Definition of Physics: The branch of science which deals with study of nature and properties of matter and energy and of interaction between the two groups in traditional fields such as acoustic, optics, mechanics, thermodynamics and electromagnetism as well as in modern extensions including atomic and nuclear physics, cryogenics, solid-state physics, particle physics and plasma physics.

Origin of Physics: The word “physics” comes from Greek knowledge. It is derived from Latin “Physica” from Greek(ta) “Phusika” which means the natural things and in general the field aims to analyse and understand the natural phenomena of universe.

Discussions: When we talk about physics, one thing comes to our mind is the many scientific laws which are statement describing phenomena that have been repeatedly tested and confirmed. Most people hear the word “Physics” and run for cover. But it’s not just for rocket scientist! We are surrounded by physics all the time and whether we realize it or not we use physics everyday.

It explains natural phenomenon in the universe. It is often considered to be the most fundamental science. It provides the basis of all other sciences. Without physics, we could not have biology, chemistry or anything else!

Scope and excitement of Physics
Scope : Physics has a very wide scope. There are three domains of interest which are given as below:

Domain of Physics

Macroscopic Domain	Mesoscopic Domain	Microscopic Domain
The macroscopic domain or scale is the length scale on which objects of processes are of a size that is measurable and observable by the naked eye.	This domain covers between the macroscopic and microscopic domains. It deals with the few tens or hundreds of atoms and several groups of atoms. Now a days, this is an exciting field of research.	This scale is the scale of size or length used to describe objects smaller than those that are easily be seen by naked eye and which required a lens or microscope to see them clearly.

Physics has it’s scope in classical physics and modern physics

Classification of Physics

Classical Physics	Modern Physics
Mechanics  Acoustics  Optics  Thermodynamics  Electromagnetism  Electrostatic  Electro Dynamics  Magnetitics  Special Theory of Relativity	Atomic and Nuclear Physics  Quantum Physics  Relativistic Physics  Solid State Physics  Astro Physics  Biophysics  Chemical Physics  Econophysics  Geophysics  Medical physics  Plasma physics  Low temperature Physics

Classical Physics

1. Mechanics :
 Study of motion of various objects and particles
 Study of force that acts on bodies whether it is at static or in motion
Sub Branches
i.  Static Mechanics : It deals with the force on the bodies at rest.
ii.  Dynamics Mechanics : It deals with the force that affects the bodies in motion.
iii.  Kinematics : It deals with the description and analysis on the cause of force.

2. Acoustics Physics :
 It concerned with the study of the production of sound wave

3. Optics :
 It refers to the study of light
Sub Branches
i.  Physical Optics : It is the study on the production, nature and properties of light
ii.  Physiological Optics : It refers on the part that is played by light with vision
iii.  Geometrical Optics : It deals with the refraction and reflection of light as experienced in the study of mirrors and lenses

4. Thermodynamics :
 It is the study of connection between heat and other form of energies.
 The effects of changes in temperature, pressure and volume on physical system and their relation to energy and work will be covered under thermodynamics.
 The kinetic theory of gases is based upon classical thermodynamics.
 It was also possible to increase efficiency of steam engine by thermodynamics in early days.
 It mention the existence of quantity called entropy.

5. Electromagnetism :
 It deals with the study of the properties of the electric current and magnetism and their relationship.

6. Electrostatics :
 It refers to the electric charges at rest.

7. Electrodynamics :
 It is the study of moving charges.

8. Magnetostatics :
 It is the study of magnetic poles at rest.

9. Special Theory of Relativity :
 It is the study of relationship between electromagnetism and mechanics.

Modern Physics ( Behavior of Matter and Energy Under Extreme Conditions)

1. Atomic physics and nuclear physics :
 It is the study of components ,structure and behavior of the nucleus of an atom

2. Quantum physics :
  It is concerned with the study of the individual nature of the phenomena at the atomic levels.It comprises the atomic and sub-atomic systems and also their interaction with radiation

3. Solid state physics :
 It is the study of all the properties of solid materials. It comprise of things like electrical conduction in crystals of semiconductors and metals ,superconductivity photoconductivity etc.

4. Relativistic physics :
 It is the study of the phenomena that takes place in the frame of reference that is in motion with respect to an observer

5. Astrophysics :
 It is the physics in the universe that deals with the nature of stars and celestial bodies in astronomy

6. Bio-physics :
 It is the study of physical behavior of biological process

7. Chemical physics :
 It is the science of physical relation in the chemistry

8. Econo-physics :
 It deals with the physical process and their relation in the science of economy

9. Geo-physics :
 It is the science of physical relations that happen in our planet

10. Medical physics or Bio -medical physics :
 It is the application,prevention , diagnosis and treatment in the medical field

11. Plasma physics :
 It is the plasma ,fourth state of matter

12. Low temperature physics :
 It is the study of production and maintenance of the temperaturer down to almost absolute zero and the various phenomenon which occur only at that temperature

Excitement :
The excitement of physics comes in conducting new experiments , discovery of the different of the secrets of the nature and the applying the laws of physics for practical purposes

Basic Forces in Nature :

1. Gravitational forces :
 Force of attraction between point masses

2. Electrostatic force :
  Force of attraction or repulsion between point charges at the rest

3. Magnetic force :
 Force of attraction or repulsion between magnets or magnetic substances

4. Electromagnetic force :
 Force between moving charges

5. Nuclear force :
 Strong Force between nucleons

6. Weak force :
 It is not well understood as yet . the range of this force is even less than that of the other

( NOTE: All the above forces will discussed in details in respective chapters of class 11 & 12 )

Conservation laws :

In any physical phenomenon governed by different forces, several quantities may change with time , however some physical quantities remain constant in time . These quantities are conserved quantities in nature . These remarkable facts are the basis of many laws called conservation laws.

1. Law of conservation of linear momentum :
 “ The total linear momentum of the objects , in a given direction , before collision is equal to the total linear momentum of the objects in the same direction after collision if and only if there is no external force acting on a system of colliding objects”

2. Law of conservation of mass-energy :
  “The sum total of mass and energy remains constant in the universe”

3. Law of conservation angular momentum :
 “If there is no external torque acting upon a system , the total angular momentum remains constant”

4. Law of conservation of charges :
 “The total electric charges of an isolated system remains constant”

5. Law of conservation of energy :
 “The total energy of any system remains constant”

( NOTE: There are nearly 14 conservation laws based on symmetry principles in the physics , like law of conservation of baryons , law of conservation of leptons ,law of conservation of isotopic spin , law of conservation of strangeness etc. but they are beyond the syllabus of class 11 & 12 and some conservation laws will be described in details in the coming chapters.)

Physics technology and society :

Technology is the application of various laws, doctrines of physics for practical purpose. Practical application of physics and other branches of science have played very important role in the development of industry and in improving the standard of living of man.

The understanding of electromagnetic waves in the longer wavelength domain has found application in radio, televisions and wireless communication.

Televisions programme from the distant countries ‘live’ via satellites. The satellite communication has resulted in bringing the world to the table top. These satellites also help in forecasting weather and in geophysical survey such as exploration of oil wells. The electricity that we use in our homes and industry is generated at power plant by the conversion of some other form of energies into electrical energy.

Nuclear energy released in fission process is the source of energy in a nuclear reactor which produces electricity.

A host of other applications of the physics have contributed a great deal to the technical advancement of the society. Our society, today is coming more and more science oriented. Thus physics plays a very significant role in technology and our daily lives.