Course Content
Class 11 Physics Chapter 4 Motion In A Plane
4 Motion in a plane 4.1 Introduction 4.2 Scalars and vectors 4.3 Multiplication of vectors by real numbers 4.4 Addition and subtraction of vectors – graphical method 4.5 Resolution of vectors 4.6 Vector addition – analytical method 4.7 Motion in a plane 4.8 Motion in a plane with constant acceleration 4.9 Relative velocity in two dimensions 4.10 Projectile motion 4.11 Uniform circular motion
Class 11 Physics Chapter 5 Laws of motion
Section Name Topic Name 5 Laws of motion 5.1 Introduction 5.2 Aristotle’s fallacy 5.3 The law of inertia 5.4 Newton’s first law of motion 5.5 Newton’s second law of motion 5.6 Newton’s third law of motion 5.7 Conservation of momentum 5.8 Equilibrium of a particle 5.9 Common forces in mechanics 5.10 Circular motion 5.11 Solving problems in mechanics
Class 11 Physics Chapter 6 Work Energy and Power
Section Name Topic Name 6 Work Energy and power 6.1 Introduction 6.2 Notions of work and kinetic energy : The work-energy theorem 6.3 Work 6.4 Kinetic energy 6.5 Work done by a variable force 6.6 The work-energy theorem for a variable force 6.7 The concept of potential energy 6.8 The conservation of mechanical energy 6.9 The potential energy of a spring 6.10 Various forms of energy : the law of conservation of energy 6.11 Power 6.12 Collisions
Class 11 Physics Chapter 7 Rotation motion
Topics Introduction Centre of mass Motion of COM Linear Momentum of System of Particles Vector Product Angular velocity Torque & Angular Momentum Conservation of Angular Momentum Equilibrium of Rigid Body Centre of Gravity Moment of Inertia Theorem of perpendicular axis Theorem of parallel axis Moment of Inertia of Objects Kinematics of Rotational Motion about a Fixed Axis Dynamics of Rotational Motion about a Fixed Axis Angular Momentum In Case of Rotation about a Fixed Axis Rolling motion
Class 11 Physics Chapter 9 mechanics properties of solid
Section Name Topic Name 9 Mechanical Properties Of Solids 9.1 Introduction 9.2 Elastic behaviour of solids 9.3 Stress and strain 9.4 Hooke’s law 9.5 Stress-strain curve 9.6 Elastic moduli 9.7 Applications of elastic behaviour of materials
Class 11 Physics Chapter 11 Thermal Properties of matter
Section Name Topic Name 11 Thermal Properties of matter 11.1 Introduction 11.2 Temperature and heat 11.3 Measurement of temperature 11.4 Ideal-gas equation and absolute temperature 11.5 Thermal expansion 11.6 Specific heat capacity 11.7 Calorimetry 11.8 Change of state 11.9 Heat transfer 11.10 Newton’s law of cooling
Class 11 Physics Chapter 14 Oscillations
Section Name Topic Name 14 Oscillations 14.1 Introduction 14.2 Periodic and oscilatory motions 14.3 Simple harmonic motion 14.4 Simple harmonic motion and uniform circular motion 14.5 Velocity and acceleration in simple harmonic motion 14.6 Force law for simple harmonic motion 14.7 Energy in simple harmonic motion 14.8 Some systems executing Simple Harmonic Motion 14.9 Damped simple harmonic motion 14.10 Forced oscillations and resonance
Class 11th Physics Online Class For 100% Result
About Lesson


What is Kinetic Theory?

  • Kinetic theory explains the behaviour of gases based on the idea that the gas consists of rapidly moving atoms or molecules.
  • In solids the molecules are very tightly packed as inter molecular space is not present In liquids inter molecular spaces are more as compared to solids and in gases the molecules are very loosely packed as intermolecular spaces are very large.
  • The random movement of molecules in a gas is explained by kinetic theory of gases.
  • We will also see that why kinetic theory is accepted as a success theory.
  • Kinetic theory explains the following:-
  • Molecular interpretation of pressure and temperature can be explained.
  • It is consistent with gas lawsand Avogadro’s hypothesis.
  • Correctly explains specific heat capacities of many gases.

