NEET Physics — Units, Dimensions and Measurement

Significant Figures – Complete Notes, Revision, Important Questions & Downloads

Significant Figures governs how the precision of every measured physical quantity is reported in NEET Physics — primarily through the subtopic Rules for Counting Significant Figures, which codifies five rules: non-zero digits are always significant, trapped zeros count, leading zeros never count, trailing zeros after a decimal point count, and exponential notation strips ambiguity. NEET tests this topic directly with MCQs that ask how many significant figures does 0.00340 have (answer: 3) and indirectly through arithmetic operations where the final answer must be rounded to the correct number of significant figures. For example, if L = 2.331 cm and B = 2.1 cm, then L + B must be reported as 4.4 cm (not 4.431 cm), because addition respects the fewest decimal places.

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2 SubtopicsTheory-BasedEasy Marks

Expected QuestionsQ

1–2

Significant figures questions appear in NEET almost every year — either as direct count-the-sig-figs MCQs or as part of error-analysis numericals requiring correct rounding.

Time Required⏱

1–2 hours

One focused session to memorise the five rules plus targeted practice with 15–20 MCQs to build speed and pattern recognition.

Difficulty⚡

Easy

All five rules are mechanical — no derivation or conceptual leap required. Errors arise only from careless application, not from complexity.

NRI USA Curriculum GapUS

Low

US high-school chemistry and AP Physics both teach significant figures, but NEET places stronger emphasis on trailing-zero ambiguity and rounding rules involving the digit 5, which US curricula treat more casually.

2Subtopics

10+Practice Questions

4Free Downloads

1–2 hrsPrep Time

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NEET Weightage — Significant Figures

Units, Dimensions and Measurement (Chapter 1)

NEET Year	Questions from this Topic	Bar	Marks
2024	1	1 Q	4
2023	1	1 Q	4
2022	1	1 Q	4
2021	0	0 Q	0
2020	1	1 Q	4
2019	1	1 Q	4
6-Year Total (2019–2024)	5–7		20–28

NEET frequently asks how many significant figures in X where X contains trailing zeros or leading zeros — memorise Rules 3 and 4 as a decision pair to handle these rapidly.
Arithmetic operations (addition/subtraction) are tested by giving two measured values with different decimal precision and asking for the correctly rounded result — always round to the fewest decimal places, not fewest significant figures.
Assertion-Reason questions on significant figures are common — a typical trap states zeros are not significant as the reason, which is only partially true (trapped zeros ARE significant by Rule 2).

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Avg Questions / Year

🎯

20–28

Total Marks (6 yrs)

📈

Direct

Pattern

⚠️

Easy

Difficulty

Exam Strategy for Significant Figures in NEET Physics

Memorise the five rules as a decision tree Start every significant-figure question by asking: (1) Is the digit non-zero? → significant. (2) Is it a zero between non-zero digits? → significant. (3) Is it a leading zero before the first non-zero digit? → not significant. (4) Is it a trailing zero after a decimal point? → significant. (5) Is the number in exponential form? → count only the coefficient digits. This sequence covers every possible case. The trap: confusing rule 4 with trailing zeros WITHOUT a decimal point (e.g., 2300 is ambiguous — express as 2.300 × 10³ for 4 sig figs).

Drill the addition/subtraction vs multiplication/division distinction For addition and subtraction, the result retains the fewest DECIMAL PLACES (not significant figures) among the operands. For multiplication and division, the result retains the fewest SIGNIFICANT FIGURES. The trap: applying the multiplication rule to an addition problem — e.g., 33.3 + 3.11 + 0.313 = 36.723, but the answer must be 36.7 (one decimal place, matching 33.3), not 36.723 or 36.72.

Practise rounding with the round-to-nearest-even rule for the digit 5 When the digit to be dropped is exactly 5, round the preceding digit to the nearest even number: 2.745 rounds to 2.74 (4 is already even), and 2.735 also rounds to 2.74 (3 is odd, so it rounds up to 4). The trap: always rounding up when the dropped digit is 5, which introduces systematic bias. NEET has tested this specific rule, so practise at least 10 examples where the dropped digit is exactly 5.

