NCERT Solutions
Class 11 Physics
15 chapters · 76 important questions · Updated 2025-26
Physical World
Introduces the scope and excitement of physics, covering its fundamental forces and their relative strengths. Students learn about the scientific method and how physics underpins all natural phenomena. The chapter surveys major sub-fields of physics from mechanics to cosmology. It emphasises the unity of physics and the role of hypothesis, experiment, and theory.
Key Topics
⚠️ Deleted from Syllabus 2025-26
- — Physics, technology and society (detailed section removed from CBSE 2025-26 syllabus)
- — Detailed discussion of physicists' contributions and Nobel prizes (removed)
- — Excitement of physics — narrative portion (reduced to brief introduction only)
Important Questions
Name the four fundamental forces of nature. Which is the strongest and which is the weakest?
What do you mean by the scope of physics? Give two examples each from macroscopic and microscopic domains.
What is the principle of conservation of energy? State its universal applicability.
Distinguish between the gravitational force and the electromagnetic force in terms of their range and relative strength.
Units and Measurements
Covers the SI system of units, dimensional analysis, and significant figures. Students learn to express measurements with correct precision and use dimensional analysis for checking equations and deriving relations. Error analysis including absolute, relative, and percentage errors is a key exam topic.
Key Topics
Important Questions
What are the limitations of dimensional analysis?
The period of a simple pendulum depends on length l and acceleration due to gravity g. Using dimensional analysis, derive the formula for the time period.
The resistance R = V/I, where V = (100 ± 2) V and I = (10 ± 0.2) A. Find the percentage error in R.
Explain with an example how significant figures indicate the precision of a measurement.
Distinguish between systematic errors and random errors. How can each be minimised?
Motion in a Straight Line
Introduces kinematics of a particle moving along a straight line. Students study average and instantaneous velocity, uniform and non-uniform acceleration, and the three equations of motion. Graphical analysis using position-time and velocity-time graphs is essential for board exams.
Key Topics
Important Questions
A ball is thrown vertically upward with velocity 49 m/s. Find (i) maximum height reached, (ii) time of flight. (g = 9.8 m/s²)
Draw velocity-time graphs for uniform motion and uniformly accelerated motion. How is displacement calculated from the v-t graph?
A car starts from rest and accelerates uniformly at 2 m/s². Find its velocity and displacement after 10 s.
Define instantaneous velocity. How is it different from average velocity?
Two trains A and B are moving in the same direction with speeds 80 km/h and 50 km/h respectively. Find the velocity of train A relative to train B.
Derive the three equations of uniformly accelerated motion using the velocity-time graph.
Motion in a Plane
Extends kinematics to two dimensions using vectors. Students learn vector addition, subtraction, and resolution into components. Projectile motion and uniform circular motion are the two major applications. Relative velocity in 2D is also covered.
Key Topics
Important Questions
A projectile is launched with velocity 20 m/s at 30° to the horizontal. Find the maximum height, time of flight, and horizontal range. (g = 10 m/s²)
Prove that the trajectory of a projectile is parabolic.
Define centripetal acceleration. Derive an expression for centripetal acceleration for uniform circular motion.
Find the resultant of two vectors of magnitudes 3 N and 4 N acting at right angles to each other.
What is the angle of projection for which the horizontal range is equal to the maximum height?
Laws of Motion
Covers Newton's three laws of motion and their applications to everyday situations. Students study concepts of inertia, momentum, impulse, friction, and the dynamics of circular motion. Free body diagrams and solving problems involving multiple forces and constraints are central skills.
Key Topics
Important Questions
State Newton's Second Law of motion. How does it reduce to the First Law when F = 0?
A block of mass 5 kg is on a rough horizontal surface (μ_k = 0.3). A horizontal force of 25 N is applied. Find the acceleration. (g = 10 m/s²)
Derive the law of conservation of linear momentum from Newton's Third Law.
Explain why a person jumping from a moving bus should run in the direction of the bus after landing.
A bullet of mass 50 g moving at 400 m/s is embedded in a block of mass 950 g at rest. Find the common velocity after the collision.
What is the maximum acceleration with which a person can climb a rope if the rope can bear a maximum tension equal to 2/3 of his weight?
Work, Energy and Power
Introduces the scalar quantity work and its relationship with kinetic and potential energy. The work-energy theorem and conservation of mechanical energy are derived and applied. Elastic and inelastic collisions are analysed using energy and momentum principles.
