Q. In an experiment, a set of reading are obtained as follows - 1.24 mm, 1.25 mm, 1.23 mm, 1.21 mm. The expected least count of the instrument used in recording these readings is ______ mm.

Correct Answer: 0.01

Solution

The readings recorded in the experiment are:

1.21 mm, 1.23 mm, 1.24 mm, 1.25 mm

The smallest difference between any two consecutive readings is:

1.24 − 1.23 = 0.01 mm 1.25 − 1.24 = 0.01 mm

Since the instrument consistently records measurements differing by 0.01 mm, this value represents the minimum measurable length.

Hence, the least count of the instrument is:

0.01 mm

Therefore, the correct answer is 0.01 mm.

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