Download Study Notes — Significant Figures

PDF · Cheat Sheet · MCQ Set · PYQ

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Significant Figures — Full Notes

Complete notes covering the five rules for counting significant figures, rounding-off conventions, arithmetic operation rules for significant figures, and worked NEET examples with step-by-step solutions.

2 subtopicsWorked examplesAll 5 rules

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Significant Figures — Formula Sheet

One-page quick reference: the five counting rules, addition/subtraction decimal-place rule, multiplication/division sig-fig rule, rounding conventions for digit 5, and exponential notation conversion — key rules, conditions, and one worked example per rule.

1 pageAll key rules

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Significant Figures — MCQ Practice

20 NEET-style MCQs testing identification of significant figures in numbers with leading zeros, trailing zeros, trapped zeros, and exponential notation, plus arithmetic rounding problems.

20 MCQsDetailed solutions

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Significant Figures — NEET PYQ Collection

Curated set of NEET and AIEEE previous year questions on significant figures, including assertion-reason patterns and arithmetic operation problems, with full solution breakdowns.

PYQ-basedAnswer key included

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Subtopics in Significant Figures

2-Column Table

Column A	Column B
Rules for Counting Significant Figures↗	All non-zero digits↗

Rapid Revision — Significant Figures

Concept → Trap → Example

1) Rules for Counting Significant Figures

Five Rules + Rounding

Rule 1: All non-zero digits are significant. Rule 2: Zeros between non-zero digits are significant. Rule 3: Leading zeros are never significant. Rule 4: Trailing zeros with a decimal point are significant. Rule 5: In exponential notation, only the numerical coefficient determines significant figure count.

Apply Rule 3 and Rule 4 as a pair: 0.00340 has 3 sig figs (leading zeros ignored, trailing zero after decimal counts) — NEET tests this exact pairing.
Unit conversion does not change significant figure count: 2.308 cm = 0.02308 m = 23.08 mm all have exactly 4 significant figures.
Common NEET trap: treating all zeros as non-significant. In 5.03, the zero IS significant (Rule 2: trapped between 5 and 3), giving 3 sig figs, not 2.

Example (NEET-style)Count significant figures in 0.06900: leading zeros (0.0) are not significant by Rule 3; digits 6, 9 are significant by Rule 1; trailing zeros (00) after decimal are significant by Rule 4. Total = 4 significant figures. NEET would present this alongside 6900 (ambiguous without decimal — could be 2 or 4 sig figs; use 6.900 × 10³ to specify 4).

US Curriculum Gaps — Significant Figures for NEET Physics

NRI students from US high schools may find these specific gaps when preparing for NEET Physics significant figures questions.

Trailing-Zero Ambiguity (not emphasized in AP Chemistry / AP Physics 1)

US AP courses teach significant figures but rarely test the ambiguity of trailing zeros in whole numbers without a decimal point. NEET specifically exploits this: 2300 has how many significant figures is ambiguous unless written as 2.300 × 10³ (4 sig figs) or 2.3 × 10³ (2 sig figs). US curricula typically accept either interpretation without penalty.

AP Chemistry treats 2300 as having 2 significant figures by default, whereas NEET textbooks flag it as ambiguous and require exponential notation for clarity.
NEET tests the round-to-nearest-even rule for digit 5 (e.g., 2.745 → 2.74), which most US high-school courses omit entirely.
Practice converting ambiguous whole numbers to scientific notation before determining significant figure count.

Arithmetic Operation Rules for Significant Figures (limited drill in US General Physics)

US high-school and AP Physics courses mention the rules for significant figures in arithmetic but rarely dedicate MCQs to them. NEET asks calculation questions where the key step is rounding the final answer to the correct number of decimal places (for addition) or significant figures (for multiplication).

US Physics courses focus on propagation of percentage errors rather than discrete sig-fig rules in arithmetic.
NEET requires students to distinguish addition/subtraction (fewest decimal places) from multiplication/division (fewest significant figures) in a single MCQ.
Practice chain calculations: e.g., compute area from length × breadth, then round using the operand with fewest sig figs.

