What laboratory instrument displays a graph of voltage as a function of time?

An oscilloscope is the laboratory instrument that displays a graph of voltage as a function of time. It functions by taking an input voltage signal and plotting it on a two-dimensional graph, where one axis represents voltage and the other axis represents time. This visualization allows for the observation of the waveforms of electrical signals, including their shape, frequency, amplitude, and any fluctuations over time, making it an invaluable tool for analyzing electronic circuits and signals.

In comparison, a multimeter measures electrical parameters such as voltage, current, and resistance but does not graph these measurements over time. A voltmeter is specifically designed to measure the voltage in a circuit and presents the result as a single value, rather than a continuous graph. An ammeter measures electric current and, like a voltmeter, provides a single numerical output rather than a graphical representation.