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NEET Physics Chapter Guide

NEET Physics Units and Measurements Important Questions

Revise Units and Measurements for NEET with important concepts, SI units, dimensions, significant figures, error analysis and practice MCQs with answer explanations.

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Overview Important Topics Formula Revision Important Questions Preparation Strategy FAQs
Chapter Overview

Units and Measurements for NEET Physics

Units and Measurements is an early Physics chapter, but it supports calculation-based work across the NEET syllabus. Questions commonly test SI units, dimensional formulae, significant figures, least count, percentage error and the combination of errors.

For this chapter, memorising a long list is less useful than understanding a repeatable method. First identify the physical quantity, write its dimensions using mass, length and time where needed, then check whether the final expression has the dimensions required by the question.

Study tip: Treat dimensional analysis as a checking tool. It can verify whether an equation is dimensionally consistent, but it cannot determine numerical constants or distinguish expressions that have the same dimensions.
High-yield Areas

Important Topics to Revise

Before solving NEET Units and Measurements MCQs, revise these connected areas. They cover the common reasoning patterns used in practice questions.

SI Base Units

Learn the seven base quantities and their SI units. Derived units can be expressed through base units.

Dimensions

Write dimensional formulae for force, work, power, pressure, momentum, impulse, gravitational constant and Planck constant.

Dimensional Analysis

Use it to test an equation, convert units and find relations between physical quantities.

Significant Figures

Apply rules for zeros, rounding off, multiplication, division, addition and subtraction.

Errors in Measurement

Understand absolute error, relative error, percentage error, and how errors combine in sums, products and powers.

Least Count

Know the meaning of least count and why instrument precision affects the reported measurement.

Quick Revision

Units and Measurements Formula Revision

Use this compact list before attempting a NEET Physics Units and Measurements practice test.

Force \([F] = [M L T^{-2}]\)
Work / Energy \([W] = [M L^2 T^{-2}]\)
Power \([P] = [M L^2 T^{-3}]\)
Pressure \([p] = [M L^{-1} T^{-2}]\)
Momentum \([p] = [M L T^{-1}]\)
Gravitational Constant \([G] = [M^{-1} L^3 T^{-2}]\)
Planck Constant \([h] = [M L^2 T^{-1}]\)
Percentage Error \(\text{Percentage error} = \frac{\text{absolute error}}{\text{measured value}} \times 100\)
Concept Method

How to Solve Dimensional Questions

  1. Write the formula for the quantity, if it is known.
  2. Replace each physical quantity with its dimensions in terms of \(M\), \(L\), \(T\) and other base quantities if required.
  3. Collect powers of each base quantity carefully.
  4. Match the final dimensions with the answer options.
  5. For unit conversion, use the dimensional exponents of the quantity rather than guessing from the numerical value.

For error questions, first decide whether the given quantities are added, subtracted, multiplied, divided or raised to a power. The error rule depends on that operation.

Practice MCQs

NEET Physics Units and Measurements Important Questions

Try these practice questions first. Open the answer explanation only after attempting each question yourself.

Question 1 · Dimensions

The dimensional formula of pressure is:

A. \([M L T^{-2}]\)
B. \([M L^{-1} T^{-2}]\)
C. \([M L^2 T^{-2}]\)
D. \([M L^{-1} T^{-1}]\)
Show answer and explanation

Answer: B. Pressure is force divided by area. Since force has dimensions \([M L T^{-2}]\) and area has dimensions \([L^2]\), pressure has dimensions \([M L^{-1} T^{-2}]\).

Question 2 · Significant Figures

How many significant figures are present in 0.004050?

A. 2
B. 3
C. 4
D. 5
Show answer and explanation

Answer: C. Leading zeros are not significant. The digits 4, 0, 5 and the final 0 are significant, so the number has four significant figures.

