Physical World – Class 11th

Scope Of Physics

Scope of Physics is vast as it covers quantities with length magnitude as high as 10 4m or more and as low as 10-14 m or less. Based on the scope of physics it is divided into 2 types

1.  Macroscopic Domain &
2. Microscopic Domain

1. Macroscopic Domain:

   The macroscopic domain includes phenomena at large scales like a laboratory, terrestrial and astronomical. It includes the following subjects:

   • • Mechanics:

       It is based on Newton’s laws on motion and the laws of gravitation. It is concerned with the motion/equilibrium of particles, rigid and deformable bodies and general system of particles.
       Examples:
       a. Propulsion of rocket by ejecting gases
       b. Water/Sound waves

     • Electrodynamics:

       It deals with electric and magnetic phenomena associated with charged and magnetic bodies.
       Examples:
       a. motion of a current-carrying conductor in a magnetic field
       b. the response of a circuit to an ac voltage (signal)

     • Optics:

       It deals with phenomena involving light.
       Examples:
       a. Reflection and refraction of light
       b. Dispersion of light through a prism

     • Thermodynamics:

       It deals with systems in macroscopic equilibrium and changes in internal energy, temperature, entropy, etc. of systems under the application of external force or heat.
       Examples:
       a. Efficiency of heat engines.
       b. Direction of physical and chemical processes.

2. Microscopic Domain:

   Microscopic Domain includes and deals with phenomena like atomic, nuclear & molecular subjects.

Factors responsible for the progress of Physics:

• Quantitative analysis along with qualitative analysis.
• Application of universal laws in different contexts.
• Approximation approach (complex phenomena broke down into a collection of basic laws).
• Extracting and focusing on the essential features of a phenomenon.

Hypothesis, Axiom, and Models

The hypothesis is a supposition without assuming that it is true. It may not be proved but can be verified through a series of experiments.

• Axiom is a self-evident truth that it is accepted without controversy or question.
• Model is a theory proposed to explain observed phenomena.
• Assumption is the basis of physics, where a number of phenomena can be explained. These assumptions are made from experiments, observation and a lot of statistical data.

Technological applications of Physics

Several examples where Physics and its concepts have led to discoveries/inventions are listed below.

• The steam engine was developed from the industrial revolution in the eighteenth century.
• Wireless communication was developed after the discovery of laws of electricity and magnetism.
• Neuron-induced fission of uranium, done by Hahn and Meitner in 1938, led to the formation of nuclear power reactors and nuclear weapons.
• Conversion of solar, wind, geothermal etc.energy into electricity.

Fundamental Forces in Nature or Laws of Nature

The forces which we see in our day to day life like muscular, friction, forces due to compression and elongation of springs and strings, fluid and gas pressure, electric, magnetic, interatomic and intermolecular forces are derived forces as their originations are due to a few fundamental forces in nature.

The Fundamental laws are

1. Gravitational Force: It is the force of mutual attraction between any two objects by virtue of their masses. It is a universal force as every object experiences this force due to every other object in the universe.
2. Electromagnetic Force: It is the force between charged particles. Charges at rest have electric attraction (between unlike charges) and repulsion (between like charges). Charges in motion produce magnetic force. Together they are called Electromagnetic Force.
3. Strong Nuclear Force: It is the attractive force between protons and neutrons in a nucleus. It is charge-independent and acts equally between a proton and a proton, a neutron and a neutron, and a proton and a neutron. Recent discoveries show that protons and neutrons are built of elementary particles, quarks.
4. Weak Nuclear Force: This force appears only in certain nuclear processes such as the β-decay of a nucleus. In β-decay, the nucleus emits an electron and an uncharged particle called neutrino. This particle was first predicted by Wolfgang Pauli in 1931.

The below table shows the difference between the above forces:

Unification of Forces

There have been physicists who have tried to combine a few of the above fundamental forces. These are listed in the table below:

Conserved Quantities

• Physics gives laws to summarize the investigations and observations of the phenomena occurring in the universe.
  Physical quantities that remain constant with time are called conserved quantities.
  Example: for a body under external force, the kinetic and potential energy change over time but the total mechanical energy (kinetic + potential) remains constant.
• Conserved quantities can be a scalar (Energy) or vector (Total linear momentum and total angular momentum).

Conservation Laws

A conservation law is a hypothesis based on observation and experiments which cannot be proved. These can be verified via experiments.

Law of conservation of Energy:

• According to the general Law of conservation of energy, the energies remain constant over time and convert from one form to another.
• The law of conservation of energy applies to the whole universe and it is believed that the total energy of the universe remains unchanged.
• Under identical conditions, nature produces symmetric results at different time.

Law of conservation of Mass

This is a principle used in the analysis of chemical reactions.

• A chemical reaction is basically a rearrangement of atoms among different molecules.
• If the total binding energy of the reacting molecules is less than the total binding energy of the product molecules, the difference appears as heat and the reaction is exothermic.
• The opposite is true for energy-absorbing (endothermic) reactions.
• Since the atoms are merely rearranged but not destroyed, the total mass of the reactants is the same as the total mass of the products in a chemical reaction.
• Mass is related to energy through Einstein theory, E = mc2, c – the speed of light in vacuum

Law of conservation of linear momentum

• The symmetry of laws of nature with respect to translation in space is termed as the law of conservation of linear momentum.
• Example law of gravitation is the same on earth and moon even if the acceleration due to gravity at the moon is 1/6th than that at earth.

Law of conservation of angular momentum

Isotropy of space (no intrinsically preferred direction in space) underlies the law of conservation of angular momentum.