Differences between Voltmeters and Ammeters
A voltmeter must be connected in parallel to measure the voltage of a device because objects in parallel experience the same potential difference. A voltmeter is used to measure the electrical potential difference between two locations in an electrical circuit. Voltmeter and ammeter are used to measure electric current and voltage. A voltmeter measures the voltage of a circuit, while the ammeter, which gets its name from the unit for electric current, amperes, measures the current of a circuit. The ammeter must be connected to a device in series because objects in a series experience the same current. The devices cannot be connected to a voltage source because ammeters are designed to work under minimal burden. Burden refers to the voltage drop across the ammeter, normally a very small fraction of a volt.