Q1.
Look at the wall clock shown in Fig. 8.9 carefully. What is the smallest interval of time you can measure with it?
Answer
One second. One second is the smallest interval of time that we can measure using this clock.
Look at what the dial of Fig. 8.9 has:
- The numbers 1 to 12 mark the hours.
- Between two numbers there are five small divisions, so the whole dial is divided into 60 small divisions.
- There are three hands — a short hour hand, a longer minute hand, and a thin, fast-moving second hand.
Second hand crosses the whole dial in 1 min = 60 s
Number of small divisions = 60
Time for the second hand to cross one division = 60 s ÷ 60 = 1 s
Number of small divisions = 60
Time for the second hand to cross one division = 60 s ÷ 60 = 1 s
Why the smallest division decides this: the smallest interval a measuring device can give you is the value of one division of its scale — just as an ordinary ruler with millimetre marks cannot measure less than 1 mm. This clock has no marks between the small divisions, so nothing shorter than 1 s can be read from it.
Did you know? A sports stopwatch reads to one-hundredth or even one-thousandth (a millisecond) of a second. That is how the winner is decided when two sprinters seem to cross the finish line together — the very thing that amazes Prerna at the start of this chapter.