Understanding Electricity Flow in a Conductive T-Shape Structure

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In summary, the conversation discusses a T-shaped metal structure that is struck by lightning at one end and how the current flows through it. It is explained that the electric field pushes the electrons, resulting in a current, and that there is a finite probability of discharge. The questions raised involve how the electricity "knows" which direction to flow and how it makes the "choice" between two identical paths. The expert summarizer explains that the current flows towards the ground due to the path of least resistance, similar to how water would flow in the same situation. The concept of electrons being intelligent is dismissed.
  • #1
KingOrdo
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Imagine the following conductive structure built outside:

A
||
||
B|_____C
||
||
----------------------

Basically, a T-shaped piece of metal, with one end stuck in the ground, one end pointed into the air (A), and one end horizontal, parallel to the ground (C).

Let's say lightning strikes the structure at point A. Current flows down until it arrives at point B. Here it has to make a 'choice', and my understanding is that all of the current proceeds to the ground. I.e. a measurement at point C will never show any electric current there (assume we're in a vacuum so the ambient 'air' is not conductive).

How does the electricity 'know'--without ever investigating the horizontal element--the way to ground? When the first element of current arrives at point B, why does it automatically proceed to ground? How does it 'know' this is the 'right' way to go?

Thanks in advance.
 
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  • #2
The electric field will also push electrons in part C of your structure, resulting in a pile up off charge (measurable as a voltage). Charge being pushed in part C just can't go anywhere. Moreover, don't think of the current as just a fast train of electrons: the electrons might not be moving fast at all, but the field pushes ALL electrons almost instantaneously, resulting in the current. There's also a finite probability that the electrons WILL go from part C to the ground (static discharge). It's just highly unlikely.

Edit: Let me clarify my usage of 'electric field' here: when the first electron starts to move this would cause a nonzero electric field which has to be compensated, resulting in the aforementioned current.

I hope I got this all right.
 
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  • #3
Let's start with the lightning first. Why does a lightning strike the conductor in the first place? Because there exists a height dependent electric potential. Since the potential depends only on height, points B and C would have the same potential and so no charge would flow between them.
 
  • #4
Let's forget the issue of lightning totally: at the top of the structure (A) we have a car battery that, when a switch is thrown, discharges electricity into the structure.

Here are the questions:
(1) Will a measurement of current at (C) be zero? Remember that this contraption is in a vacuum so there is no conductivity between (C) and the ground.
(2) Regardless of how we want to parse it, when the switch is thrown, current will begin to flow from the battery towards the ground. When current reaches (B), how does it "know" to proceed to the ground, and not to point (C)? Is it not the case that locally there is no difference between the little piece of metal heading to ground and the little piece of metal heading to (C)?
 
  • #5
KingOrdo,
1) Yes, nil current at C.
2) Imagine a flood of electrons from A. When they reach the junction B they do begin to pour in both directions but the ones that go towards C quickly start to just pile up, since they can't get any further, whereas the rest (those going towards the bottom) freely flow out into the ground. Compared to the bottom of the T, this leaves the C arm more negatively charged (repelling any further electrons), so the vast majority of the current from A must now flow directly to the ground.
 
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  • #6
cesiumfrog said:
KingOrdo,
1) Yes, nil current at C.
2) Imagine a flood of electrons from A. When they reach the junction B they do begin to pour in both directions but the ones that go towards C quickly start to just pile up, since they can't get any further, whereas the rest (those going towards the bottom) freely flow out into the ground. Compared to the bottom of the T, this leaves the C arm more negatively charged (repelling any further electrons), so the vast majority of the current from A must now flow directly to the ground.
Thanks. A couple follow-ons, if you don't mind:
(1) How does that first electron to reach the vertex B 'choose' which way to go? The two paths are identical to the electron; what is the mechanism that determines which path is traveled?

(2)After the charge has "pile[d] up" in the arm, how do the electrons arriving at B 'detect' that and make the 'choice' to go to ground?
 
  • #7
You are using words that imply that electrons are intelligent and you simply need to drop that concept to understand what is going on. This concept is exactly the same as how water would flow in an analagous situation. "The path of least resistance" simply means water or electricity flows where there is less obstruction. How does water "know" not to flow through a dam? It doesn't - it just hits the dam and stops.
 
