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CHAPTER 1- PHYSICAL WORLD
Definition:
Physics deals with the study of basic laws of nature and their manifestation in
different natural phenomena. Physics deals with the study of matter, energy and how
they interact with each other. It examines the behavior of all kinds of matter from the
smallest of particles to gigantic galaxies. It deals with distance, time scales, temperature
etc.
Science and Scientific Method:
Science is a systematic way of understanding natural phenomena. It is exploring,
experimenting and predicting from what we see around us. Scientific method involves
several steps like i) systematic observations ii) controlled experiments iii) qualitative and
quantitative reasoning iv) mathematical modeling and v) prediction and verification of
theories.
In physics we attempt to explain physical phenomena in terms of few concepts and laws.
The two principal thrusts in physics are
i)
ii)
Unification- it is the attempt to unify the fundamental forces of nature.
Ex- Laws of gravitation, Laws of electromagnetism
Reduction- derives the properties of bigger complex systems from the
properties of its constituent simpler parts.
Ex- Thermodynamics
SCOPE AND EXCITEMENT OF PHYSICS:
There are two domains of interest in physics:
1) Macroscopic domain- Includes phenomena at the laboratory, terrestrial and
astronomical scales.
2) Microscopic domain- Includes phenomena at the atomic, molecular and
nuclear scale.
1) Macroscopic domain- Classical physics deals mainly with macroscopic
phenomena. Classical physics includes the following
MECHANICS
ELECTRODYNAMICS
CLASSICAL PHYSICS
OPTICS
THERMODYNAMICS
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Mechanics- Deals with the study of motion and the effect of forces on bodies.
Electrodynamics- Deals with the phenomena associated with electric and magnetic
fields exhibited by charged bodies
Optics- deals with the phenomena of light and explains working of mirrors, lenses,
microscopes and telescopes.
Thermodynamics- Deals with heat and its relationship with other forms of energy
and work.
2) Quantum physics deals with microscopic phenomena. In quantum physics, mass
and energy are not considered individually but in combination. It considers that
light and other forms of electromagnetic radiation behave both as waves and
particles. Ex- Motion of electrons, proton, neutron and other elementary
particles.
FUNDAMENTAL FORCES IN NATURE:
Issac Newton was the first one to give an exact definition of force in his famous laws
of motion. According to this, force is an external agency applied on a body to change
its state of rest or motion.
There are four fundamental forces in nature:
1) Gravitational force: The force of mutual attraction between any two objects by
virtue of their masses. All objects on the earth, experience the force of gravity
due to the earth. Motion of the moon, artificial satellites around the earth,
motion of planets around the sun, stars, galaxies are all due to gravitational force.
2) Electromagnetic force: It is the force between charged particles. The foce is
attractive for unlike charges and repulsive for like charges. Charges in motion
produce magnetic fields and due to the magnetic field, there is a force on the
moving charge. Since electric and magnetic effects are linked with each other, this
force is called as the electromagnetic force.
3) Strong nuclear force: Strong nuclear force binds protons and neutrons in a
nucleus. It is an attractive force and is the strongest in nature. However it has a
very short range of 10-15m.
4) Weak nuclear force: Weak nuclear force appears only in certain nuclear
processes such as beta decay of a nucleus. The range of weak nuclear force is
extremely small of the order of 10-16m. It is weaker than strong nuclear force.
Among the four forces the strongest force is strong nuclear force and the
weakest force is gravitational force.
NATURE OF PHYSICAL LAWS:
In any physical phenomena governed by different forces, several factors or quantities
change with time. However, some physical quantities remain constant.
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The physical quantities that remain unchanged in a physical process are
called as conserved physical quantities.
The laws that govern the conservation of these quantities are called as
conservation laws.
Conservation law is a statement that some physical quantity remains unchanged
during all possible physical phenomena. The conservation laws have a deep
connection with the symmetries of nature. The conservation laws are stranger than
other laws because anything that happens in nature must not be forbidden by a
conservation law.
Some of the conservation laws commonly used in physics are:
1. Law of conservation of linear momentum in the absence of external forces on a
system of colliding bodies
2. Law of conservation of angular momentum for a rotating body in the absence of
external torque.
3. Law of conservation of total energy during any process.
4. Law of conservation of mass during a chemical process.
5. Conservation of electric charge.
LIST OF IMPORTANT DISCOVERIES:
Some of the important Indian scientists who contributed in the field of
physics were:
1. Raman scattering- CV Raman
2. Structure and evolution of stars- S Chandrashekar
3. Quantum Statistics- Satyendranath Bose
Two physicists who achieved in the unification of electricity and magnetism
were
a) Hans Christian Oersted
b) Michael Faraday
OTHER IMPORTANT DISCOVERIES:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Photoelectric effect, Special theory of relativity- Albert Einstein
Quantum theory of radiation- Max Planck
Electron- JJ Thomson
Neutron- James Chadwick
Principle of buoyancy- Archimedes
Law of inertia, telescope- Galileo Galili
Laws of mechanics, gravitation- Issac Newton
Electromagnetic theory of light- James Clerk Maxwell
X Rays- Wilhelm Roentgen
Electric motor, dynamo, transformer- Michael Faraday
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