I haven't done lab work in ages, but I seem to recall both names being used to describe things we used to measure voltage. (Don't hold me to that, though!) Wikipedia has a link describing the use of a potentiometer as a voltmeter. From reading the page briefly, it sounds like the potentiometer taps off (a variable amount) of current from a circuit to measure voltage, while a voltmeter isn't variable, and is usually designed to tap off as little current as possible. Am I right in thinking this?
Erm, well, no!
A voltmeter measures voltage. The simplest form actually steals a little bit of current, and the current produces an electromagnetic deflection that is a function of the actual voltage. More sophisticated forms steal less, or almost no current at all.
A potentiometer (despite it's name) does not measure voltage, although it can produce a potential difference. It's simply a resistor with a sliding tap. The resistance between the outer terminals has a fixed value, and, depending on the position of the tap, a percentage of that resistance is presented between the tap and the outer terminals.
The Wiki reference in http://en.wikipedia.org/wiki/Voltmeter
"One may also measure voltage using a potentiometer in the null-balance method
. The potentiometer's resistance is changed at the wiper until the null detector shows zero voltage between the two circuits."
Here's how the null-balance method works.http://en.wikipedia.org/wiki/Potentiometer_(measuring_instrument
In that situation, the potentiometer is not directly measuring anything. It is producing a potential (a voltage) and the galvanometer is used to indicate when no current is flowing, which means that the potential produced from the standard voltage divided by the potential divider (the potentiometer) is the same as the unknown voltage. Assuming the resistance of the potentiometer is accurately calibrated on a dial, the unknown voltage can then be derived from the position of the potentiometer.
Can a potentiometer be used as part of a circuit
that also includes a standard voltage and a galvanometer to measure voltage? If it's properly calibrated, yes it can, as can a lot of other things.
Can a potentiometer on its own measure voltage? No it can't.
Can a voltmeter measure voltage on its own? Yes it can.