Direction of current flow?

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Main Question or Discussion Point

In the following diagrams:
ll0jWm2.png


and:

0jaRP0l.png


Is current flowing horizontal or vertical&horizontal?
I'm sure for the rectangle one the flow of current is horizontal, but not sure of that square.
 

Answers and Replies

  • #2
dlgoff
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This "analogy"(?) doesn't tell me anything about current. If anything, it might suggest a higher potential in the second one.
 
  • #3
donpacino
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In both of the diagrams the current flow is both vertical and horizontal.
Assuming the voltage source has a positive value, current will flow from the voltage source into the bottom right corner of the rectangle and then to the upper left corner of the rectangle, then back around to the source.

That being said, asking if the current flow is vertical or horizontal is a very strange question.

Why do you need to know this?
 
  • #4
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This "analogy"(?) doesn't tell me anything about current. If anything, it might suggest a higher potential in the second one.
Why? It's quite simple, a voltage source connected to different shapes of conductors.
I wanted to know if they flow of current would be strictly horizontal on the first one, and both horizontal and vertical for the second.

In both of the diagrams the current flow is both vertical and horizontal.
Assuming the voltage source has a positive value, current will flow from the voltage source into the bottom right corner of the rectangle and then to the upper left corner of the rectangle, then back around to the source.
To be exact, can the direction of current be assumed like so:
8euskdz.png

And:

6fDqPud.png


Is it evenly divided, as to how some current flow vertical and some current flows horizontal(50/50)?

Why do you need to know this?
Wanted to see how the "shape" or dimensions of a conductor, and where it's connected had an effect on direction of current.
 
  • #5
davenn
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the current will flow throughout the conductor, not just in a narrow line across it
 
  • #6
NascentOxygen
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If that is a conductive medium of uniform thickness, then the current spreads out in a wide swayth, it doesn't confine its path to a thin middle strip. Think of the block as many resistances all in parallel; current goes through each, though proportionally less through the higher resistance (i.e., longer) paths.
For DC, picture a block of metal as myriad resistances in 3D. http://thumbnails111.imagebam.com/37333/4d0696373324852.jpg [Broken]
 
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  • #7
davenn
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thanks for the backup :)
 
  • #8
jim hardy
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It's like fluid flow. There'll be equipotential lines , segments of a circle centered on corners, with flow largely perpendicular
I guess that's why in my EE curriculum we had to take a course in Fluid Flow.analysis. Back in those days(slide rules) we worked them graphically like finite elements.
Only years later did i appreciate the value of that course.
 
  • #9
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the current will flow throughout the conductor, not just in a narrow line across it
If that is a conductive medium of uniform thickness, then the current spreads out in a wide swayth, it doesn't confine its path to a thin middle strip. Think of the block as many resistances all in parallel; current goes through each, though proportionally less through the higher resistance (i.e., longer) paths.
Very interesting.

If one was to assume a uniform direction there shouldn't be one right? For such conductors? Current flow will be in all directions?
I was relating such a design to applications where current has a distinguished impact. Such as the Lorentz force, if it's true that current moves around technically everywhere, there shouldn't be a unified direction. In comparison to the examples where current flow is uniformly obvious?
 
  • #10
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Initially, it felt intuitive to assume current flow was all horizontal and some parts we're vertical(around the edges), but if it goes all around... then there shouldn't be a direction for it?
It makes sense when I think of current being a scalar quantity, but when I apply some calculations, I always mistake it for a vector.
 
  • #11
dlgoff
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Why? It's quite simple, a voltage source connected to different shapes of conductors.
You didn't mention conductors in your OP. Just sayin'
 
  • #12
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You didn't mention conductors in your OP. Just sayin'
Whoops! Need to go into details next time!
 
  • #13
sophiecentaur
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Whoops! Need to go into details next time!
You certainly do - and more precision! I was initially working on the assumption that there were connections along two edges (but which ones?). It would have been much better to have no lines round the edges and a single 'blob' at the corners where the connection is made. Your drawing package will be able to do this for you.
PF is an untamed beast and will go haring off in all sorts of directions if you don't tell it exactly what to do. Then it's a helpful pussycat.
 
  • #14
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PF is an untamed beast and will go haring off in all sorts of directions if you don't tell it exactly what to do. Then it's a helpful pussycat.
. This... the true guidance!

Hm, I could adjust it now... but I think most of the members who posted get the idea for now.

But certainly will do in the future!

How about you give me you're piece about this predicament?
Why is it a predicament to me? Well, since current is somewhat all around the conductor(Literally...maybe?), does that mean there isn't a unified direction?
Specifically in relation to Lorentz force, how can it exist if current moving all around the wire?

Theory headache.
 
  • #15
donpacino
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. This... the true guidance!

Hm, I could adjust it now... but I think most of the members who posted get the idea for now.

But certainly will do in the future!

How about you give me you're piece about this predicament?
Why is it a predicament to me? Well, since current is somewhat all around the conductor(Literally...maybe?), does that mean there isn't a unified direction?
Specifically in relation to Lorentz force, how can it exist if current moving all around the wire?

