By going through these CBSE Class 11 Physics Notes Chapter 1 Physical World, students can recall all the concepts quickly.

## Physical World Notes Class 11 Physics Chapter 1

→ Physics deals with nature and natural phenomenon.

→ Science is the knowledge acquired by man in an organised way.

→ The various steps involved in acquiring knowledge are:

1. systematic observations
2. reasoning
3. model making
4. a theoretical prediction.

→ The theory is the explanation of the behaviour of a physical system using a limited number of laws.

→ A theory is valid if it is able to explain satisfactorily most of the relevant measurements.

→ There is a certain amount of overlapping between Physics, Chemistry and Biology.

→ Advances in Physics are directly related to the advances in experimental observations.

→ A wide diversity in the physical world can be understood on the basis of a few concepts.

It is due to three reasons:
(a) Strict regularities and laws help in quantitative measurements.
(b) There is a small number of common and basic principles covering enormous diversities of scales of the phenomenon.
(c) It is easier to understand a phenomenon by separating important features from unimportant features.

→ The technological development of any society is very closely related to the application of Physics and other branches of science.

→ Measurements are the heart of Physics. In fact, Physics is also defined as the science of measurements.

→ Motion, energy, gravitation, properties of matter in bulk and their atomic origin, study of details of mechanical oscillations and waves, description of matter with a microscope all form a systematic study.

→ Science: An organised attempt of man to know and the knowledge he acquires is science.

→ Physics: It is the subject which deals with nature and natural phenomenon and their quantitative measurements.

→ Scientific method: Scientific method involves systematic observation, reasoning, model making and theoretical prediction altogether.

→ Theory: A scientific theory is the explanation of the natural phenomenon in terms of a limited number of laws.

→ Geocentric theory: It is a theory in which the earth is assumed to be at the centre of the universe.

→ Heliocentric theory: The sun is at the centre of the world consisting of Earth and other planets.

→ Corpuscular theory of light: Newton assumed light to be made up of corpuscles or particles.

→ Hydroelectric energy: Conversion of gravitational energy into ‘ electric energy through water.

→ Thermal power: Conversion of chemical energy of coal by burning it into electric energy.

→ Geothermal energy: It is the heat in the depth of the Earth.

→ Gravitational force: The force is an attraction between two masses is called the gravitational force. This force of attraction between the two bodies is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. The constant of proportionality is called the Gravitational constant or constant of gravitation G.
F = G$$\frac{m_{1} m_{2}}{r^{3}}$$r̂
Its scalar form is F = G$$\frac{m_{1} m_{2}}{r^{2}}$$

→ Constant of gravitation ‘G’: It is equal to the force of attraction acting between two masses each of 1 kg placed 1 m apart in the air.

→ Electromagnetic force: The combined electrostatic and magnetic force between charged particles and magnetic poles is called electromagnetic force.

→ Nuclear or strong forces: The strong attractive forces between particles in a nucleus are called nuclear forces. This force can act within a distance of 10-15m. These forces are charge independent
i. e. even a proton attracts another proton.

→ Weak forces: The forces of interaction between elementary particles are weaker than the strong forces and these activities within a distance of about 10-12 m.