2. The word Physics comes from a Greek word physis meaning nature.
Physics is the study of nature and natural phenomena. Physicists try to discover the rules that are operating in nature, on the basis of observations, experiments and analysis.
4. Fundamental Forces in Nature:
In physics I) Gravitational Force II) Electromagnetic Force III) Strong Nuclear Force IV) Weak Nuclear Force are treated as fundamental forces.
I) Gravitational Force:
a) The gravitational force is the mutual force of attraction between any two objects by virtue of their masses. It is a universal force.
b) It plays an important role in the formation and evolution of stars, galaxies and galactic clusters.
II) Electromagnetic Force:
a) For a fixed distance, electromagnetic force between protons is 1036 times the gravitational force between them.
b) Electromagnetic force is the base for the structure of atoms and molecules.
c) Gravity is always attractive, while electromagnetic force may be attractive or repulsive.
III) Strong Nuclear Force:
a) The strong nuclear force binds protons and neutrons in a nucleus.
b) This is strongest of all fundamental forces and about 100 times stronger than electromagnetic force.
c) It is charge independent and acts equally between Proton - Proton, Neutron - Neutron, and Proton -Neutron.
d) Its range is very small (10–15m).
e) It is responsible for the stability of nuclei.
IV) Weak Nuclear Force:
a) This force appears only in certain nuclear processes such as the β - decay.
b) These are weaker than the strong nuclear and electromagnetic forces, but stronger than gravitational forces.
c) Their range is very small (10–16 m).
5. The Raman Effect deals with scattering of light by molecules of a medium when they are excited to vibration energy levels.
6. According to Bose-Einstein statistics a gas of molecule below a certain temperature undergoes a phase transition to a state where a large fraction of atoms populate the same lowest energy state.
7. Conserved Quantities:
In physics any physical phenomenon is governed by certain forces. Several physical quantities will change with time but some special physical quantities will remain constant with time. Such physical quantities are called conserved quantities of nature.
Example: For motion under an external conservation force such as gravitational field the total mechanical energy (i.e. P.E+K.E) is constant or energy is conserved.