NCERT Solutions for Class 11 Physics Chapter 1 Physical World and Measurement are designed to help students build a strong foundation in Physics. This chapter introduces the scope of physics, fundamental forces, physical quantities, systems of units, dimensional analysis, significant figures, and errors in measurement.
These solutions strictly follow the latest NCERT textbook and are written in a clear, exam-oriented, and student-friendly manner, making them ideal for school exams, CBSE board preparation, and competitive exams like JEE & NEET.
NCERT Solutions For Class 11 Physics Chapter 1 Units and Measurement
Q.
Fill in the blanks
(a) The volume of a cube of side 1 cm is equal to .....m3.
(b) The surface area of a solid cylinder of radius 2.0 cm and height 10.0 cm is equal to ...(mm)2.
(c) A vehicle moving with a speed of 18 kmh–1 covers....m in 1 s.
(d) The relative density of lead is 11.3. Its density is ....gcm–3 or ....kgm–3.
Q.
The unit of length convenient on the atomic scale is known as an angstrom and is denoted by Å: 1 Å = 10–10 m. The size of a hydrogen atom is about 0.5 Å. What is the total atomic volume in m3 of a mole of hydrogen atoms?
Q.
The principle of ‘parallax’ in section 2.3.1 is used in the determination of distances of very distant stars. The baseline AB is the line joining the Earth’s two locations six months apart in its orbit around the Sun. That is, the baseline is about the diameter of the Earth’s orbit ≈ 3 × 1011 m. However, even the nearest stars are so distant that with such a long baseline, they show parallax only of the order of 1’’ (second) of arc or so. A parsec is a convenient unit of length on the astronomical scale. It is the distance of an object that will show a parallax of 1’’ (second of arc) from opposite ends of a baseline equal to the distance from the Earth to the Sun. How much is a parsec in terms of metres?
Q.
Explain this common observation clearly. If you look out of the window of a fast moving train, the nearby trees, houses etc. seem to move rapidly in a direction opposite to the train’s motion, but the distant objects (hill tops, the moon, the stars etc.) seem to be stationary.
Q.
One mole of an ideal gas at standard temperature and pressure occupies 22.4 L (molar volume). What is the ratio of molar volume to the atomic volume of a mole of hydrogen? (Take the size of hydrogen molecule to be about 1 Å). Why is this ratio so large?
Q.
A famous relation in physics relates ‘moving mass’ m to the ‘rest mass’ mo of a particle in terms of its speed v and the speed of light, c. (This relation first arose as a consequence of special relativity due to Albert Einstein). A boy recalls the relation almost correctly but forgets where to put the constant c. He writes :
Q.
A book with many printing errors contains four different formulae for the displacement y of a particle undergoing a certain periodic motion:
(a = maximum displacement of particle, v = speed of particle, T = time-period of motion). Rule out the wrong formulae on dimensional grounds.
Q.
A physical quantity P is related to four observables a, b, c and d as follows:
The percentage errors of measurement in a, b, c and d are 1%, 3%, 4% and 2% respectively. What is the percentage error is the quantity P? If the value of P calculated using the above relation turns out to be 3.763, to what value should you round off the result?
Q.
The mass of a box measured by a grocer’s balance is 2.30 kg. Two gold pieces of masses 20.15 g and 20.17 g are added to the box. What is (a) the total mass of the box, (b) the difference in the masses of the pieces to correct significant figures?
Q.
The length, breadth and thickness of a rectangular sheet of metal are 4.234 m, 1.005 m and 2.01 cm respectively. Give the area and volume of the sheet to correct significant figures.
Q.
Fill in the blanks by suitable conversion of units
(a) 1 kgm2s–2 = ....gcm2s–2
(b) 1 m = ..... ly
(c) 3.0 ms–2 = .... kmh–2
(d) G = 6.67 × 10–11 Nm2(kg)–2 = .... (cm)3 s–2g–1
Q.
State the number of significant figures in the following:
(a) 0.007 m2
(b) 2.64 × 1024 kg
(c) 0.2370 gcm-3
(d) 6.320 J
(e) 6.032 Nm-2
(f) 0.0006032 m2
Q.
The photograph of a house occupies an area of 1.75 cm2 on a 35 mm slide. The slide is projected on to a screen, and the area of the house on the screen is 1.55 m2. What is the linear magnification of the projector-screen arrangement?
Q.
Answer the following :
(a) You are given a thread and a metre scale. How will you estimate the diameter of the thread?
(b) A screw gauge has a pitch of 1.0 mm and 200 divisions on the circular scale. Do you think it is possible to increase the accuracy of the screw gauge arbitrarily by increasing the number of divisions on the circular scale?
(c) The mean diameter of a thin brass rod is to be measured by vernier callipers. Why is a set of 100 measurements of the diameter expected to yield a more reliable estimate than a set of 5 measurements only?
Q.
