Physics · Class 11 Science
Ch 1Physical World and Measurement — Class 11 Physics, concept-first.
Physics is the branch of natural science that studies matter, energy, and the fundamental interactions between them. What makes physics genuinely exciting is its enormous range: the same subject that explains how a quark behaves inside a proton (a distance of about m) also explains how galaxies orbit one another across…
Key concepts
Hover a concept to preview it and jump to its most relevant Q&A.
Nature of Physical Laws
Physicists investigate everything from sub-atomic particles to distant stars, and beyond simply recording observations, they search for the underlying laws — usually expressed as mathematical equations — that summarise t…
Most relevant Q&A
In previous exams
How often this chapter’s concepts have been examined — real appearance data, never estimated.
Chapter contents
The NCERT structure, section by section. Open a section to see its questions, then read the concept-first solution.
Scope and Excitement of Physics
Physics is the branch of natural science that studies matter, energy, and the fundamental interactions between them.
Nature of Physical Law
A physical law is a concise statement, usually written as a mathematical relation, that describes a pattern observed to hold in nature under a given set of conditions.
Physics, Technology and Society
Physics does not stay confined to the laboratory — discoveries about how nature works have repeatedly been converted into technologies that reshaped human society, often within a single generation of…
The Need for Measurement
Physics differentiates itself from purely descriptive or philosophical accounts of nature by insisting that every claim be checked against a number — obtained by comparing an unknown quantity with a f…
Units of Measurement — The SI System
Historically, different regions used different systems of units for the same physical quantities — the CGS system (centimetre, gram, second), the FPS or British system (foot, pound, second), and the M…
Measurement of Length, Mass and Time
Length is measured using different instruments depending on the scale involved:
Accuracy and Precision of Measuring Instruments
It is tempting to think that a "good" measurement is simply one made with a fine instrument, but two genuinely different qualities are actually involved:
Errors in Measurement
No measuring instrument, however well made, can determine a quantity with perfect exactness — the limitations of the instrument, the observer, and the environment always leave some uncertainty, called…
Rounding Off and Order of Magnitude
Once a calculation is done — often on a calculator that displays many more digits than any measurement actually justifies — the result must be rounded off to a number of digits consistent with the pre…
Significant Figures
Every measured value carries some uncertainty (Section 1.8), and the way that uncertainty is honestly communicated in writing is through significant figures: all the digits that are reliably known, pl…
Dimensions of Physical Quantities
Every physical quantity that is not itself one of the seven SI base quantities can be expressed as a combination of powers of the base dimensions — conventionally written as mass , length and time for…
Dimensional Analysis and Its Applications
Dimensional analysis is the technique of checking, converting, or even deriving physical relations purely by tracking the dimensions (etc.) on both sides of an equation.
Summary
- Physics studies nature across an enormous range of scales, from sub-atomic particles to galaxies, organised broadly into macroscopic and microscopic domains.
Sample & Board Papers
Sample papers and previous-year board questions for this subject.
More questions
24 Q+−Show 8 questionsHide questions8 questions
- Example 1State what is meant by saying that a physical law is “universal in nature”. Illustrate your answer with one example from mechanics and one f…Free
- Example 2List the seven SI base quantities together with their SI units and symbols. Why does the SI system use exactly seven base quantities — no mo…Free
- Example 3Using dimensional analysis, derive the dimensional formula of pressure, and hence show that pressure and mechanical stress have the same dim…Free
- Example 4A student measures the length of a rod as $4.700$ cm using a vernier caliper of least count $0.01$ cm. State the number of significant figur…Preview
- Example 5In an experiment, the acceleration due to gravity $g$ is measured five times, in m s$^{-2}$: $9.79,\ 9.82,\ 9.81,\ 9.78,\ 9.80$. Find the me…Preview
- Example 6A $12$ g sample of carbon-12 contains exactly one mole of atoms, i.e. Avogadro's number of atoms, $6.022\times10^{23}$. State the order of m…Preview
- Example 7A screw gauge has a pitch of $1$ mm and a circular scale with $100$ divisions. Calculate its least count. A wire's diameter is then read as…Preview
- Example 8Explain, with a simple example, the difference between the accuracy and the precision of a set of measurements.Preview
+−Show 11 questionsHide questions11 questions
- Q9Give two examples of how physics has directly enabled major technological developments that changed society (e.g. electricity generation, co…Free
- Q10Why do we need a standardised, internationally agreed system of units instead of letting every region use its own units of length, mass and…Free
- Q11Convert a speed of $72$ km h$^{-1}$ into m s$^{-1}$, and a speed of $5$ m s$^{-1}$ into km h$^{-1}$.Free
- Q12State whether the equation $v = u + at^2$ (where $v,u$ are velocities, $a$ is acceleration and $t$ is time) is dimensionally correct. Justif…Preview
- Q13Round off the following measurements to three significant figures: (a) $0.048625$ (b) $15.0454$ (c) $1256.5$.Preview
- Q14A systematic error and a random error both affect a measurement, but they must be treated differently. Explain the distinction between them,…Preview
- Q15The diameter of the Sun is about $1.4\times10^{9}$ m and the diameter of a hydrogen atom is about $1\times10^{-10}$ m. Estimate the order of…Preview
- Q16Using dimensional analysis, derive an expression for the time period $T$ of a simple pendulum, given that $T$ may depend on its length $l$,…Preview
- Q17A physical quantity $X$ is given by $X = \dfrac{a^2 b^3}{c\sqrt{d}}$, where $a,b,c,d$ are measured with percentage errors of $1\%,\ 3\%,\ 2\…Preview
- Q18Why is an atomic clock (based on caesium-133 transitions) considered a far more accurate time standard than a mechanical pendulum clock?Preview
- Q19Physics is often described as spanning both a “macroscopic” and a “microscopic” domain of study. Briefly describe what each domain covers, g…Preview
+−Show 5 questionsHide questions5 questions
- Q20Convert $1$ newton (the SI unit of force) into dyne (the CGS unit of force), using the unit-conversion method based on dimensions.Free
- Q21The density of a substance is $2.5\times10^{3}$ kg m$^{-3}$ in SI units. Express this density in CGS units (g cm$^{-3}$).Free
- Q22Check the dimensional correctness of the kinetic-energy relation $E_k = \tfrac12 mv^2$, and hence state the dimensional formula of energy.Preview
- Q23Two resistors, $R_1 = (4.0 \pm 0.2)\ \Omega$ and $R_2 = (6.0 \pm 0.3)\ \Omega$, are connected in series. Find the equivalent resistance toge…Preview
- Q24A cube has each edge measured as $(5.00 \pm 0.05)$ cm. Calculate the percentage error in the volume of the cube.Preview