This article is formulated according to the chapter in the NCERT Syllabus of 11th Std Physics OR 1st PUC Physics.


Science is organized, systematic, and formulated knowledge obtained through observations, experiments, and verifications.

Note: The word Science originates from the Latin verb “SCIENTIA”, which means “to know”.

Scientific method

The procedure followed in acquiring knowledge in science is called the scientific
It involves the major steps, which are,
(i) Systematic observation.
(ii) Logical reasoning.
(iii) Model making.
(iv) Theoretical prediction.
(v) Verification OR Rejection of theory.


Law is a statement given based on observation, experimentation, and analysis.
Ex: Newton’s laws of motion.


The behavior of the physical system is explained in terms of a set of a minimum number of laws called Theory.

Ex: Ptolemy’s geocentric theory.

Branches of Science

There are two main branches of science, 1) Physical science and 2) Biological science.

The main branches of Physical science are, 1) Physics and 2) Chemistry.


The term Physics is derived from the Greek word called “FUSIS”, which means “Nature”. Physics is a branch of science that deals with the study of Nature and Natural phenomena. Two principal thrusts are physics are (i) Unification and (ii) Reduction.


It is an effort to see a physical world as the manifestation of some universal law in different domains and conditions. Ex: (a) Isaac Newton unified celestial and terrestrial mechanics and showed that the same laws of motion and law of gravitation apply to both domains. (b) Hans Christian Oersted and Michel Faraday showed that electric and magnetic phenomena are inseparable aspects of a unified domain. (c) James Clerk Maxwell unified electricity, magnetism, and optics, showing that light is an electromagnetic wave.


Explaining the properties of complex systems using the properties and interactions of their constituent simpler parts is called reductionism. Ex: Initially thermodynamics was dealing with a bulk system in terms of temperature, internal energy, etc. Now the kinetic theory and statistical mechanics interpreted these quantities in terms of properties of molecular constituents of the bulk system.

Scope of physics

The scope of physics is very broad and covers a wide range of many branches. It is studied under the following headings.

(i) Classical mechanics: The branch concerned with the motion of objects moving at speeds very small compared to the speed of light.

(ii) Thermodynamics: The branch dealing with heat, temperature, and work.

(iii) Electrodynamics: It deals with electricity, magnetism, and electromagnetic fields.

(iv) Quantum mechanics: The study of motion in the micro world of atoms is known as quantum mechanics.

(v) Optics: It is the branch of physics that deals with the nature of light and the different properties and phenomena exhibited by light.

(vi) Relativity: It describes the motion of the objects moving at any speed, even at speeds approaching the speed of light in a vacuum.

Totally physics deals with the macroscopic world like galaxies and the universe as well as the microscopic world like the nucleus of an atom and fundamental particles like electrons, protons, neutrons, etc.

The excitement of Physics

The study of physics is quite interesting and exciting. In physics, we come across a wide range of mass, length, and time. But despite the wide range of the order of these physical quantities, it is possible to understand them quite easily. This is the reason for the excitement in physics. Physics, technology, and society


The application of scientific knowledge for practical purposes is called Technology. Technologists use the information or knowledge of physics for designing the various applications and other instruments which help to make our material way of life comfortable.

A few advancements in technology based on physics

TechnologyScientific principle(s)
Steam engineLaws of thermodynamics
Nuclear reactorControlled nuclear fission
Radio and TelevisionGeneration, propagation, and detection of electromagnetic waves
LasersLight amplification by stimulated emission of radiation
Production of ultra-high magnetic fieldsSuperconductivity
Rocket propulsionNewton’s laws of motion
Electric generatorFaraday’s laws of electromagnetic induction
Hydroelectric powerConversion of gravitational potential energy into electrical energy
AeroplaneBernoulli’s principle in fluid dynamics
Particle acceleratorsThe motion of charged particles in electromagnetic fields
SonarReflection of ultrasonic waves
Optical fibersTotal internal reflection of light
Non-reflecting coatingsThin film optical interference
Electron microscopeWave nature of electron
PhotocellPhotoelectric effect
Fusion test reactor (Tokamak)Magnetic confinement of plasma
Giant Metre wave Radio Telescope (GMRT)Detection of cosmic radio waves
Bose-Einstein condensateTrapping and cooling of atoms by laser beams and magnetic fields

Physics has a great impact on society. In fact, discoveries and developments in physics have changed the face of society. Our life has become more comfortable and luxurious than that of our ancestors.

