Free practice › Class 11 › Physics › Chapter 1
Units and Measurement — NEET & JEE MCQs with answers
Physical quantities are measured by comparing with internationally accepted reference standards called units; the SI system defines seven base units from which all derived units are constructed. The chapter covers significant figures, dimensional analysis, and the use of dimensions to check and derive physical relationships.
Topics in this chapter
- 1.1 Introduction
- 1.2 The International System of Units
- 1.3 Significant Figures
- 1.4 Dimensions of Physical Quantities
- 1.5 Dimensional Formulae and Dimensional Equations
- 1.6 Dimensional Analysis and its Applications
Free practice questions
In the SI definition of the kelvin, the kilogram, metre and second (in kg m$^2$ s$^{-2}$ K$^{-1}$) are themselves defined in terms of:
- A. $k$, $e$ and $N_A$
- B. $h$ and $k$ only
- C. $h$, $c$ and $\Delta\nu_{Cs}$
- D. $c$ and $\Delta\nu_{Cs}$ only
Show answer
Answer: C — NCERT Table 1.1 (kelvin): 'where the kilogram, metre and second are defined in terms of h, c and $\Delta\nu_{Cs}$.'
NCERT Class 11 Physics · Ch 1 · 1.2 The International System of Units
5.74 g of a substance occupies $1.2$ cm$^3$. Its density expressed to correct significant figures is:
- A. 4.8 g cm⁻³
- B. 4.78 g cm⁻³
- C. 5.0 g cm⁻³
- D. 4.783 g cm⁻³
Show answer
Answer: A — 5.74/1.2 = 4.783... Rounded to two significant figures (least, from 1.2) gives 4.8 g cm⁻³. (NCERT Example 1.2.)
NCERT Class 11 Physics · Ch 1 · 1.3 Significant Figures
The dimension $[A]$ in NCERT's seven-dimension scheme corresponds to which base quantity?
- A. Area
- B. Acceleration
- C. Amount of substance
- D. Electric current
Show answer
Answer: D — NCERT: electric current has dimension $[A]$ (ampere).
NCERT Class 11 Physics · Ch 1 · 1.4 Dimensions of Physical Quantities
A test of consistency of dimensions, according to NCERT, has the advantage over a test of consistency of units that:
- A. we need not commit to a particular choice of units
- B. it guarantees the equation is exactly correct
- C. it works only in the SI system
- D. it gives the numerical constants
Show answer
Answer: A — NCERT 1.6.1 states a test of dimensions tells no more nor less than a test of units, but has the advantage that we need not commit to a particular choice of units, nor worry about conversions among multiples and sub-multiples.
NCERT Class 11 Physics · Ch 1 · 1.5 Dimensional Formulae and Dimensional Equations
Apply the reasoning of Example 1.4 to the formula $K = \tfrac{1}{2}mv^{2} + m a h$, where $h$ is a height. On the basis of dimensional arguments alone, this formula:
- A. is ruled out, since two different terms have been added
- B. is ruled out, since its right side has no proper dimensions
- C. cannot be ruled out, since both terms have the dimensions $[M\,L^{2}\,T^{-2}]$
- D. is proved correct, since both terms have the dimensions of energy
Show answer
Answer: C — $[m a h] = [M][L\,T^{-2}][L] = [M\,L^2\,T^{-2}]$, the same as $[\tfrac12 mv^2]$, so the sum is allowed and has the dimensions of $K$. Formula (e) on p.9 lost its 'proper dimensions' only because $ma$ is $[M\,L\,T^{-2}]$. Passing the test does not prove a formula right (p.8), so it is merely 'not ruled out'.
NCERT Class 11 Physics Part-I · Ch 1 · 1.6.1 Checking the Dimensional Consistency of Equations · p.9
Fundamental or base units are the units assigned to the
- A. derived quantities
- B. fundamental or base quantities
- C. combinations of other units
- D. dimensionless ratios
Show answer
Answer: B — NCERT: 'The units for the fundamental or base quantities are called fundamental or base units.'
NCERT Class 11 Physics · Ch 1 · 1.1 Introduction
In the CGS system, the base units for length, mass and time were respectively:
- A. foot, pound, second
- B. centimetre, gram, second
- C. centimetre, kilogram, second
- D. metre, kilogram, second
Show answer
Answer: B — NCERT 1.2: 'In CGS system they were centimetre, gram and second respectively.'
NCERT Class 11 Physics · Ch 1 · 1.2 The International System of Units
Round off $0.104$ taken as $0.1044$ would, on reciprocal to three significant figures, retrieve which original value?
- A. 9.59
- B. 9.60
- C. 9.58
- D. 9.62
Show answer
Answer: C — NCERT: writing 1/9.58 = 0.1044 (one extra digit) and then taking the reciprocal to three significant figures retrieves the original 9.58.
NCERT Class 11 Physics · Ch 1 · 1.3 Significant Figures
According to NCERT, if an equation fails the dimensional consistency test, then it is:
- A. approximately right
- B. proved wrong
- C. correct in some units
- D. proved right
Show answer
Answer: B — NCERT 1.6.1: if an equation fails the consistency test, it is proved wrong; but if it passes, it is not proved right.
NCERT Class 11 Physics · Ch 1 · 1.5 Dimensional Formulae and Dimensional Equations
Volume is the product of length, breadth and height (three lengths). Its dimensional formula is:
- A. $[M^0 L^2 T^0]$
- B. $[M L^3 T^0]$
- C. $[M^0 L^3 T^0]$
- D. $[M^0 L^3 T^{-1}]$
Show answer
Answer: C — NCERT: dimensions of volume = $[L]\times[L]\times[L]=[L]^3=[L^3]$, with zero dimension in mass and time, i.e. $[M^0 L^3 T^0]$.
NCERT Class 11 Physics · Ch 1 · 1.4 Dimensions of Physical Quantities
Practise all 515 questions of Units and Measurement in timed NEET & JEE tests
+4/−1 marking like the real exam · see which topics cost you marks · notes, XP and leaderboards
Start your free trial →