Which instrument measures elapsed time in seconds?

• A. Stopwatch
• B. Thermometer
• C. Anemometer
• D. Pan Balance

Answer: (A)

Elapsed time means how long something lasts from start to finish. To measure it, you need a tool that starts when the event begins and stops when it ends. The stopwatch is designed for that purpose: you start timing at the moment the event starts and stop when it ends, and the display shows the duration in seconds. The thermometer measures temperature, the anemometer measures wind speed, and the pan balance measures mass. So the stopwatch directly provides elapsed time in seconds.