A voltmeter shows a reading of +2.0V when its red lead is connected to point X and its black lead to point Y in a circuit loop. Without changing the circuit, the leads are interchanged (red to Y, black to X). Which of the following best predicts the new reading and explains the result?
(a) +2.0V, because swapping leads does not affect the measured potential difference, which is always taken as positive.
(b) 0V, because Kirchhoff’s loop rule requires the algebraic sum of potential differences around the loop to be zero, so any single measurement must be zero.
(c) −2.0V, because reversing the leads reverses the direction across the element, changing the sign of the potential difference.
(d) −2.0V, because the voltmeter’s internal resistance effectively becomes negative when the leads are reversed.