Determination of Voltage Sign:
In applying Kirchhoff’s laws to specific problems, particular attention should be paid to the algebraic signs of voltage drops and e.m.fs., otherwise results will come out to be wrong.
(a) Sign of Battery E.M.F:
A rise in voltage should be given a + ve sign and a fall in voltage should be given a −ve sign. Keeping this in mind ,it is clear that as we go from the −ve terminal of a battery to its +ve terminal, there is a rise in potential, hence this voltage should be given a + ve sign. If, on the other hand, we go from +ve terminal to −ve terminal, then there is a fall in potential, hence this voltage should be preceded by a −ve sign. It is important to note that the sign of the battery e.m.f. is independent of the
direction of the current through that branch.
Sign of IR Drop:
It is clear that the sign of voltage drop across a resistor depends on the direction of current through that resistor but is independent of the polarity of any other source of e.m.f. in the circuit under consideration.
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