If a two-port network is passive, then we have, with the usual notation, the following relationship

Superposition principle is not applicable to a network containing time-varying registors.

A precise measurement guarantees accuracy of the measured quantity.

A d.c. potentiometer is designed to measure up to about $$2$$ $$V$$ with a slide wire of $$800$$ mm. A standard cell of emf $$1.18V$$ obtains balance at $$600$$ mm. A test cell is seen to obtain balance at $$680$$ mm. The emf of the test cell is