CH-1 PHYSICAL
WORLD
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Science means organized knowledge.
It is human nature to observe things and happenings around in the
nature and then to relate them. This knowledge is organized so that it become
well connected and logical. Then it is known as Science. It is a systematic
attempt to understand natural phenomenon and use this knowledge to predict,
modify and control phenomena.
Scientific
Method
Scientific methods are used to observe things and
natural phenomena. It includes several steps :
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Observations
•
Controlled experiments,
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Qualitative and quantitative
reasoning,
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Mathematical modeling,
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Prediction and
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Verification or falsification
of theories.
There is no ‘final’
theory in science and no unquestioned authority in science.
•
Observations and experiments
need theories to support them. Sometimes the existing theory is unable to
explain the new observations, hence either new theories are formed or
modification is done in the existing theories.
•
For example to explain
different phenomena in light, theories are changed. To explain bending of light
a new Wave-theory was formed, and then to explain photoelectric effect help of
quantum mechanics was taken.
Natural Sciences can be
broadly divided in three branches namely Physics, Chemistry and biology
•
Physics is a study of basic laws of
nature and their manifestation in different phenomena.
Principal thrusts in
Physics
•
There are two principal thrusts
in Physics;
•
1.Unification 2. reduction
Unification
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Efforts are made to explain
different phenomena in nature on the basis of one or minimum laws. This is
principle of Unification.
Example: Phenomena of apple falling to ground, moon revolving around
earth and weightlessness in
the rocket, all these phenomena are explained with help of one Law that is, Newtons Law of
Gravitation.
Reductionism
•
To understand or to derive
the properties of a bigger or more complex system the properties of its simpler
constituents are taken into account. This approach is called reductionism.
It is supposed to be the
heart of Physics.
For example a complex thermo dynamical system can be understood by
the properties of its constituent like kinetic energy of molecules and atoms.
The scope of Physics can be
divided in to two domains; Macroscopic
and Microscopic.
•
Macroscopic domain includes
phenomena at the level of Laboratory, terrestrial and astronomical scales.
•
Microscopic domain includes
atomic, molecular and nuclear phenomena.
•
Recently third domain in
between is also thought of with name Mesoscopic Physics. This deals with group
of Hundreds of atoms
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Scope of physics is very wide
and exciting because it deals with objects of size as large as Universe (1025m)
and as small as 10-14 m, the size of a nucleus.
The excitement of Physics is
experienced in many fields Like:
•
Live transmissions through television.
•
Computers with high speed and
memory,
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Use of Robots,
•
Lasers and their applications
Physics in relation to
other branches of Science
Relation to Chemistry.
•
Chemical bonding, atomic number and complex
structure can be explained by physics phenomena of Electrostatic forces,
•
taking help of X-ray diffraction.
Relation to maths - Physical theories make use of various mathematical
concepts which help in the development of theoretical physics.
Relation to Biological Sciences:
·
Physics helps in study of Biology
through its inventions.
·
Optical microscope helps to study
bio-samples, electron microscope helps to study biological cells.
·
X-rays have many applications in
biological sciences.
·
Radio isotopes are used in
cancer.
Physics in relation with Astronomy:
•
Giant astronomical telescope developed
in physics are used for observing planets. Radio telescopes have enabled
astronomers to observe distant limits of universe.
•
Physics related to other
sciences: Laws of Physics are used to study different phenomenas in other
sciences like Biophysics, oceanography, seismology etc.
Fundamental Forces
in Nature
There is a large number of forces experienced or applied. These may
be macroscopic forces like gravitation, friction, contact forces and
microscopic forces like electromagnetic and inter-atomic forces. But all these forces arise from some basic
forces called Fundamental Forces.
Fundamental Forces in Nature..
1. Gravitational force.
•
It is due to Mass of the two
bodies.
•
It is always attractive in
nature.
•
It operates on all objects
of universe.
•
Its range is infinite.
•
It
obeys the inverse square law.
•
Its
field particle is graviton.
•
It
is the weakest force operating in nature.
•
It is a
central and conservative force.
2.Electromagnetic Forces:
•
It’s due to stationery or
moving Electrical charge
•
It may be attractive or
repulsive in nature.
•
It operates on charged
particles
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Its range is infinite.
•
It obeys the inverse square
law.
•
Its field particle is photon.
•
It is also a central as well
as conservative force.
3. Strong nuclear force:
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Operate between Nucleons
•
It may be attractive or
repulsive(It is basically an attractive force).
•
Its range is very short,
within nuclear size (10-15
m).
•
Its strongest force in
nature.
•
It varies inversely with
some higher power of distance.
•
Its field particle is π –
meson.
•
It is a non-central force.
4.Weak Nuclear force:
•
Operate within nucleons i.e.
elementary particles like electron and neutrino.
•
It appears during
radioactive beta decay(The ß– decay is an example of weak force interaction. In
this process, a neutron inside a nucleus changes into a proton by emitting an
electron and an uncharged particle, called antineutrino).
•
Has very short range 10-16m.
•
In a weak interaction, neutrino acts
as the field particle.
Conservation Laws
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In any physical phenomenon
governed by different forces, several quantities do not change with time. These
special quantities are conserved quantities of nature.