Some physicists from different countries of the world and their contributions

Name of the scientist/physicistMajor contributions/DiscoveriesCountry of origin
ArchimedesPrinciple of buoyancy, the Principle of the leverGreece
Galileo GalileiLaw of inertiaItaly
Christiaan HuygensWave theory of lightHolland
Isaac NewtonThe universal law of Gravitation, Laws of motion, Reflecting TelescopeU. K.
Michel FaradayLaws of Electromagnetic inductionU. K.
James Clerk MaxwellElectromagnetic theory of LightU. K.
Heinrich Rudolf HertzGeneration of electromagnetic wavesGermany
J. C. BoseUltra-short radio wavesIndia
W. K. RoentgenX-RaysGermany
J. J. ThomsonElectronU. K.
Marie Sklodowska CurieDiscovery of radium and polonium, Studies on natural radioactivityPoland
Albert EinsteinExplanation of photoelectric effect, Theory of relativityGermany
Victor Francis HessCosmic radiationAustria
R.A. MillikanMeasurement of electronic chargeU. S. A.
Ernest RutherfordNuclear model of the atomNew Zealand
Niels BohrQuantum model of the hydrogen atomDenmark
C.V. RamanInelastic scattering of the hydrogen atomIndia
Louis Victor de BroglieWave nature of matterFrance
M.N. SahaThermal IonisationIndia
S.N. BoseQuantum statisticsIndia
Wolfgang PauliExclusion principleAustria
Enrico FermiControlled nuclear fissionItaly
Werner HeisenbergQuantum Mechanics, the Uncertainty principleGermany
Paul DiracRelativistic theory of the electron, Quantum statisticsU. K.
Edwin HubbleExpanding UniverseU. S. A.
Ernest Orlando LawrenceCyclotronU. S. A.
James ChadwickNeutronU. K.
Hideki YukawaTheory of nuclear forcesJapan
Homi Jehangir BhabhaCascade process of cosmic radiationIndia
Lev Davidovich LandauTheory of condensed matter Liquid heliumRussia
S. ChandrasekharChandrasekhar limit, Structure, and evolution of starsIndia
John BardeenTransistors, Theory of superconductivityU. S. A.
C.H. TownesMaser, LaserU. S. A.
Abdus SalamUnification of weak and electromagnetic interactionsPakistan

Fundamental forces in nature

There are four basic forces in nature. These are.

(i) Gravitational force

(ii) Electromagnetic force

(iii) Strong nuclear force

(iv) Weak nuclear force

(i) Gravitational force

  • It is the force of attraction between the two bodies due to their masses.
  • It is always attractive.
  • It is the weakest force in nature.
  • It is a long-range force.
  • This force is governed by Newton’s law of gravitation.”
  • It is also known as the “action-at-a-distance” force.

(ii) Electromagnetic force

  • It is the force of attraction or repulsion between two electric charges.
  • It is both attractive as well as repulsive.
  • It is charge dependent.
  • It is a long-range force.
  • It is 1037 times stronger than the Gravitational force.
  • When the charges are at rest the force between them is called electrostatic force.

(iii) Strong nuclear force

  • Forces operating inside the nuclei are called strong nuclear forces.
  • It is a short-range force (range is ~ 10-15m).
  • It is charge independent.
  • It is an attractive force.
  • It is the strongest force in nature.
  • It is 100 times stronger than the electromagnetic force and 1039 times stronger than the gravitational force.
  • It does not obey the inverse square law.

(iv) Weak nuclear force

  • It is the force existing between the elementary particles emitted during radioactive decay.
  • It appears only in certain nuclear processes such as beta decay.
  • It is not as weak as a gravitational force but much weaker than strong nuclear and Electromagnetic forces.
  • Its range is 10-16m.
NameRelative strengthRangeOperates among
Gravitational force1InfiniteAll objects in the universe
Weak nuclear force1026Very short sub-nuclear size, 10−16𝑚Some elementary particles, particularly electrons and neutrinos
Electromagnetic force1037InfiniteCharged particles
Strong nuclear force1039Short Nuclear size, 10−15𝑚Nucleons, heavier elementary particle

Nature of physical law

The various phenomena occurring in nature are explained based on certain laws. These laws are expressed in terms of some physical quantities. Several physical quantities may change with time, but some physical quantities remain constant in time. The quantities like charge, mass, energy, linear momentum angular momentum, etc. of a system are conserved if no external force acts on the system.

Conserved quantities

The physical quantities that remain constant during a process are called conserved quantities.

Conservation Laws

A law that states the constancy of physical quantity over time within an isolated system is called a conservation law. Ex: Law of conservation of mass. Law of conservation of energy. Law of conservation of charge. Law of conservation of momentum.

Important Questions for preparing for the exam

One mark.

1) What is physics?

2) Name the weakest fundamental force in nature.

3) Who introduced the nuclear model of an atom?

4) Who discovered the neutron?

5) Who won the Nobel Prize in the field of scattering of light by molecules?

6) Who discovered the law of Inertia?

7) Who proposed the electromagnetic wave theory?

8) What is the nature of physical laws?

9) Name the scientist who gave the heliocentric theory?

10) Name the scientist who gave the laws of electromagnetic induction?

11) Who discovered radioactivity?

Two marks.

1) Mention the steps involved in the scientific method.

2) What is reductionism? Give an example.

3) What is unification? Give one example.

4) Mention two physicists who achieved the unification of electricity and magnetism.

5) Name the scientist who achieved the unification of electromagnetism and optics.

6) Mention any two fundamental forces in nature.

7) Name the strongest and weakest fundamental forces in nature.

8) Name the two physicists who discovered an electron and electromagnetic wave.

9) Name two Indian scientists who have been awarded Nobel Prize.

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