Physics · Units And Measurements · NEET
No. You still ADD its percentage error. This is the most common mistake. The rule for a product or a quotient is the same: sum all the percentage errors. We take the worst case (maximum error), so errors are always added, whether the quantity is on top or bottom. Example: for density = m/(pi r^2 l), the max % error = (%m) + 2(%r) + (%l). Notice r and l are in the denominator but their errors are still added.
The power becomes a multiplier for that quantity's percentage error. If a quantity has power 3, its percentage error is multiplied by 3. For P = a^3, the % error in P is 3 times the % error in a. A square root means power 1/2, so it multiplies the error by 1/2 (i.e. halves it). Example: %error of a^3 b^2 / (c sqrt(d)) = 3(%a) + 2(%b) + 1(%c) + 1/2(%d).
No, they are linked but different. Absolute error is the size of the mistake in the actual unit (like 0.001 mm). Relative error = absolute error / measured value (no unit, a fraction). Percentage error = relative error x 100. In these max-error problems you work only with percentage errors, and you combine them with the power-multiplier-and-add rule.
Percentage error = (absolute error / value) x 100. For (0.4 plus/minus 0.002) g, %error = (0.002 / 0.4) x 100 = 0.5%. Do this for every quantity first, then apply the multiply-by-power and add rule. This is exactly the step tested in NEET 2023 for density.
No. Maximum error is always a positive number because it is the largest possible spread. Options with a minus sign (like -10% or -3/13%) are traps. The answer to a maximum percentage error question is never negative.
In an experiment, the percentage errors in the measurement of physical quantities A, B, C and D are 1%, 2%, 3% and 4% respectively. Then the maximum percentage error in the measurement X, where X = A^(1/2) B^2 / (C^(1/3) D^3), will be:
A metal wire has mass (0.4 plus/minus 0.002) g, radius (0.3 plus/minus 0.001) mm and length (5 plus/minus 0.02) cm. The maximum possible percentage error in the measurement of density will nearly be:
A physical quantity P is related to four observations a, b, c and d as P = a^3 b^2 / (c sqrt(d)). The percentage errors of measurement in a, b, c and d are 1%, 3%, 2% and 4% respectively. The percentage error in the quantity P is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
For a result X = A^p B^q / (C^r D^s), the maximum percentage error = p(%A) + q(%B) + r(%C) + s(%D). Multiply each quantity's percentage error by its power and add them all, regardless of whether the quantity is in the numerator or denominator.
Maximum error is the worst possible case, where all individual errors happen to push the result in the same direction. To get this largest value, we add the magnitudes of all errors. Subtracting would give a smaller error, which is not the maximum.
NEET asks 1-2 questions almost every year from combination of errors (2019, 2023, 2025 all had one). It is a quick, guaranteed mark if you remember the multiply-by-power-then-add rule and avoid the negative-answer and denominator-subtract traps.
Maximum error adds all percentage errors directly (used in NEET). Probable or standard error combines them as a square root of the sum of squares. For NEET Class 11, always use the maximum error method: multiply by power and add.