Law of conservation of linear momentum: It states that if no external force acts on a
system, the total linear momentum remains conserved. In absence of external
force,
p1 + p2 =
constant
Where p1 and p2 are
linear momenta of the two bodies at any instant.
- It is obtained from Newton’s third law of motion.
- Follows the principle of homogeneity of space i.e.
space possesses same properties at all the points.
Examples:
- When two billiard balls strike, they move in opposite directions.
- The recoil when a bullet is fired from a gun.
- Motion of the rockets.
Law of conservation of energy: It
states that energy can neither be created nor destroyed, but can change its
form from one to another.
- In mechanics, mass is considered fundamental to matter and matter
acquires energy by virtue of its motion or configuration.
- Einstein’s mass-energy equivalent relation is E = m c2.
This has led to law of conservation of mass and energy that
unites both laws of conservation of mass and conservation of energy.
- Release of energy in nuclear fission and fusion is in accordance
with this unified law.
Examples:
- The mechanical energy of a freely falling body remains constant.
(Mechanical energy = Kinetic energy + Potential energy)
- On vibration, the mechanical energy of a simple pendulum remains
constant while it swings between two extreme points.
Law of conservation of angular
momentum : It states that if no external torque acts on a system, the
total angular momentum of the system remains conserved.
- It follows Newton’s third law of rotatory motion. Also, it can be
obtained from principle of isotropy of space e. space
possesses same properties in all directions.
Examples:
- Velocity of a planet orbiting the sun in an elliptical orbit
increases when it is closer to the sun and decreases when it is far from
the sun.
2. A diver jumping from the spring board
exhibits summersaults in air.
The other conservative laws are law of
conservation of charge, spin, lepton number, baryon number, parity etc.
The laws of nature do not change with change of space and time. This
is known as symmetry of space and time. This and some other symmetries play a
central role in modern physics. Conservation laws are connected to this.
Laws
of Physics related to technology :
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Principal of Physics
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Technology
|
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Electromagnetic
Induction
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Electricity Generation
|
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Laws of Thermodynamics
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Steam,
petrol, or diesel Engine
|
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Electromagnetic
Waves propagation
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Radio, TV, Phones
|
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Nuclear chain reaction
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Nuclear reactor for
power
|
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Newtons Second &
Third Law
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Rocket propulsion
|
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Bernoulli’s theorem
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Aero planes
|
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Population inversion
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Lasers
|
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X-rays
|
Medical Diagnosis
|
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Ultra high magnetic
fields
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Superconductors
|
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Digital electronics
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Computers and
calculators
|
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Electromagnetic
Induction
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Electricity Generation
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Physicist
and their contributions
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Name
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Contribution
|
country
|
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Isaac
Newton
|
Law
of Gravitation, Laws of Motion, Reflecting telescope
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U.K.
|
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Galileo
Galilei
|
Law
of Inertia
|
Italy
|
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Archimedes
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Principle
of Buoyancy, Principle of Lever
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Greece
|
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James
Clerk Maxwell
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Electromagnetic
theory, light is an e/m wave.
|
U.K.
|
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W.K.Roentgen
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X-rays
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Germany
|
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Marie
S. Curie
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Discovery
of Radium, Polonium, study of Radioactivity
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Poland
|
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Albert
Einstein
|
Law
of Photo electricity, Theory of Relativity
|
Germany
|
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S.N.Bose
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Quantum
Statistics
|
India
|
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James
Chadwick
|
Neutron
|
U.K.
|
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Niels
Bohr
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Quantum
model of Hydrogen atom
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Denmark
|
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Earnest
Rutherford
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Nuclear
model of Atom
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New
Zealand
|
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C.V.Raman
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Inelastic
Scattering of light by molecules
|
India
|
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Christian
Huygens
|
Wave
theory of Light
|
Holland
|
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Michael
Faraday
|
Laws
of Electromagnetic Induction
|
U.K.
|
|
Edvin
Hubble
|
Expanding
Universe
|
U.S.A.
|
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H.J.Bhabha
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Cascade
process in cosmic radiation
|
India
|
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Abdus
Salam
|
Unification
of week and e/m interactions
|
Pakistan
|
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R.A.Milikan
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Measurement
of Electronic Charge
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U.S.A.
|
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E.O.Lawrence
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Cyclotron
|
U.S.A.
|
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Wolfgong
Pauli
|
Quantum
Exclusion principle
|
Austria
|
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Louis
de Broglie
|
Wave
nature of matter
|
France
|
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J.J.Thomson
|
Electron
|
U.K.
|
|
S.Chandrashekhar
|
Chandrashekhar
limit, structure of stars
|
India
|
|
Christian
Huygens
|
Wave
theory of Light
|
Holland
|
|
Michael
Faraday
|
Laws
of Electromagnetic Induction
|
U.K.
|
|
Edvin
Hubble
|
Expanding
Universe
|
U.S.A.
|
|
Henrick Hertz
|
Electromagnetic Waves
|
Germany
|
|
J.C.Bose
|
Ultra short radio
waves
|
India
|
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Hideki Yukava
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Theory of Nuclear
Forces
|
Japan
|
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W.Heisenberg
|
Quantum mechanics,
Uncertainty principle
|
Germany
|
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M.N.Saha
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Thermal Ionization
|
India
|
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G.N.Ramachandran
|
Triple Helical
structure of proteins
|
india
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