Question 3 · Error Analysis

If \(Q = A \times B\), and the percentage errors in \(A\) and \(B\) are 2% and 3% respectively, the maximum percentage error in \(Q\) is:

A. 1%
B. 5%
C. 6%
D. 12%
Show answer and explanation

Answer: B. For multiplication, maximum fractional or percentage errors add. Therefore, percentage error in \(Q\) is \(2\% + 3\% = 5\%\).

Question 4 · Dimensional Consistency

Which relation is dimensionally correct for a body moving with initial velocity \(u\), acceleration \(a\), and time \(t\)?

A. \(v = u + at\)
B. \(v = u + a/t\)
C. \(v = u + at^2\)
D. \(v = u + t/a\)
Show answer and explanation

Answer: A. Velocity has dimensions \([L T^{-1}]\). Acceleration multiplied by time gives \([L T^{-2}] [T] = [L T^{-1}]\), which matches velocity.

Question 5 · Derived Units

The SI unit of impulse is equivalent to:

A. N/m
B. N·s
C. N/m²
D. J/s
Show answer and explanation

Answer: B. Impulse equals force multiplied by time, so its SI unit is newton-second. It also has the same dimensions as momentum.

Question 6 · Unit Conversion

If 1 newton = \(10^5\) dyne, then 1 joule is equal to:

A. \(10^5\) erg
B. \(10^6\) erg
C. \(10^7\) erg
D. \(10^8\) erg
Show answer and explanation

Answer: C. One joule is one newton-metre. Since 1 N = \(10^5\) dyne and 1 m = \(10^2\) cm, 1 J = \(10^5 \times 10^2\) dyne-cm = \(10^7\) erg.

Question 7 · Errors

A length is measured as \((5.0 \pm 0.1)\) cm. The percentage error in the measurement is:

A. 0.2%
B. 1%
C. 2%
D. 5%
Show answer and explanation

Answer: C. Percentage error = \((0.1/5.0) \times 100 = 2\%\).

Question 8 · Significant Figures

When 12.11 and 18.0 are added, the result should be reported as:

A. 30.11
B. 30.1
C. 30
D. 30.110
Show answer and explanation

Answer: B. In addition and subtraction, the answer is reported to the least number of decimal places among the values. Since 18.0 has one decimal place, \(12.11 + 18.0 = 30.1\).

Ready for More NEET Physics Practice?

Use chapter-wise tests after revision and full-length mock tests after covering several chapters. Reviewing incorrect answers is usually more valuable than immediately taking another test.

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Preparation Strategy

How to Prepare Units and Measurements for NEET

  1. Memorise SI base units and a small set of frequently used dimensional formulae.
  2. Practise writing dimensions from standard Physics equations instead of learning every formula separately.
  3. Solve separate sets for significant figures and error propagation because small rule mistakes are common.
  4. Keep a one-page revision sheet for powers of \(M\), \(L\), and \(T\) in common quantities.
  5. Attempt timed MCQs and review why each wrong option is incorrect.

Common mistakes to avoid

  • Counting leading zeros as significant figures.
  • Using the addition-error rule for multiplication or division.
  • Forgetting to square or cube the percentage error when a quantity has a power.
  • Assuming dimensional correctness proves that a formula is physically complete.
  • Using old exam-pattern information without checking the current official notice.
FAQs

NEET Units and Measurements FAQs

Is Units and Measurements important for NEET Physics?

Yes. The chapter is useful both for direct questions and for checking calculations in other Physics topics. Focus on dimensional formulae, significant figures and errors.

What are the most important topics in Units and Measurements?

SI units, dimensions, dimensional analysis, significant figures, absolute error, relative error, percentage error and least count are important revision areas.

Can dimensional analysis derive every Physics formula?

No. It can help check dimensional consistency or obtain the form of some relations, but it cannot give dimensionless constants or completely derive every physical equation.

How should I revise significant figures for NEET?

Learn the zero rules first, then practise rounding after addition, subtraction, multiplication and division. Short daily practice is often more effective than one long session.

Are these questions official NEET previous-year questions?

No. The questions on this page are original practice questions created for revision. Use official sources separately when checking exact previous-year papers and current examination information.