Cube of Resistors

Twelve resistors of resistance 1Ω are arranged in such a way that they form a cube, as shown in the image. Find the resistance between points A and B on the cube.

Just to make it more clear, all the resistors are of the same value 1 Ω . 1 \Omega .

6/5 5/3 5/6 3/5

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1 solution

Mark Hennings
Mar 17, 2016

By symmetry, the three vertices adjacent to A A are equipotentials, and so can be coalesced. Similarly, the thee vertices adjacent to B B are equipotentials, and so can be coalesced.

The resulting circuit consists of a series of three 1 Ω 1\,\Omega resistors in parallel, followed by six 1 Ω 1\,\Omega resistors in parallel, followed by three 1 Ω 1\,\Omega resistors in parallel, giving a total effective resistance of 1 3 + 1 6 + 1 3 = 5 6 Ω \tfrac13 + \tfrac16 + \tfrac13 = \boxed{\tfrac56\,\Omega} .

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