Previous Year Questions — Significant Figures

4 NEET PYQ-style questions

1Taking into account significant figures, what is the value of 9.99 m − 0.0099 m?NEET 2020

9.98 m

9.9801 m

9.9 m

10.0 m

The raw subtraction gives 9.99 − 0.0099 = 9.9801 m. For subtraction, the result must be rounded to the same number of decimal places as the operand with the fewest decimal places. 9.99 has 2 decimal places; 0.0099 has 4 decimal places. The result is rounded to 2 decimal places: 9.9801 → 9.98 m. Option (b) retains all digits without rounding, violating the subtraction rule. Option (c) rounds to 1 decimal place, which is too aggressive. Option (d) rounds to the nearest integer with no justification. The correct answer is (a) 9.98 m.

2The number of significant figures in 0.0006032 m² is:NEET-style PYQ

Apply Rules 1 and 3 systematically: leading zeros (0.000) are never significant — skip them. The remaining digits are 6, 0, 3, 2. The zero between 6 and 3 is trapped between non-zero digits (Rule 2), so it IS significant. Total significant figures: 6, 0, 3, 2 = 4. Option (b) incorrectly counts one of the leading zeros. Option (c) counts all seven digits including leading zeros. Option (d) skips the trapped zero. The correct answer is (a) 4.

3Assertion (A): The number of significant figures in 0.005 is one and in 0.500 is three. Reason (R): Zeros are not significant.NEET-style Assertion-Reason

A is true, R is false

Both A and R are true, and R is the correct explanation of A

Both A and R are true, but R is not the correct explanation of A

Both A and R are false

Assertion check: 0.005 has leading zeros that are not significant (Rule 3), so only digit 5 is significant → 1 sig fig. 0.500 has leading zero not significant, but digits 5, 0, 0 are significant because trailing zeros with decimal point are significant (Rule 4) → 3 sig figs. Assertion is TRUE. Reason check: Zeros are not significant is an overgeneralisation — it holds for leading zeros (Rule 3) but fails for trapped zeros (Rule 2) and trailing zeros after decimal (Rule 4). Reason is FALSE. Correct answer is (a): A is true, R is false. Options (b) and (c) accept the reason as true, which is incorrect. Option (d) claims A is false, but the sig-fig counts in A are verified correct.

4The length, breadth, and thickness of a block are given by l = 12 cm, b = 6 cm, and t = 2.45 cm. The volume of the block according to significant figures should be:PMT 2004

1 × 10² cm³

2 × 10² cm³

1.764 × 10² cm³

176.4 cm³

Volume = l × b × t = 12 × 6 × 2.45 = 176.4 cm³. For multiplication, the result must have the same number of significant figures as the operand with the fewest sig figs. l = 12 cm has 2 sig figs; b = 6 cm has 1 sig fig; t = 2.45 cm has 3 sig figs. The limiting factor is b with 1 significant figure, so the result must be expressed to 1 sig fig: 176.4 → 2 × 10² cm³. Option (a) gives 1 × 10², which would require rounding down, but 1.764 rounds to 2 since 7 > 5. Option (c) retains 4 sig figs. Option (d) retains 4 sig figs without exponential notation. The correct answer is (b) 2 × 10² cm³.

Practice Problems — Significant Figures

Click "Reveal Answer" after attempting

1How many significant figures are in the measurement 0.310 × 10³?

👁 Reveal Answer

Option (b): 3. In exponential notation, only the numerical coefficient determines significant figures (Rule 5). The coefficient is 0.310. The leading zero before the decimal is not significant (Rule 3). Digits 3, 1 are significant (Rule 1), and the trailing zero after decimal is significant (Rule 4). So 0.310 has 3 significant figures. The power of 10 does not affect the count.

2If 97.52 is divided by 2.54, the correct result in terms of significant figures is:

38.4

38.3937

38.394

38.39

👁 Reveal Answer

Option (a): 38.4. The raw division gives 97.52 ÷ 2.54 = 38.3937... For division, the result is rounded to the fewest significant figures among the operands. 97.52 has 4 sig figs; 2.54 has 3 sig figs. The result must be expressed to 3 sig figs: 38.3937 → 38.4. Option (b) retains all calculator digits. Option (c) rounds to 5 sig figs. Option (d) rounds to 4 sig figs.

