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Exam level4 past questions

Errors in measurement

Study the types of errors in physical measurements, their classification, and how errors propagate in calculations and experiments.

Why this shows up in the exam

NEET expects you to identify, calculate, and minimize errors in experimental data and derived results.

How NEET tests this

Numerical · 4 QsDirect recall

Learn the idea

Errors in measurement tell how far an observed value may deviate from the true value. The key insight is that the relative (percentage) error is obtained by dividing the average absolute deviation by the mean of the observations and multiplying by 100.

🧠 Memory hook: MAD = Mean Average Deviation – think of ‘M’ for Mean, ‘A’ for Average, ‘D’ for Deviation, all together give the error you need.

Get this one clearly and it pays off every single time it shows up in the paper. 🎯

Formulas & facts to keep ready

  • Absolute error = |observed – true| (or deviation from mean for a set)
  • Relative error = (absolute error / true value) × 100 %
  • Mean of a set = Σ values / number of values
  • Mean absolute deviation = Σ|xi – mean| / N

How to approach it

  1. 1Find the arithmetic mean of all the readings
  2. 2Compute the absolute deviation of each reading from the mean and take their average (mean absolute deviation)
  3. 3Divide this average deviation by the mean and multiply by 100 to get percentage relative error

Worked example — watch it click

Time intervals measured by a clock give the following readings: 1.25 s, 1.24 s, 1.27 s, 1.21 s and 1.28 s. What is the percentage relative error of the observations?

  • A)2%
  • B)4%
  • C)16%
  • ✅1.6%

The concept behind this problem

The problem asks for the percentage relative error, so you must calculate the mean, the average of the absolute deviations from that mean, and then form the ratio as prescribed by the definition of relative error.

Step by step

  1. 1Mean = (1.25 + 1.24 + 1.27 + 1.21 + 1.28)/5 = 6.25/5 = 1.25 s.
  2. 2Mean absolute deviation = (0 + 0.01 + 0.02 + 0.04 + 0.03)/5 = 0.10/5 = 0.02 s.
  3. 3Relative error = (0.02/1.25) × 100 = 1.6%.

Watch out

Students often replace the mean absolute deviation with the standard deviation or with the simple range, leading to a wrong percentage.

Common slip-ups that cost marks

  • •Using the range (max‑min) instead of mean absolute deviation
  • •Dividing by the sum of readings instead of the mean
  • •Keeping extra decimal places that change the final percent
  • •Confusing relative error with percent uncertainty

🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.

Practise it

These are real questions from past NEET papers that test this exact idea.

Question 1 of 4NEET 2021

In an experiment, the percentage of error occurred in the measurement of physical quantities A, B, C and D are 1%, 2%, 3% and 4% respectively. Then the maximum percentage of error in the measurement X, where X = A²B¹/² / C¹/³D³, will be:

Push further

More challenging

2 harder questions built from the past papers above — a step up in difficulty, with distractors designed so you can't get there by elimination. Written and checked by our reviewers, not from a real paper.

Question 1 of 2

A physical quantity Q is given by Q = A²B / C^(1/2). The percentage errors in the measurement of A, B, and C are 1%, 2%, and 4% respectively. What is the percentage error in Q?

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