# Can current flow in both directiosn simultaneously?

Discussion in 'General Electronics Chat' started by geratheg, Aug 19, 2014.

1. ### geratheg Thread Starter Member

Jul 11, 2014
107
3
Can current flow in opposite directions simultaneously through the same wire?

Attached is a schematic. The two voltages are unknown and could be different values. Both are after some circuit above them, also unknown. The circuits are separate from each other above the point of voltages.

Assume the entire circuit uses the same power source.

Up until now, I thought the connection of those two schematics is exactly the same thing, just different points.

1. But then I questioned the behavior of current, and wonder if it would sometimes be better to wire it one way over the other because of this. Is this ever a consideration? Or are those setups exactly the same and current adjusts behavior such that it would work?

2. For example, lets say currents from both of those voltages both share load 1 and load 2. This makes sense in setup 2.
In setup 1 only one load appears to be able to be shared, either load 1 or load 2, unless current is able to flow in two directions in the same wire simultaneously. For example, assume load 1 is shared, load 2 would have to get its current from the left "+" because current from the right "+" is blocked from going to the left due to opposite directions of current as shown by the arrow with a question mark in the attached picture.
Is this possible?

I hope my explanations make sense.

Also, spelling error in title. I hope a mod can fix it

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2. ### crutschow Expert

Mar 14, 2008
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Not sure I completely understand you examples but the answer to your question is no. Current can only flow in one direction. It's just a question of which node has the higher voltage. The current will always go from the higher potential to the lower. Consider the current as water flowing in a pipe. Flows in one direction only as determined by the relative pressures.

3. ### alfacliff Well-Known Member

Dec 13, 2013
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curreent can flow both ways in rf circuits. both the foreward wave and the back wave (swr). most other current is only one way.

4. ### ErnieM AAC Fanatic!

Apr 24, 2011
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I cannot tell what your circuit is doing, so I drew another one I can tell what is happening:

We have two batteries connected to two resistors. The currents of 1A and 2A should be obvious. What is interesting is the current thru wire A-B.

With just B1 there is 1A from B to A. With just B2 there is 2A from A to B.

The net current is the sum of 1A from A to B.

Now let's make a slight change:

With this simple change we make a real current of 1A from B to A, and a real current of 2A from A' to B'.

Note there is no current from A to A'.

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• ###### I-2.bmp
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5. ### MikeML AAC Fanatic!

Oct 2, 2009
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Ernie, isn't the current in the lower branch of the upper diagram supposed to be 1A?

The principle that Ernie is describing is called Superposition

6. ### ErnieM AAC Fanatic!

Apr 24, 2011
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Yep, perhaps I could have been more clear when I said:

7. ### wayneh Expert

Sep 9, 2010
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I'm not buying that. The sum of all waves at any one point in a real conductor results in a potential at that point, at that instant. Current will only flow from higher to lower potential, and that point in the conductor cannot be simultaneously higher and lower in potential than its neighbor.

It may be a useful analytical method to consider a backwards wave.

Oct 2, 2009
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9. ### BR-549 Well-Known Member

Sep 22, 2013
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No. In some experiments, the skin effect might confuse some, but no. It's one direction at one time. Ernie's first picture is not representative of current flow in the circuit. None of the current that comes out of + on B1, goes thru A_B. It goes thru the top R1 and the bottom R1 and thru B2, then to B1 -. Two amps out of B2 +. One amp goes to B1 - and amp goes from A to B. One amp from top R1 and one amp from A_B makes two amps thru bottom R1 and back to -B2.

10. ### geratheg Thread Starter Member

Jul 11, 2014
107
3
Thanks for the responses! Ernie, it appears you're using the voltage loop and current junction rules with 2 separate power sources. In my question the circuit is using 1 power source. Thank you for the diagrams anyway.
I think I got my answer.

ErnieM likes this.
11. ### studiot AAC Fanatic!

Nov 9, 2007
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515
Yes this is true in in the case of a single travelling wave that sum is unique.

But

In the case of a standing wave there are two solutions, similar to the answer to the question

What is √4

So yes alfacliff is correct.

Incidentally, the OP specified simultaneously. There are several circuit methods to send multiple signals along on channel, by multiplexing.

With time division multiplexing they will not be simultaneous, but with frequency division multiplexing they can be.

12. ### wayneh Expert

Sep 9, 2010
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Still not buying it as anything more than a useful abstraction. The smallest unit of charge/current is an electron, and it can only move in one direction at a time. QED

13. ### studiot AAC Fanatic!

Nov 9, 2007
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So what?
I'm sure you know as well as I do that the carriers of EM waves are photons, not electrons, which can travel in many directions at once.

Further quantum mechanics allow two electrons to occupy the same space together, provides the spins are opposite.
A gentleman called Pauli first propounded this.

Last edited: Aug 19, 2014
14. ### Lestraveled Well-Known Member

May 19, 2014
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In RF land, if the wire is one wavelength long, current will flow in one direction in the first half of the wire and the opposite direction in the second half of the wire.

15. ### wayneh Expert

Sep 9, 2010
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OK, it's beginning to sink in. Kirchoff's law doesn't apply in RF land, a very foreign place to me.

16. ### Benzodiazepine New Member

Aug 17, 2014
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Mark is correct. And AC much harder than DC.

I did AC principles in an Military prison. Wakeup time is 600 hours.
Stand up STRAIGHT as soon as you hear the alarm. Breakfast is at 700 hours.
Lunch is at 1300 hours. Dinner is at 1800 hours.

17. ### Benzodiazepine New Member

Aug 17, 2014
17
1
Kirchoff's law is a DC fundementals thing. All the voltage drops in an closed loop circuit must equal (the sum of them) -- equal the supply voltage.

18. ### wayneh Expert

Sep 9, 2010
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Oh I'm quite familiar with Kirchoff's law. What I am just now realizing is that it really isn't a "law" at all! I had thought of it like the "laws" of thermodynamics or the conservation of mass, which are pretty solid. But Kirchoff's law is out the window with RF.

I'm still not convinced that there can be electron movement - current - in two directions at the same time at a "small" scale. I do accept that charge can move in two directions in the same conductor.

19. ### Lestraveled Well-Known Member

May 19, 2014
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It is a law, you just have to know when to apply it.

20. ### THE_RB AAC Fanatic!

Feb 11, 2008
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Yes.

I can do it, but not with your circuit.

Instead I would use a very large flat conductor "wire".

Like a square sheet of aluminium foil, 1 foot square.

Then connect DC + to 2 opposite corners, and DC - to the other 2 opposite corners.

Then if you call the left side of the square A and the right side B, DC current will flow from A to B and B to A simultaneously, flowing both directions though the one conductor "wire".