3The values 2.745 and 2.735 on rounding off to 3 significant figures will give:

2.74 and 2.74

2.75 and 2.74

2.74 and 2.73

2.75 and 2.73

👁 Reveal Answer

Option (a): 2.74 and 2.74. When the digit to be dropped is exactly 5, the round-to-nearest-even rule applies. For 2.745: the preceding digit is 4 (even), so it stays → 2.74. For 2.735: the preceding digit is 3 (odd), so it rounds up to 4 → 2.74. Both round to 2.74. Option (b) incorrectly rounds 2.745 up. Option (c) keeps 2.735 at 2.73 instead of rounding the odd 3 up. Option (d) rounds both incorrectly.

4A student measures the mass of a substance as 5.74 g and its volume as 1.2 cm³. The density, expressed with correct significant figures, is:

4.8 g/cm³

4.78 g/cm³

4.783 g/cm³

5 g/cm³

👁 Reveal Answer

Option (a): 4.8 g/cm³. Density = mass/volume = 5.74/1.2 = 4.7833... g/cm³. For division, the result takes the fewest significant figures among the operands. 5.74 has 3 sig figs; 1.2 has 2 sig figs. The result is rounded to 2 sig figs: 4.7833 → 4.8 g/cm³. Option (b) retains 3 sig figs. Option (c) retains 4 sig figs. Option (d) rounds to 1 sig fig, which is too aggressive.

5The result of 33.3 + 3.11 + 0.313, expressed with correct significant figures, is:

36.7

36.72

36.723

👁 Reveal Answer

Option (a): 36.7. The raw sum is 33.3 + 3.11 + 0.313 = 36.723. For addition, the result is rounded to the fewest decimal places among the operands. 33.3 has 1 decimal place; 3.11 has 2; 0.313 has 3. The limiting value is 33.3 with 1 decimal place, so 36.723 → 36.7. Option (b) rounds to 2 decimal places. Option (c) keeps all digits. Option (d) rounds to nearest integer.

Physics — Significant Figures Revision Checklist

Check off chapters as you revise

Use this section for quick chapter tracking before mocks, part tests, and final NEET revision.

Rules for Counting Significant Figures: Identify significant digits in numbers with non-zero digitsCount the significant figures in 42.3, 243.4, and 24.123 using Rule 1 (all non-zero digits are significant). Verify your answers: 3, 4, and 5 respectively.

Rules for Counting Significant Figures: Count trapped zeros correctlyDetermine the significant figures in 5.03, 5.604, and 4.004 using Rule 2 (zero between non-zero digits is significant). Confirm: 3, 4, and 4 respectively.

Rules for Counting Significant Figures: Recognize leading zeros as non-significantCount significant figures in 0.543, 0.045, and 0.006 by applying Rule 3 (leading zeros are never significant). Verify: 3, 2, and 1 respectively.

Rules for Counting Significant Figures: Apply trailing-zero rule with decimal pointCount significant figures in 4.330, 433.00, and 343.000 using Rule 4 (trailing zeros with decimal point are significant). Confirm: 4, 5, and 6 respectively.

Rules for Counting Significant Figures: Convert to exponential notation and count coefficient digitsExpress 1.32 × 10⁻² and 1.32 × 10⁴ in exponential form and identify that each has 3 significant figures using Rule 5 (only the numerical coefficient matters).

Frequently Asked Questions — Significant Figures

Notes · Downloads · Revision · Important Questions

What are significant figures and why do they matter in NEET Physics?

Significant figures are the reliable digits in a measured value plus the first uncertain digit. They indicate measurement precision — a value reported as 287.5 cm (4 sig figs) is more precise than 290 cm (2 sig figs). NEET tests this concept directly through MCQs asking how many significant figures a given number has, and indirectly through problems where the final numerical answer must be rounded to the correct number of sig figs.

Does changing units affect the number of significant figures?

No. The number of significant figures is independent of the unit chosen. The length 2.308 cm = 0.02308 m = 23.08 mm — all have exactly 4 significant figures. The leading zeros in 0.02308 m are placeholders caused by the unit change (Rule 3: leading zeros are not significant) and do not add precision to the measurement.

How many significant figures does a number like 2300 have?

