe capacitance?) induced voltage at the bulb even thought the circuit is incomplete.

Again, I find this video extremely misleading. It's correct on a technically but it doesn't state it that way. Instead it states it in the way that "electrical energy doesn't flow through wires."
 

Posplayr

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I'm having to reach back a long way into my E&M I& II classes and I'm not even sure I can find the textbook but I'm finding this video fascinating the further I dig into it.

Even if we simply view it as a 3D visualization of a complete set of fields and E and the M field circuits for the simple light buld circuit, I think the only way to interpret it is that there are necessary conditions (i.e. if-and-only if(iff)) for the current to flow (as per ohms law) and have the associated E and M as per Maxwell and Poynting.

Another way to say this is that the current does not cause the magnetic field any more than the magnetic field causes the current flow. They are inseparable and you can't have one without the other (i.e.e iff).
 
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