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Total resistance of a complex circuit
The teacher here redrew the first image as the second one. That's fine. But he went on to explain why the wire marked and crossed can be omitted. I did not quite get this part. This wire is connected at 3 junctions. Let us assume them P Q and R. He says that the current in top and bottom half of the junctions are equal. But who cares? If the current in junction P = Q = R, then there should be no current flow between P Q and R right? But how can we be sure about this?