  • #8
russ_watters said:
You are using words that imply that electrons are intelligent and you simply need to drop that concept to understand what is going on. This concept is exactly the same as how water would flow in an analagous situation. "The path of least resistance" simply means water or electricity flows where there is less obstruction. How does water "know" not to flow through a dam? It doesn't - it just hits the dam and stops.
Yes, but in my situation (1) there is no "obstruction"--both paths are locally utterly identical to the electron. Yet my understanding is that it will "choose" the one to ground each and every time.

And in (2), the same argument exists until the charge has "pile[d] up" in C to such a degree that electrons physically prevent movement into the arm. otherwise, it's action at a distance which doesn't make any sense to me. . . .
 
  • #9
KingOrdo said:
Yes, but in my situation (1) there is no "obstruction"--both paths are locally utterly identical to the electron. Yet my understanding is that it will "choose" the one to ground each and every time.
Not so, the path, B - C - Ground has a larger resistance than that of B - Ground.
 
  • #10
KingOrdo said:
Yes, but in my situation (1) there is no "obstruction"--both paths are locally utterly identical to the electron. Yet my understanding is that it will "choose" the one to ground each and every time.
No. As already said, the instant the power is turned on, some electrons will flow into the non-grounded part. But they will quickly start to "pile up" and physically/electrically obstruct the path of other electrons.

Imagine water flowing through a trough with a Y in it. On one side of the Y, the trough keeps going, on the other side, it is blocked after a little bit. If you start pouring water into the trough, it will flow both into the open and obstructed sections until it fills up the obstructed section and only flows through the open section.

For your piece of metal, btw, the obstruction is the air around it.
And in (2), the same argument exists until the charge has "pile[d] up" in C to such a degree that electrons physically prevent movement into the arm. otherwise, it's action at a distance which doesn't make any sense to me. . . .
The way you worded it is a little confusing. I'll reframe what happens:

When you first connect the battery, there will be an initial inrush of current into the entire object (part 1 of what happens). But remember, the object is already pretty much filled with electrons, so if you could take a photo of the object before and after you flipped the switch, they'd be pretty much indistinguishable. The inrush also takes only a tiny fraction of a second. And btw, since "c" is the end of the object, there will be no current measured there even during inrush.

After reaching equilibrium (part 2 of what happens), electrons are physically obstructed from moving through the unconnected section of the object, and thus only move through the grounded section.

This really is relatively straightforward and wizzart answered it quite adequately in the first reply. I'm not sure what it is you are misunderstanding.
 
  • #11
why dose lightning go towards the ground? how dose it "know" that that is the way to go to get to the ground? why dose it not just go which ever way has less resistance? assuming all ways around it is air why dosent it go sideways or up if the resistance there is just marginally less than down
 
  • #12
Lightning does not always go towards the ground, it goes in the direction where there is the least resistance and most voltage. Sometimes that is a meandering path toward the ground and sometimes that is toward a cloud.
 
  • #13
Sometimes it does go up also - http://www.physorg.com/news10961.html" [Broken].

This will give you a good idea of what lightning is doing during a strike. Note the multiple attempted paths that it takes at the beginning. It's trying to find the path of least resistance - http://www.youtube.com/watch?v=2XwFF5idD_0".
 
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1. What is electricity and how does it work?

Electricity is a form of energy that is created by the movement of electrons. It is produced by various sources such as power plants, batteries, and solar panels. The movement of electrons from one atom to another creates an electric current, which can power devices and machines.

2. What are the different types of electricity?

There are two main types of electricity: AC (alternating current) and DC (direct current). AC electricity is the most commonly used type and is what powers our homes and appliances. DC electricity is mainly used in batteries and smaller electronic devices.

3. How is electricity measured?

Electricity is measured in units of power called watts (W) or kilowatts (kW). The amount of electricity used over a period of time is measured in kilowatt-hours (kWh). This is the standard unit used by utility companies to calculate your electricity bill.

4. What are conductors and insulators?

Conductors are materials that allow electricity to flow through them easily, such as metals. Insulators, on the other hand, are materials that do not allow electricity to pass through them easily, such as rubber or plastic. This is why electrical wires are wrapped in insulating material to prevent accidents.

5. What are the safety precautions for dealing with electricity?

When working with electricity, it is important to follow safety precautions to prevent accidents and injuries. This includes wearing protective gear, turning off power sources before working on electrical equipment, and avoiding contact with water when using electrical devices. It is also important to hire a licensed electrician for any major electrical work.

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