The convention for voltmeters is to use a black wire for the negative reference terminal
Chapter 2, Problem 25(choose chapter or problem)
The convention for voltmeters is to use a black wire for the negative reference terminal and a red wire for the positive reference terminal. (a) Explain why two wires are required to measure a voltage. (b) If it is dark and the wires into the voltmeter are swapped by accident, what will happen during the next measurement?
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