Equivalent Resistence

Jun 24, 2005 3 Replies
0 0 0 0 0 0 0 0 | | | | | | | | | | | | | | | | r r r r r r r r | | | | | | | | | | | | | | | |
0---r---....---r---r---r---r---r---r---....---r---r---0 | | | | | | | | r r r r r r r r | | | | | | | | . . . . . . . . . . . . . . . . | | | | | | | | r r r r r r r r | | | | | | | |
0---r---....---r---r---r---r---r---r---....---r---r---0 | | | | | | | | r r r r r r r r | | | | | | | |
0---r---....---r---r---r---r---r---r---....---r---r---0 | | | | | | | | r r r r r r r r | | | | | | | |
0---r---....---r---r-A-r-B-r---r---r---....---r---r---0 | | | | | | | | r r r r r r r r | | | | | | | |
0---r---....---r---r---r---r---r---r---....---r---r---0 | | | | | | | | r r r r r r r r | | | | | | | |
0---r---....---r---r---r---r---r---r---....---r---r---0 | | | | | | | | r r r r r r r r | | | | | | | | . . . . . . . . . . . . . . . . | | | | | | | | r r r r r r r r | | | | | | | |
0---r---....---r---r---r---r---r---r---....---r---r---0 | | | | | | | | | | | | | | | | r r r r r r r r | | | | | | | | | | | | | | | | 0 0 0 0 0 0 0 0

This is a 2D resistive grid which expands in all directions. The potential at infinite is 0 as indicated in above schematic. Find the equivalent resistence between point A and B as shown in figure above. I found out experimentally by constructing a huge grid and applying a voltage source between A and B. Then I measured the current and took ratio of voltage and current to give me equvivalent resistence. It comes out to be approximately r/2. But how can we do it analytical. does anyone have any clue how to start? Thanks.



By inspection, it's 35 ohms.

Unless the r's are negative.

PN2222A

Regardless of r, such that r>0? I don't think so.

(1/2)*r is right.

Jon

Since you have this beast, would you mind trying a few different location pairs?

if (0,0) and (1,0) gives .500 r, as you've already said, then: (0,0) and (1,1) gives .636 r 2/PI (0,0) and (2,0) gives .726 r 2-4/PI (0,0) and (2,1) gives .773 r 4/PI-1/2 (0,0) and (2,2) gives .849 r 8/(3*PI) (0,0) and (3,0) gives .861 r 17/2-24/PI (0,0) and (3,1) gives .881 r 46/(3*PI)-4 (0,0) and (3,2) gives .924 r 4/(3*PI)+1/2 (0,0) and (3,3) gives .976 r 46/(15*PI) (0,0) and (4,0) gives .954 r 40-368/(3*PI) (0,0) and (4,1) gives .965 r 80/PI-49/2 (0,0) and (4,2) gives .992 r 6-236/(15*PI) (0,0) and (4,3) gives 1.028 r 24/(5*PI)-1/2 (0,0) and (4,4) gives 1.067 r 352/(105*PI)

It should match these values, I hope!

Jon

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