Question

What is the device used to measure a potential difference in a circuit called?
ammeter
potentiometer
voltmeter
galvonmeter
batterymeter

Answer 1

Potential difference is measured in Volts, so something that measures potential difference is a voltmeter. You can think of electrical potential as how much potential energy a charge carrier has, and if the charged carriers on one side of a component have more energy than the charge carriers on the other side, then there is a difference in potential. Volt meters are usually place 'over' a component, measuring the energy the charge carriers have on either side.

Answer 2

VOLTMETER after VOLTA, possibly of "twitching frogs' legs" fame. (I think that VOLTAIRE, confusingly, was a French philosopher).
A "DVM" that you might find in a physics lab is a DIGITAL VOLT METER. Measures volts, and amps and ohms.
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Answer 3

ammeter potentiometer voltmeter galvonmeter batterymeter

ammeter measures current and goes in SERIES in an electric circuit. It has a low resistance so that its presence doesn't affect the current in the circuit which WOULD be there if the ammeter wasn't present (if you follow my drift).
potentiometer is a device which allows you to connect a constant voltage across two of its terminals, turn a knob, and get a varied voltage across another two of its terminals. (That's three terminals in total, 'cos generally one of the terminals is common to input and output.)
voltmeter measures voltage, goes in PARALLEL in an electric circuit and has a HIGH resistance so that it's presence doesn't affect ... as above ...
Galvanometer measure current or charge. Current in either direction through a pointer which is zeroed on a "centre zero scale". Charge when it is used BALLISTICALLY so that a pulse of current passes a charge through the G which then moves in response to the charge that has passed and gone.
I've never heard of a battery meter. COULD be a hydrometer which measures the state of a rechargeable, often heavy current duty battery, such as a car battery which has to be able to drive a the starter motor, headlights etc. When the battery is "flat", the driver may often issue and expletive as a recharger may be needed. The hydro works on the "health" of the battery being indicated by the specific gravity/relative density of the electrolyte.