Potentiometer Basic Proportionality — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Potentiometer Basic Proportionality This relationship holds true when the potential drop across two resistances ( R and X ) is measured using a potentiometer wire of uniform resistance, and the potential drop is directly proportional to the length of the wire segment. The potential drop ( V ) across a resistance ( R ) is proportional to the length ( l ) of the wire segment: V l . The potential drop is also proportional to the resistance: V R . Therefore, the ratio of resistances must equal the ratio of the corresponding lengths: R X = l 100 - l . This principle is used to measure unknown resistances accurately by balancing the potential drop. 0 < l < 100 The wire resistance must be uniform. Assuming the ratio of resistances is equal to the ratio of the resistances themselves (ignoring the length proportionality). Confusing the proportionality constant (the wire's resistance per unit length) with the actual resistance values. Assuming the relationship is linear when plotting R vs l (it is linear, but the ratio is the key concept).