California Science Test (CAST) 8th Grade Practice Exam

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An analog waveform has two characteristics. Which statement best describes them?

A smooth, continuous line and a rapidly changing frequency

A series of discrete steps and constant amplitude

A smooth, continuous line and a changing amplitude over time

Sharp spikes with no clear pattern

Analog waveforms are continuous in time, meaning their value exists at every moment, and they can smoothly vary in amplitude as time passes. The description that fits this best is a smooth, continuous line with amplitude changing over time, because it captures both the time-continuous nature and the changing strength of the signal. Other descriptions point to features that aren’t inherent to all analog signals: discrete steps suggest a digital or sampled signal; sharp spikes with no pattern imply noise or an irregular signal; a line with rapidly changing frequency notes a frequency change, which isn’t a defining trait of all analog waveforms.