Which statement best describes what an oscilloscope displays when examining a time-domain signal?

• A. Phase versus frequency.
• B. Time difference between two signals.
• C. Voltage as a function of time.
• D. The average value of the signal.

Answer: (C)

An oscilloscope shows how voltage changes over time. In a time-domain view, the vertical axis represents voltage and the horizontal axis represents time, so the trace is literally voltage as a function of time. This lets you see the shape of the waveform, its amplitude, how often it repeats (the period), and how the signal evolves moment by moment.

This is different from a frequency-domain view, which would plot something like phase or amplitude versus frequency. You can use the display to estimate frequency by measuring the period of a waveform, and you can measure the time difference between signals with cursors, but the primary display is voltage versus time. The average value isn’t the default display; you’d compute or read it separately if needed, though a DC level can appear if the signal has one.