Sol. Let us assume, for the sake of simplicity, that the resistances of the two potentiometers are the same. When the sliding contact of each potentiometer is in the middle, the total resistance of the circuit is R 0 /2, where R 0 is the resistance of each potentiometer. If the sliding contact of the second potentiometer is in the extreme (left or right) position, we have two resistances, R 0 and R 0 /2, connected in parallel (assuming that the wires have no resistance), so that the total resistance is R =R 0 /3. The reading of the ammeter proves to be greater than when the sliding contact of the second potentiometer was in the middle position by a factor of 1.5. Thus, when the sliding contact of the second potentiometer is moved from one extreme position to the other, the readings of the ammeter pass through a minimum.