Wat is de belangrijkste energiedrager in de elektrische stroom die door een stroomkring loopt?
Ons wordt vaak geleerd dat het elektronen zijn. Zij bewegen zich door de stroomkring en brengen hun potentiële energie rechtstreeks over op het apparaat dat energie verbruikt. Maar deze uitleg is niet juist, althans niet helemaal.
Elektriciteit is de stroom van elektrische lading. Maar we vergeten vaak dat er een belangrijke component is, namelijk: de kracht die deze lading verplaatst.
Bedenk eens hoe de energie ons bereikt vanaf de elektriciteitscentrale, waar ze wordt opgewekt. Er is geen enkele kabel die onze huizen verbindt met de energieproducerende bedrijven. In feite zijn er veel gaten in het elektriciteitsnet, waar het circuit wordt onderbroken door een open ruimte. Dit gebeurt bijvoorbeeld in transformatoren. Elektronen kunnen niet door deze opening stromen, of toch wel?
Bekijk de volgende video waarin wordt uitgelegd welk fenomeen precies als energiedrager fungeert in elektrische circuits:
Commentaren
1) Derek is either intentionally or unintentionally being misleading. I will give him the benefit of the doubt and say it is the latter. He is implying that because the battery is about 1m away from the lightbulb, regardless of what the wires are doing, the fields will extend from the battery to the lightbulb at the speed of light and turn on the bulb. In actual fact, the positioning of the wires is very critical. In particular having the wires 1m apart creates a transmission line. Very crudely, you can think of this as an antenna or a capacitor. When you close the circuit, current is induced in the wires connected close to the bulb causing it to briefly light up similar to the behavior of a transformer. If the very far ends were disconnected as many commenters are wondering about, then the light would obviously not continue to be on. However, if it is indeed connected at the end, then the electric field would need approximately the speed of light around the wire to begin supplying the bulb with current. Derek is describing a single turn transformer, but trying to imply that the power magically travels from the battery over the air to the bulb regardless of what the wires are doing. Imagine if the bulb and battery were in the same locations, and the wires were the same length but laid out in a circle. i.e: like a figure 8, battery and bulb near the center, but wires are not closely coupled like ||, the explanation doesn't hold. After watching the video, would you feel deceived if I told you that the arrangement of the wires is critical? And only if they are 1m apart across the length that the bulb briefly turns on after 1/c (1lightsecond). And if the same length of wires were arranged in two giant loops, then it would not turn on after 1/c?
2) Are you suggesting that the scenario he lays out would basically be identical (for the lightbulb at the moment of t = 1meter/c), to two separate circuits (one for the lightbulb; one for the battery) of the same length/geometry as in the video, where each element (the battery and the bulb) are only connected to themselves? In other words, this:
__________________
|________L_________|
________B_________
|__________________|
Where B is the battery and L is the lightbulb, the distance between L and B is 1 meter, the distances between the front/back of each loop is also order 1 meter, and the total length of each loop is then order 10^8 meters.
At t=0, the battery (B) circuit is switched on. Then, just from inductance alone, the lightbulb (L) loop has a current induced, which partially lights up the lightbulb at t = 1 meter / c. Is that about right?
Because this is what I took from the video and this is largely uninteresting. It would mean that Derek completely obfuscated the reality of what was going on in order to make his example seem more amazing/special/impressive/confusing than it actually is...
3) Yup, you got it. The brief pulse of light at the start would be the same, but the difference would be that with what you've drawn the light will remain off, where as in Veritasium's setup after some amount of time the light will come on again. Basically the long lines act similar to a capacitor. In electronics, this effect is related to the concept of cross talk or interference, where you have one signal line close to another and it causes the other line to have some interference.
4) Gotcha, thanks!
Yeah, I tried to be clear about my example only being "the same" at exactly approx. t = 1/c, after which point the bulb from Derek's video would gradually brighten over the course of the next second and my hypothetical bulb on a separate circuit would not. More specifically, the hypothetical bulb on a separate circuit would achieve ~max brightness within an order of 1/c and then I assume it would gradually dim as conditions reached steady state and the change in flux with respect to time went to zero in the isolated bulb circuit. Although my memory of circuits/EM is a bit faded and unsophisticated at this point.
Thanks also for the link. I remember visiting that site for various things when I was designing PCBs for an atomic physics lab I worked in during undergrad (I since left experiment to do computational physics and I am much happier!).
5) Am I correct in thinking the same thing would happen if the two lines weren't connected to anything at all? Like if I just laid out two parallel light-seconds of wire but didn't connect them to anything and turned the battery on.
-----------B-------------
-----------L------------
Cause the battery can't "know" whether or not it's connected to a circuit a light-second down the line right? Is it just acting like a capacitor?
6) Yup, exactly the same at the start. If we want to nitpick, your scenario is actually closer to veritasiums than the two loops, since that has 4 wires in parallel.
7) No... current flow is required to get electric and magnetic waves. Without completing the circuit on the battery you have no current flow and no waves to propogate to the light wire.
8) The battery can't know whether or not it's in a loop or not until a second has passed, or else you'd violate light speed. Something has to be flowing before then.
And current can flow (briefly) in circuits that aren't fully connected by wires, for example see a circuit with a charged flat plate capacitor which has an air gap. The people above are saying that the wires are acting as transformers/antennae.
9) So, the cable does get energized when it touches the cable right, or am I misrepresenting it...?
10) More comments...
Anders gezegd: het laatste is daarover nog niet gezegd, maar toont wel aan dat er nog heel wat mysteries zijn. 
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