In DC potentiometry for electrical measurements, which of the following tasks does not require prior standardization (calibration) of the potentiometer scale?

Introduction / Context:
DC potentiometers are precision instruments that compare unknown voltages to a reference, typically a standard cell. Before reading absolute voltages, a potentiometer is usually standardized so that the slide-wire scale reads in true volts. However, some measurement techniques use only ratios of balance lengths, which cancel the calibration constant. This question checks whether you know which applications do and do not require standardization.

Given Data / Assumptions:

• Conventional DC potentiometer with slide wire and working battery.
• Standardization sets the current so that a known length corresponds to a known voltage (for example, 1.0186 V of a Weston cell).
• Resistance can be measured by comparing two drops produced by the same current through known and unknown resistors.

Concept / Approach:
When measuring resistance R_x by the drop across R_x and a standard R_s in the same circuit current I, the potentiometer balances two voltages that are proportional to IR_x and IR_s. The balance lengths l_x and l_s are proportional to those voltages with the same scale constant k (volts per unit length). Hence R_x / R_s = (k l_x) / (k l_s) = l_x / l_s, independent of k; therefore, standardization is unnecessary. By contrast, direct EMF measurements and instrument calibration require the absolute scale in volts, so standardization is essential. Measuring current from V = IR with a standard resistor also needs the absolute voltage value, hence requires standardization.

Step-by-Step Solution:

Verification / Alternative check:

Why Other Options Are Wrong:

Common Pitfalls:

Final Answer: