is: a circuit consisting of four electrical components (generally resistors) connecting four points (A, B, C, D, say) to form a closed loop. [P4.1]
produces: an output voltage between two non-adjacent points (A and C say) when a voltage source is connected across the other two points (B and D). [P4.1]
is used: to compare resistances. [P4.1]
is balanced: when the resistances are such that the output voltage is zero.
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