Final answer:
The total error in the measurement of time for a simple pendulum completing 20 oscillations with a stopwatch of 0.1 s least count is ±1.0 second. This is calculated by multiplying the number of oscillations by the least count of the stopwatch.
Step-by-step explanation:
The student is asking about the error in measuring time for a simple pendulum using a stopwatch. The time for 20 oscillations was recorded as 25 seconds, with a stopwatch having a least count of 0.1 seconds. The error in measurement of time for each oscillation is the least count since that represents the smallest interval that the stopwatch can measure. However, because we are considering a total of 20 oscillations, the total error would be 20 times the least count, which is ±1.0 second. This error allows for an uncertainty range within which the actual time measurement falls.
The SI unit for time is the second (s), and time measurements and the sequence of events are often determined using periodic events such as the swings of a pendulum. When calibrating time measurements or adjusting devices like clocks, a standard such as the SI second is utilized to ensure accuracy.