Molecular nature of matter

John Dalton

  • Atomic hypothesis was given by many scientists. According to which everything in this universe is made up of atoms.
  • Atoms are little particles that move around in a perpetual order attracting each other when they are little distance apart.
  • But if they are forced very close to each other then they rebel.
    • For example: – Consider a block of gold. It consists of molecules which are constantly moving.
  • Dalton’s atomic theory is also referred as the molecular theory of matter.This theory proves that matter is made up of molecules which in turn are made up of atoms.
  • According to Gay Lussac’s law when gases combine chemically to yield another gas,their volumes are in ratios of small integers.
  • Avogadro’s law states that the equal volumes of all gases at equal temperature and pressure have the same number of molecules.
  • Conclusion: – All these laws proved the molecular nature of gases.
  • Dalton’s molecular theory forms the basis of Kinetic theory.

Why was Dalton’s theory a success?

  • Matter is made up of molecules, which in turn are made up of atoms.
  • Atomic structure can be viewed by an electron microscope.

Solids, Liquids, Gases in terms of molecular structure

Basis of Difference Solids Liquids Gases
Inter Atomic Distance(distance between molecules). Molecules are very tightly packed.  Inter atomic distance is minimum. Molecules are not so tightly packed. Inter atomic distance is more as compared to solids. Molecules are loosely packed .Free to move. Inter atomic distance is maximum.
Mean Free Path is the average distance a molecule can travel without colliding. No mean free path. Less mean free path. There is mean free path followed by the molecules.
Kinetic Theory Notes

Behaviour of Gases

  • Gases at low pressures and high temperatures much above that at which they liquify (or solidify) approximately satisfy a relation between their pressure, temperature and volume:
    • PV=KT (i)
    • This is the universal relation which is satisfied by all gases.
      • where P, V, T are pressure,volume and temperature resp. and
      • K is the constant for a given volume of gas. It varies with volume of gas.
    • K=NkB where
      • N=number of molecules and
      • kB = Boltzmann Constant and its value never change.
    • From equation (i) PV= NkB
    • Therefore PV/NT = constant=(kB)(Same for all gases).
    • Consider there are 2 gases :- (P1,V1,T1) and (P2, V2,T2) where P, V and T are pressure, volume and temperature resp.
    • Therefore P1,V1/(N1T1) = P2V2/(N2T2)
    • Conclusion: – This relation is satisfied by all gases at low pressure and high temperature.

= (11.143×105x30x10-3)/ (8.314×290)

= 13.86

But, n2 = m2/M Where, m2 is the mass of oxygen

remaining in the cylinder m2 = n2M = 13.86 × 32

= 453.1 g

The mass of oxygen taken out of the cylinder is given by the relation:

Initial mass of oxygen in the cylinder – Final mass of oxygen in the cylinder

= m1 – m2

= 584.84 g – 453.1 g

= 131.74 g

= 0.131 kg

Therefore, 0.131 kg of oxygen is taken out of the cylinder.

Problem:- An air bubble of volume 1.0 cm3 rises from the bottom of a lake 40 m deep at a temperature of 12 °C. To what volume does it grow when it reaches the surface, which is at a temperature of 35 °C?

Answer:- Volume of the air bubble, V1 = 1.0 cm3 = 1.0 × 10–6 m3

Bubble rises to height, d = 40 m

Temperature at a depth of 40 m, T1 = 12°C = 285 K

Temperature at the surface of the lake, T2 = 35°C = 308 K

The pressure on the surface of the lake:

P2 = 1 atm = 1 ×1.013 × 105 Pa

The pressure at the depth of 40 m:

P1 = 1 atm + dρg Where, ρ is the density ofwater = 103 kg/m3 g is the acceleration due

to gravity = 9.8 m/s2

Therefore, P1 = 1.013 × 105 + 40 × 103 × 9.8 = 493300 Pa

We have: P1 V1/T1 = P2V2/T2

Where, V2 is the volume of the air bubble when it reaches the surface

V2 = P1 V1T2/T1P2

= (493300) (1.0×10-6)308/(285×1.013×105)

= 5.263 × 10–6 m3 or 5.263 cm3

Therefore, when the air bubble reaches the surface, its volume becomes 5.263 cm3.

Justification of the Avogadro’s hypothesis from equation of gas

  • Avogadro’s hypothesis states that equal volumes of all gases at equal temperature and pressure have the same number of molecules.
  • Consider the equation PV/NT = constant and if P,V and T are same for 2 gases then N(number of molecules) is also same.
  • According to Avogadro’s hypothesis number of molecules per unit volume is same for all gasesat a fixed P and T.
  • Avogadro number is denoted by NA. WhereA denotes Avogadro number.
  • NA = 6.02×1023. It is universal value.
  • Experimentally it has been found that the mass of 22.4 litres of any gas is equal to molecular weight in grams at standard temperature and pressure.
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