Physics
Physics
Problem
The current in a conductor and the potential difference across its ends are measured by an ammeter and a voltmeter. The meters draw negligible currents. The ammeter is accurate but the voltmeter has a zero error (that is, it does not read zero when no potential difference is applied). Then the zero error is (if the readings for two different conditions are 1.75 A, 14.4 V and 2.75 A, 22.4 V.) (a) 0.4 volt (b) 0.8 volt (c) -0.4 volt (d) -0.8 volt (a) 0.4 volt (b) 0.8 volt (c) -0.4 volt (d) -0.8 voltIntuitive explanation
A voltmeter with zero error reads a constant offset even when the true potential difference is zero. The key insight is that the true voltage is always the measured voltage minus this unknown offset, so you can use two different measurement pairs to set up equations and solve for the offset. Since the ammeter is accurate, the resistance must be the same in both cases—that's your constraint.
Intuitive explanation
A voltmeter with zero error reads a constant offset even when the true potential difference is zero. The key insight is that the true voltage is always the measured voltage minus this unknown offset, so you can use two different measurement pairs to set up equations and solve for the offset. Since the ammeter is accurate, the resistance must be the same in both cases—that's your constraint.