Electrical Instruments

N/A

In this scenario, we have three resistors of equal value connected in a triangular arrangement. We know the voltage across AB is . The total resistance between A and B, and A and C can be found by recognizing that in a triangle, the total resistance between two points is given by the sum of the resistances in the paths through the network. The current splits evenly between the two paths (since all resistors are identical). Therefore, the ratio of the current through AB to ACB is .
Thus, the correct answer is .

Concept:
Physics - Electrical Measuring Instruments.
Step 1: Compare Voltmeter vs. Potentiometer.
A standard voltmeter must draw a small amount of current to move its needle or activate its sensor. This current slightly changes the potential difference it is trying to measure.
Step 2: Analyze the "Null Point" principle.
A potentiometer works on the principle of balancing an unknown EMF against a known potential difference. When the galvanometer shows zero deflection (the "null point"), no current flows between the two circuits.
Step 3: Relate to ideal measurement.
Because it draws zero current from the test source at the moment of measurement, it effectively acts as a voltmeter with infinite resistance. This allows it to measure the \textit{actual} EMF of a cell, rather than just the terminal voltage.
Step 4: Conclusion.
Its "ideal" status comes from not drawing current from the source at the null point.