A student measures the thickness of a human hair by looking at it through a microscope of magnification 100. He makes 20 observations and finds that the average width of the hair in the field of view of the microscope is 3.5 mm. What is the estimate on the thickness of hair?
Q.
Which of the following is the most precise device for measuring length :
(a) a vernier calipers with 20 divisions on the sliding scale
(b) a screw gauge of pitch 1mm and 100 divisions on the circular scale
(c) an optical instrument that can measure length to within a wavelength of light?
Q.
A new unit of length is chosen such that the speed of light in vacuum is unity. What is the distance between the sun and the earth in terms of the new unit of light takes 8 min and 20 s to cover this distance?
Q.
Explain this statement clearly:
“To call a dimensional quantity ‘large’ or ‘small’ is meaningless without specifying a standard for comparison”. In view of this, reframe the following statements wherever necessary:
a. atoms are very small objects
b. a jet plane moves with great speed
c. the mass of Jupiter is very large
d. the air inside this room contains a large number of molecules
e. a proton is much more massive than an electron
f. the speed of sound is much smaller than the speed of light.
Q.
A calorie is a unit of heat (energy in transit) and it equals about 4.2 J where 1 J = 1 kgm2 s–2. Suppose we employ a system of units in which the unit of mass equals α kg, the unit of length equals β m, the unit of time is γ s. Show that a calorie has a magnitude 4.2 α–1β–2γ2 in terms of the new units.
Q.
The nearest star to our solar system is 4.29 light years away. How much is the distance in terms of parsec? How much parallax would this star (named Alpha Centauri) show when viewed from two locations of the Earth six months apart in its orbit around the Sun?
NCERT Solutions For Class 11 Physics Chapter 1 Units and Measurement
NCERT Solutions for Class 11 Physics Chapter 1 – Exercise Questions
Chapter 1: Units and Measurement – Solutions
Q.1) Explain this statement clearly:
“To call a dimensional quantity ‘large’ or ‘small’ is meaningless without specifying a
standard for comparison”. In view of this, reframe the following statements wherever
necessary:
- atoms are very small objects
- a jet plane moves with great speed
- the mass of Jupiter is very large
- the air inside this room contains a large number of molecules
- a proton is much more massive than an electron
- the speed of sound is much smaller than the speed of light
Answer:
- Since a dimensionless quantity can be large or small in comparison to some standard
reference, therefore, the given statement is true. For example, the angle is a
dimensionless quantity.
θ = 60° is greater than θ = 30°, but smaller than θ = 90°.
-
- An atom is smaller as compared to the sharp tip of a pin.
- A jet plane moves with a speed greater than a superfast train.
- The mass of Jupiter is very large as compared to the mass of Earth.
- The air inside this room contains a large number of molecules as compared to that
present in one mole of air.
- The given statement is already correct.
- The given statement is already correct.
Q.2) State the number of significant figures in the following:
- 0.007 m2
- 2.64 × 1024 kg
- 0.2370 gcm-3
- 6.320 J
- 6.032 Nm-2
- 0.0006032 m2
Answer:
As per the rules of finding significant figures, the number of significant figures is given below:
- one
- three
- four
- four
- four
- four
Q.3) Explain this common observation clearly.
If you look out of the window of a fast moving train, the nearby trees, houses etc.
seem to move rapidly in a direction opposite to the train’s motion, but the distant
objects (hill tops, the moon, the stars etc.) seem to be stationary.
Answer:
The imaginary line joining an object to the eye is called the line of sight. When a train
is moving rapidly, the line of sight of a nearby house changes its direction very rapidly.
Therefore, the house seems to move rapidly in a direction opposite to the train’s motion.
Since distant objects such as the hill top, the moon, the stars, etc. are extremely large
distances apart, therefore, the line of sight does not change its direction rapidly and they
appear to be stationary.
Note: Q&A containing MathML or LaTeX or KaTeX code cannot be rendered in pdf document.
Why Use These NCERT Solutions?
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100% NCERT-aligned answers
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Clear step-by-step explanations
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Helpful for board exams & entrance exams
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Prepared by subject experts
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Frequently Asked Questions (FAQs)
Q1. Is Chapter 1 of Class 11 Physics important for exams?
Yes, this chapter forms the foundation of Physics and is crucial for understanding numericals, dimensions, and measurements used throughout the syllabus.
Q2. Are these NCERT Solutions enough for board exams?
Yes, these solutions cover all NCERT questions and are sufficient for CBSE school exams. For competitive exams, conceptual clarity from this chapter is essential.
Q3. Why is dimensional analysis important?
Dimensional analysis helps verify equations, derive relations, and convert units—making it a key scoring area.
Q4. Do questions from this chapter come in JEE and NEET?
Yes, questions related to units, errors, and dimensions frequently appear in JEE Main and NEET.
Q5. Can I download these NCERT Solutions as a PDF?
Yes, the chapter-wise PDF is available for easy offline access and revision.