Key Topics
Important Questions
State and prove the work-energy theorem.
A spring of spring constant 1000 N/m is compressed by 10 cm. Find the elastic potential energy stored and the velocity of a 0.5 kg block when the spring is released.
Distinguish between elastic and inelastic collisions. Give one example of each.
An engine pumps 500 kg of water per minute to a height of 10 m. Find the power of the engine. (g = 10 m/s²)
Show that in an elastic head-on collision, two equal masses exchange velocities.
System of Particles and Rotational Motion
Extends mechanics to systems of particles and rigid bodies. Concepts of centre of mass, torque, angular momentum, and moment of inertia are introduced and applied. The parallel and perpendicular axis theorems are used to calculate moment of inertia for standard shapes.
Key Topics
Important Questions
State and prove the theorem of parallel axes for moment of inertia.
A solid sphere and a hollow sphere of the same mass and radius roll down an inclined plane without slipping. Which reaches the bottom first and why?
Derive an expression for the kinetic energy of a rolling body.
Find the moment of inertia of a thin uniform rod of mass M and length L about an axis through one end perpendicular to the rod.
A diver pulls in her arms while performing a somersault. Explain using the law of conservation of angular momentum why her rate of rotation increases.
Gravitation
Covers Newton's law of universal gravitation and its applications, including satellite motion, orbital and escape velocities, and Kepler's laws. Gravitational potential energy and the variation of g with altitude and depth are also studied.
Key Topics
Important Questions
Derive an expression for the orbital velocity of a satellite. What is the orbital velocity for a satellite close to the Earth's surface? (g = 9.8 m/s², R = 6400 km)
State Kepler's laws of planetary motion. Derive Kepler's Third Law using Newton's law of gravitation.
How does acceleration due to gravity vary with (i) altitude and (ii) depth below the Earth's surface?
Calculate the escape velocity from the surface of the Earth. (g = 9.8 m/s², R = 6.4 × 10⁶ m)
What is a geostationary satellite? State two conditions for a satellite to be geostationary.
Mechanical Properties of Solids
Studies the elastic behaviour of solid materials under stress and strain. Students learn Hooke's law, Young's modulus, Bulk modulus, and Shear modulus. Stress-strain curves reveal proportionality limit, elastic limit, yield point, and breaking point.
Key Topics
Important Questions
Define Young's modulus, Bulk modulus, and Shear modulus. In which situation is each relevant?
A wire of length 2 m and cross-sectional area 10⁻⁶ m² is stretched by 1 mm under a force of 200 N. Find Young's modulus of the material.
Draw and explain the stress-strain curve for a ductile material. Mark all important points.
What is elastic fatigue? How does it affect the choice of materials in engineering?
Why are girders used in construction made in the I-shape cross-section?
Mechanical Properties of Fluids
Covers the behaviour of fluids at rest (hydrostatics) and in motion (hydrodynamics). Pressure in fluids, Pascal's law, Archimedes' principle, and Bernoulli's theorem are derived and applied. Surface tension, capillarity, and viscosity complete the chapter.
Key Topics
Important Questions
State and derive Bernoulli's theorem. List two applications of Bernoulli's principle.
A raindrop of radius 1 mm falls with terminal velocity 5 m/s. Find the coefficient of viscosity of air. (ρ_water = 10³ kg/m³, ρ_air ≈ 0)
Prove that the excess pressure inside a soap bubble is 4T/r.
Water flows through a pipe of diameter 4 cm at 2 m/s. It narrows to 2 cm diameter. Find the velocity in the narrower section.
State Archimedes' principle. A solid of mass 500 g has an apparent weight of 4.5 N when fully submerged in water. Find its volume. (g = 10 m/s²)
Thermal Properties of Matter
Covers temperature measurement, thermal expansion, specific heat, calorimetry, and modes of heat transfer. Students study linear, superficial, and volumetric expansion, latent heat, Newton's law of cooling, and the mechanisms of conduction, convection, and radiation.
Key Topics
Important Questions
A steel rod of length 1 m is heated from 20°C to 120°C. Find the increase in length. (α_steel = 1.2 × 10⁻⁵ /°C)
State Newton's law of cooling. A body cools from 80°C to 60°C in 5 minutes. How long will it take to cool from 60°C to 40°C in a room at 20°C?
Distinguish between conduction, convection, and radiation. Give two examples of each.
Define specific heat capacity and latent heat. 200 g of water at 80°C is mixed with 100 g of water at 20°C. Find the final temperature.
