Final answer:
A pendulum clock is an example of a device used to measure time, where the pendulum's full swing indicates the passage of time. Comparing the pendulum's period to the standard unit of time, the second, allows us to measure intervals accurately. Option c is the correct answer.
Step-by-step explanation:
When considering devices used to measure time, a classic example is the pendulum clock. This device measures time by taking advantage of the regular swinging motion of a pendulum. The change that indicates a change in time is the pendulum completing a full swing. When a pendulum makes one full swing, which constitutes one complete period, it indicates that a measurable interval of time has elapsed.
For instance, if we observe that a certain pendulum completes a full swing every 0.75 seconds (s), this period becomes our standard measure. The pendulum's swings can be counted, or more commonly, connected to a clock mechanism that records time on a dial.
By comparing the change observed in the pendulum's swings to the standard unit for time, the second (s), we can accurately measure time and even determine the sequence of events. Thus, in a pendulum clock, the change indicating a change in time is the pendulum completing its swing and the associated mechanism registering this swing on the clock's dial.