Theory headache.
While the current does flow throughout all of the conductor, it will still flow from high to low voltage.
Therefore the general flow of current will be from the bottom right to the upper left.
 
  • #16
sophiecentaur
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You can also say that the equipotential lines, right next to the connectionswill be arcs of a circle. If the area is a square, (easy bit of symmetry) there will be a diagonal equipotential line across the 'other' diagonal. In the region of that diagonal, the lines will be spaced out more (lower voltage drop because of the lower effective parallel resistance) and tighter together near the connections. The shapes of the lines will morph as you move across the square.
I just can't remember the book work to do the analysis but the arm waving picture will look as I describe.
Oh yes - and the current will always flow at right angles to the equipotential lines.
 
  • #17
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While the current does flow throughout all of the conductor, it will still flow from high to low voltage.
Therefore the general flow of current will be from the bottom right to the upper left.
Great, that makes sense.

You can also say that the equipotential lines, right next to the connectionswill be arcs of a circle. If the area is a square, (easy bit of symmetry) there will be a diagonal equipotential line across the 'other' diagonal. In the region of that diagonal, the lines will be spaced out more (lower voltage drop because of the lower effective parallel resistance) and tighter together near the connections. The shapes of the lines will morph as you move across the square.
I just can't remember the book work to do the analysis but the arm waving picture will look as I describe.
Oh yes - and the current will always flow at right angles to the equipotential lines.
The wording makes sense, yet imaging it is a bit difficult, but eventually I will.
 
  • #18
sophiecentaur
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Great, that makes sense.



The wording makes sense, yet imaging it is a bit difficult, but eventually I will.
Easy peesy. Just imagine emptying a bucket full of tennis balls out at the top of a round topped hill / mound. They will all go in different directions but each one will be rolling 'downhill' taking the steepest path that it can at each point. They will all cross the contour lines at right angles. The electrical equipotential contours are exactly the same.
 
  • #19
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Little questions like these remind me of little puzz I still remember from a high school.
Goes like this: which of fish(es) in a pool will be electrocuted if two HV electric generator wires are submerged in watter at the opposite sides of the pool? Then the picture of fishies swimming in different directions in the pool was given. Anybody else heard of this puzzle?
 
  • #20
dlgoff
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Great, that makes sense.



The wording makes sense, yet imaging it is a bit difficult, but eventually I will.
Here's what the Equipotential Lines for three geometries look like that may help.

equiv.gif
 
  • #21
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Thank you all!
 
  • #22
jim hardy
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So --- using dlgoff's rightmost picture
let's think for a second about your sketch:

There'll be a minute voltage drop across any real (non-ideal) conductor.

Since current enters at lower right and exits upper left, there must be a tiny potential difference.

Draw a line made of red dashes between lower left and upper right vertices ....
Would that line represent locus of potential halfway between head and tail of your arrow?
Could your arrow represent the miniscule electric field that's moving charge ?
Would there be other electric field arrows surrounding yours, bent convex like the field lines in Don's rightmost sketch ?
Could you draw in dashed equipotential lines perpendicular to the field lines?
Could you go back to 8th grade geometry and figure out their loci? Seems to me they'd be segments of circles with centers lying on extensions of your arrow .



proxy.php?image=http%3A%2F%2Fi.imgur.com%2F6fDqPud.png


Were i any good at computer drawing i'd try it myself. Dreamed about this last night....
it was kinda fun actually, remembering my old fluid flow class and our primitive graphical solutions . Ahhh nostalgia. 1965 was a good year.

old jim
 
  • #23
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Something that I'm reminded of from another thread, is that current is a scalar, so it makes sense to have current flow moving everywhere.
But then again, how can this diagram be true?
proxy.php?image=http%3A%2F%2Fi.imgur.com%2F6fDqPud.png

Specifically in calculations that would require me to know where current is flowing, but then again it shouldn't have a direction because it's scalar, but then again the diagram is somewhat correct because of the potential difference intuitively making me assume that current will flow from bottom right to upper left as diagram above.

So I could say, current will flow as diagramed above because it will flow from high to low potentials and since the terminals are where they are... it should be like that.
 
  • #24
sophiecentaur
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Something that I'm reminded of from another thread, is that current is a scalar, so it makes sense to have current flow moving everywhere.
How can Current be a scalar? Remember Flemming's Left Hand Motor Rule? You use your finger to describe the direction of the current and that tells you the direction of the Force. If current were not a Vector quantity, you couldn't have that rule and motors wouldn't work. Just look at Ampere's Law etc. etc. ;)
 
  • #25
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Well one reason why ##I## is scalar is because it can't be added. Vectors could add up while current does not(from KCL) and there are other reasons, while as for the direction it doesn't have one, but I believe it's orientation is based on the signs in the mathematics, not so sure how to explain it well... but @vanhees71 explained it quite beautifully here, post #13.
 

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