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infinite ladder of resistances
Each resistance in this infinite network is 1 ohm. The 'ladder' extends indefinitely to the right.
Find the total resistance between A and B.

You do not need to know any physics to do this problem. If you read the notes you will see how to write down equations for resistances of networks.

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Hold Still Please

Can you arrange a set of charged particles so that none of them start to move when released from rest?

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The NRICH Project aims to enrich the mathematical experiences of all learners. To support this aim, members of the NRICH team work in a wide range of capacities, including providing professional development for teachers wishing to embed rich mathematical tasks into everyday classroom practice.

NRICH is part of the family of activities in the Millennium Mathematics Project.

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