An Enginner Cannot Reproduce This Problem

Alice has a box with many identical 1 Ω 1 \Omega resistors and she decides to arrange them in an infinite triangular lattice (a portion is shown in the above figure). She is interested in the electrical properties of this triangular mesh. She uses an Ohmmeter to determine the equivalent resistance between points A and B.

What is the Ohmmeter's in Ohms reading?.


The answer is 0.33.

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3 solutions

Discussions for this problem are now closed

Tanay Kibe
Apr 21, 2014

The problem can be solved by superposition.

Inject I current at point A. There are 6 branches at A and hence by symmetry, each branch will carry a current of I/6 This is the first case.

Now remove I current from point B. Using the same argument as above, the branch AB carries a current of I/6

Superpose the above cases. Hence effectively the branch AB carries a current of I/3

The resistance of AB is 1 hence the resistance of the remaining circuit is 0.5

AB and the remaining circuit are in parallel and hence the equivalent resistance is 0.333

Can we do it like this?? It seems too odd.......

Jitesh Mittal - 7 years, 1 month ago

that just blew my mind.. Thanks for the great explaination

Jeet Dutta - 7 years, 1 month ago

cudnt have said it any better.

Rafey AK - 7 years, 1 month ago
Sudipan Mallick
Apr 22, 2014

i assume that there is a battery emf v0 connected between pts A nd B. if current supplied by the battery is I then by symmetry current in all wires will b same. since a triangle has three sides current will b 1/3rd of each line. so; v0=i0Req v0=i0/3R0 i0Req=i0/3R0 Req=R/3.

wow u r genius!!! :D

Arijit Banerjee - 7 years, 1 month ago
Vishnudatt Gupta
May 17, 2014

(Assume a battery is connected b/w A&B) now assume that a current of 6A enters at point A, it

gets distributed along each resistor as 1A(symmetry)....now assume at point B...6A current

comes out. thus the resistor AB will have a -ve 1A current in it...using superposition theorem the

net current in AB is 2A, the voltage drop across AB is 2V while total current in the circuit is

6A...the equivalent resistance= 2A/6V=1/3 Ohms

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