This isn't strictly physics, but I believe it relates enough to be relevant to this forum. I was wondering if anyone could explain to me how a potentiometer works? I'm a chem student trying to get the hang of electrochemistry, and I ran into a problem trying to understand how potentiometers relate to voltmeters. Specifically, I can't find any explanation anywhere that makes a lick of sense to me. My book explains it as follows: "When current flows through a wire, the frictional heating wastes some of the useful energy of the cell. A traditional voltmeter therefore measures a potential lower than the max cell potential. The key to determining maximum potential is to perform the measurement under conditions of zero current so that no energy is wasted. This measurement is accomplished by inserting a variable voltage device in opposition (italics--woo, that really helps) to the cell potential. The voltage on this instrument, called a potentiometer, is adjusted until no current flows into the cell circuit. Under such conditions the cell potential is equal in magnitude and opposite in sign to the voltage setting of the potentiometer. This value represents the max cell potential, since no energy is wasted heating the wire." Which leads me to ask: How does performing the measurement under zero current waste no energy in the measurement? How do you even measure a voltage with zero current? What does it mean when it says "in opposition"? I assume it's talking about a resistor. I suppose if I could only find a picture that shows this process step by step, I'd understand it. If anyone could help, I'd appreciate it.