The number 2300 written without a decimal point is ambiguous. It could have 2 sig figs (only 2 and 3 are measured, zeros are placeholders), 3 sig figs, or 4 sig figs. To remove ambiguity, express in scientific notation: 2.3 × 10³ (2 sig figs), 2.30 × 10³ (3 sig figs), or 2.300 × 10³ (4 sig figs). NEET problems avoid this by using decimal notation or exponential form.

What is the difference between significant figure rules for addition vs multiplication?

For addition and subtraction, the result is rounded to the fewest DECIMAL PLACES among the operands — e.g., 33.3 + 3.11 = 36.41, rounded to 36.4 (1 decimal place matching 33.3). For multiplication and division, the result is rounded to the fewest SIGNIFICANT FIGURES among the operands — e.g., 12 × 2.45 = 29.4, rounded to 29 (2 sig figs matching 12). Confusing these two rules is the single most common mistake in NEET sig-fig questions.

How do I round off a number when the digit to be dropped is exactly 5?

Apply the round-to-nearest-even convention (also called banker s rounding): if the preceding digit is odd, round up; if even, keep it unchanged. For example, 2.735 rounds to 2.74 (3 is odd, rounds up to 4) and 2.745 rounds to 2.74 (4 is even, stays). This convention minimises systematic rounding bias in repeated calculations. NEET has tested this specific rule in previous years.

Are the zeros in 0.500 significant?

In 0.500, the leading zero before the decimal is never significant (Rule 3). The digit 5 is significant (Rule 1). The two trailing zeros after the decimal point are significant (Rule 4: trailing zeros with a decimal point count). So 0.500 has 3 significant figures. This example appears frequently in NEET assertion-reason questions where the reason incorrectly states zeros are not significant, which is only true for leading zeros.

Can exact numbers like constants 2 or pi limit significant figures in a calculation?

No. Exact numbers — pure integers (like 2 in d = 2r), defined constants (like pi), and counting numbers — have an infinite number of significant figures. They never limit the precision of a final answer. Only measured quantities with finite precision determine the sig-fig count of a result. For example, if circumference = 2*pi*r and r = 3.14 cm (3 sig figs), the answer has 3 sig figs because the 2 and pi are exact.

How do I handle significant figures in multi-step calculations?

In multi-step calculations, retain one extra digit (called a guard digit) in all intermediate steps and round only the final answer to the correct number of significant figures. For example, to compute density = mass/volume and then multiply by a factor, carry the full calculator result through each step and apply the sig-fig rule only at the end. Rounding at each intermediate step accumulates errors that can shift the final answer.

What is the order of magnitude and how is it related to significant figures?

The order of magnitude is the power of 10 closest to a number when expressed in standard scientific notation. For example, 1.06 × 10⁻¹⁰ m has order of magnitude −10, and 1.28 × 10⁷ m has order of magnitude 7. It is distinct from significant figures: order of magnitude indicates scale while significant figures indicate precision. NEET may ask both in the same question — identify sig figs from the coefficient and order from the exponent.

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Significant Figures

Significant Figures – Complete Notes, Revision, Important Questions & Downloads

1) Rules for Counting Significant Figures

Trailing-Zero Ambiguity (not emphasized in AP Chemistry / AP Physics 1)

Arithmetic Operation Rules for Significant Figures (limited drill in US General Physics)

Physics — Significant Figures Revision Checklist

NEET NRI Counseling & Admission eBook Download

Schedule Trial Session For NEET Prep

Rules for Counting Significant Figures

All non-zero digits

Subtopics

Rules for Counting Significant Figures

All non-zero digits

NEET > Physics > Physical World and Measurement Chapters

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Significant Figures

Overview content

Significant Figures – Complete Notes, Revision, Important Questions & Downloads

1) Rules for Counting Significant Figures

Trailing-Zero Ambiguity (not emphasized in AP Chemistry / AP Physics 1)

Arithmetic Operation Rules for Significant Figures (limited drill in US General Physics)

Physics — Significant Figures Revision Checklist

NEET NRI Counseling & Admission eBook Download

Schedule Trial Session For NEET Prep

Rules for Counting Significant Figures

All non-zero digits

Subtopics

Rules for Counting Significant Figures

All non-zero digits

NEET > Physics > Physical World and Measurement Chapters

Comments

Leave a comment

Comments (0)