alvan15
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I know pd between D and C is zero so no current flows from D to C, but can current flow from O to C ie is pd between C O zero? If my thinking is correct , answer should be 5R/6 if each resistor is R, can someone please explain it for me?
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uberteknik
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(Original post by alvan15)
.....can current flow from O to C ie is pd between C O zero?
Hi,

It's worthwhile attempting to redraw circuits of this nature to make analysis a little more intuitive:

Name:  Resistor matrix001.jpg
Views: 89
Size:  252.9 KB


You should now see that there are three potential dividers in parallel which means the mid points of the dividers (C, O, D) must all be at the same voltage potential if all of the resistors are identical.

Consequently, no current flows between any combination of those C, O and D junctions.

The effective resistance between A and B then becomes:

2R || 2R || 2R

R_{AB} = \left{[}\frac{1}{2R} + \frac{1}{2R} + \frac{1}{2R}\right{]}^{-1}

R_{AB} = \frac{2R}{3}
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alvan15
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(Original post by uberteknik)
Hi,

It's worthwhile attempting to redraw circuits of this nature to make analysis a little more intuitive:

Name:  Resistor matrix001.jpg
Views: 89
Size:  252.9 KB


You should now see that there are three potential dividers in parallel which means the mid points of the dividers (C, O, D) must all be at the same voltage potential if all of the resistors are identical.

Consequently, no current flows between any combination of those C, O and D junctions.

The effective resistance between A and B then becomes:

2R || 2R || 2R

R_{AB} = \left{[}\frac{1}{2R} + \frac{1}{2R} + \frac{1}{2R}\right{]}^{-1}

R_{AB} = \frac{2R}{3}
Name:  Sketch.png
Views: 83
Size:  290.9 KB
thanks for the explanation, so my idea doesnt work because p.d beween C O is the same?
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uberteknik
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(Original post by alvan15)
thanks for the explanation, so my idea doesnt work because p.d beween C O is the same?
Because there are three potential dividers between A and B, the potential difference developed at the midpoint (C, O and D) of those dividers respectively, when referenced to either A or B, must all be at exactly the same potential.

Which means the potential difference between CO or OD or CD must all be zero. No current can flow and therefore the single resistors directly connected between CO or OD, can be eliminated.
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