What is the anomalous expansion of water? What is its significance in nature?
Thermodynamics
Introduces the zeroth, first, and second laws of thermodynamics. Students study various thermodynamic processes (isothermal, adiabatic, isochoric, isobaric), heat engines, refrigerators, and the concept of entropy. Carnot's cycle and its efficiency are essential board topics.
Key Topics
Important Questions
State the first law of thermodynamics. Apply it to (i) isothermal and (ii) adiabatic processes.
Describe the Carnot cycle. Derive an expression for the efficiency of a Carnot engine.
State the second law of thermodynamics in two different ways. Show that they are equivalent.
A Carnot engine operates between 727°C and 27°C. Find its efficiency and the heat rejected to the sink for every 1000 J of heat absorbed.
What is the coefficient of performance (COP) of a refrigerator? How is it related to the efficiency of a heat engine?
Kinetic Theory
Develops the kinetic theory of gases to explain macroscopic properties (pressure, temperature, specific heat) in terms of molecular motion. Students derive the pressure of an ideal gas, the kinetic interpretation of temperature, and the law of equipartition of energy.
Key Topics
Important Questions
Derive an expression for the pressure exerted by an ideal gas using kinetic theory. Hence obtain the kinetic interpretation of temperature.
State the law of equipartition of energy. Using it, find C_v and C_p for a diatomic gas and calculate γ.
Calculate the rms speed of nitrogen molecules at 27°C. (M = 28 g/mol, R = 8.31 J mol⁻¹ K⁻¹)
What is mean free path? On what factors does it depend?
At what temperature will the rms speed of oxygen molecules be equal to the rms speed of hydrogen molecules at 300 K?
Oscillations
Covers simple harmonic motion (SHM) as a fundamental type of periodic motion. Students derive equations for displacement, velocity, and acceleration in SHM, and study simple pendulums, spring-mass systems, and energy in SHM. Damped, free, forced oscillations, and resonance are also covered.
Key Topics
Important Questions
Derive expressions for displacement, velocity, and acceleration of a particle in SHM. Show that acceleration is proportional to displacement and directed towards the mean position.
Show that total energy of a particle in SHM is constant. How does it vary with displacement?
Find the period of a spring-mass system with spring constant 200 N/m and mass 0.5 kg.
What is resonance? Give two examples of resonance — one beneficial and one harmful.
The time period of a simple pendulum is 2 s on Earth's surface. What will be its period on a planet where g is half of Earth's g?
Waves
Covers transverse and longitudinal waves, their properties, and the wave equation. Students study the superposition principle, stationary waves, normal modes in strings and pipes, and the Doppler effect. Newton's formula for speed of sound and Laplace's correction are important exam topics.
Key Topics
Important Questions
Derive Newton's formula for speed of sound in a gas. What correction did Laplace make and why?
Explain the formation of standing waves. Derive the frequencies of normal modes for a string fixed at both ends.
State the Doppler effect. Derive the general formula for apparent frequency when both source and observer are moving.
Two sound waves of frequencies 512 Hz and 516 Hz are superimposed. Find the beat frequency.
A string of length 0.5 m and linear mass density 10⁻³ kg/m is under tension 8 N. Find the fundamental frequency.
Frequently Asked Questions
Is NCERT enough for CBSE Class 11 Physics board exam?
Yes. CBSE board exams are designed entirely around NCERT. 80–90% of questions in the Class 11 Physics paper are directly based on NCERT concepts — sometimes reworded, never from outside NCERT. Completing all 76 important questions listed here is the minimum you need.
How to study NCERT Class 11 Physics for board exams?
Go chapter-by-chapter. Read the chapter first, then attempt the important questions without looking at answers. Check your answer structure — CBSE gives marks per point, so structure matters as much as content. For 5-mark answers: brief intro + 4–5 numbered points with keywords + conclusion.
Which chapters are most important in Class 11 Physics for CBSE boards?
Chapters with the most long-answer (5-mark) important questions carry the most marks in the board paper. Look at which chapters here have the highest question count — those are the ones CBSE has historically focused on. Don't skip any chapter, but spend extra time on these.
How many questions come from NCERT in CBSE Class 11 Physics exam?
Nearly all 76 questions in the Class 11 Physics board paper are rooted in NCERT. The exact question may be reworded, but the concept, definition, or formula always comes from the NCERT textbook. Practicing these 76 important questions covers the vast majority of what can be asked.