Logo
Jeeify
MCQEasyJEE 2026Significant Figures & Error Analysis

JEE Physics 2026 Question with Solution

In an experiment, a set of readings are obtained as follows: 1.24 mm, 1.25 mm, 1.23 mm, 1.21 mm.1.24~\text{mm},\ 1.25~\text{mm},\ 1.23~\text{mm},\ 1.21~\text{mm}. The expected least count of the instrument used in recording these readings is _____ mm.

  • A

    0.010.01

  • B

    0.10.1

  • C

    0.050.05

  • D

    0.0010.001

Answer

Correct answer:A

Step-by-step solution

Standard Method

Given: The recorded readings are 1.24 mm, 1.25 mm, 1.23 mm, 1.21 mm.1.24~\text{mm},\ 1.25~\text{mm},\ 1.23~\text{mm},\ 1.21~\text{mm}.

Find: The least count of the instrument.

Concept: The least count of an instrument is the smallest value it can reliably measure. It is inferred from the number of decimal places in the recorded readings.

Step 1: Observe the readings. All the readings are given correct up to two decimal places:

1.21, 1.23, 1.24, 1.251.21,\ 1.23,\ 1.24,\ 1.25

Step 2: Infer the least count. If readings are recorded up to two decimal places in millimetres, then:

Least count=0.01 mm\text{Least count} = 0.01~\text{mm}

Therefore, the correct option is A and the least count is 0.01 mm0.01~\text{mm}.

Common mistakes

  • Assuming the least count is the difference between any two consecutive readings. That is incorrect because repeated observations need not differ exactly by one least count. Instead, infer the least count from the smallest decimal place recorded.

  • Choosing 0.10.1 because the readings are around 1.21.2 to 1.31.3 mm. This is wrong because the instrument records values up to two decimal places, so the resolution is finer than 0.1 mm0.1~\text{mm}.

Practice more Significant Figures & Error Analysis questions

Get unlimited AI-adaptive practice, mastery tracking, and an AI tutor that explains every step — free to start.

Start free trialMore on Significant Figures & Error Analysis

Related questions