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Atoms are the building blocks of elements. They are the smallest parts of an element that chemically react. The first atomic theory, proposed by John Dalton in 1808, regarded atom as the ultimate indivisible particle of matter.

Current through a given area of a conductor is the net charge passing per unit time through the area.

Electrostatic force is a conservative force. Work done by an external force (equal and opposite to the electrostatic force) in bringing a charge q from a point R to a point P is q(V_P - V_R), which is the difference in potential energy of charge q between the final and initial points.

Electric and magnetic forces determine the properties of atoms, molecules and bulk matter.

From simple experiments on frictional electricity, one can infer that there are two types of charges in nature; and that like charges repel and unlike charges attract. By convention, the charge on a glass rod rubbed with silk is positive; that on a plastic rod rubbed with fur is then negative.

Semiconductors are the basic materials used in the present solid state electronic devices like diode, transistor, ICs, etc.

Lattice structure and the atomic structure of constituent elements decide whether a particular material will be insulator, metal or semiconductor.

Environmental problems may arise due to natural disasters or due to human activities.

India is a large country. India is the seventh largest country of the world. It extends from the state of Jammu and Kashmir in the North to the state of Tamil Nadu in the South; from the state of Arunachal Pradesh in the east to the state of Gujarat in the west.

India has monsoon type of climate. The word monsoon refers to the seasonal reversal of the wind direction in a year. Due to this, India has four prominent seasons - cold weather season, hot weather season, advancing southwest monsoon season and post or retreating monsoon season.

Alkyl or Aryl halides may be classified as mono, di, or polyhalogen (tri-, tetra-, etc.) compounds depending on whether they contain one, two or more halogen atoms in their structures.

The chemistry of coordination compounds is an important and challenging area of modern inorganic chemistry. During the last fifty years, advances in this area, have provided development of new concepts and models of bonding and molecular structure, novel breakthroughs in chemical industry and vital insights into the functioning of critical components of biological systems.

The d-block consisting of Groups 3-12 occupies the large middle section of the periodic table. In these elements the inner d orbitals are progressively filled. The f-block is placed outside at the bottom of the periodic table and in the elements of this block, 4f and 5f orbitals are progressively filled.

Chemical kinetics is the study of chemical reactions with respect to reaction rates, effect of various variables, rearrangement of atoms and formation of intermediates.

Chemistry, as we understand it today is not a very old discipline. People in ancient India, already had the knowledge of many scientific phenomenon much before the advent of modern science. They applied the knowledge in various walks of life.

Hydrocarbons are the compounds of carbon and hydrogen only. Hydrocarbons are mainly obtained from coal and petroleum, which are the major sources of energy.

Organic compounds are formed due to covalent bonding. The nature of the covalent bonding in organic compounds can be described in terms of orbitals hybridisation concept, according to which carbon can have sp³, sp² and sp hybridised orbitals.

Redox reactions form an important class of reactions in which oxidation and reduction occur simultaneously.

When the number of molecules leaving the liquid to vapour equals the number of molecules returning to the liquid from vapour, equilibrium is said to be attained and is dynamic in nature.

Thermodynamics deals with energy changes in chemical or physical processes and enables us to study these changes quantitatively and to make useful predictions. For these purposes, we divide the universe into the system and the surroundings.

Kössel’s first insight into the mechanism of formation of electropositive and electronegative ions related the process to the attainment of noble gas configurations by the respective ions. Electrostatic attraction between ions is the cause for their stability. This gives the concept of electrovalency.

An atom has a nucleus. The nucleus is positively charged. The radius of the nucleus is smaller than the radius of an atom by a factor of 10⁴. More than 99.9% mass of the atom is concentrated in the nucleus.

Atom, as a whole, is electrically neutral and therefore contains equal amount of positive and negative charges.

In Thomson’s model, an atom is a spherical cloud of positive charges with electrons embedded in it.

The minimum energy needed by an electron to come out from a metal surface is called the work function of the metal. Energy (greater than the work function (φ_ο) required for electron emission from the metal surface can be supplied by suitably heating or applying strong electric field or irradiating it by light of suitable frequency.

Huygens’ principle tells us that each point on a wavefront is a source of secondary waves, which add up to give the wavefront at a later time.

Reflection is governed by the equation ∠i = ∠r′ and refraction by the Snell’s law, sini/sinr = n, where the incident ray, reflected ray, refracted ray and normal lie in the same plane.

Maxwell found an inconsistency in the Ampere’s law and suggested the existence of an additional current, called displacement current, to remove this inconsistency. This displacement current is due to time-varying electric field.

An alternating voltage v = v_m sin ωt applied to a resistor R drives a current i = i_m sin ωt in the resistor, i_m = v_m/R. The current is in phase with the applied voltage.

The magnetic flux through a surface of area A placed in a uniform magnetic field B is defined as, Φ_B = B.A = BA cos θ where θ is the angle between B and A.

The science of magnetism is old. It has been known since ancient times that magnetic materials tend to point in the north-south direction; like magnetic poles repel and unlike ones attract; and cutting a bar magnet in two leads to two smaller magnets. Magnetic poles cannot be isolated.

The total force on a charge q moving with velocity v in the presence of magnetic and electric fields B and E, respectively is called the Lorentz force.

The property of an object by virtue of which it cannot change its state of uniform motion along a straight line or rest on its own is called as inertia. It is the measure of the mass of a body.

Motion in a plane is the motion in two dimensions, for instance, projectile motion, circular motion and so on.

A body is said to be in motion if it changes its position with respect to time.

Some of the common systems of units that are used in physics are: CGS system, FPS system, MKS system, and SI system.

There are four types of waves - mechanical, transverse, longitudinal, progressive.

Oscillation is a measure of some repetitive variation, as a function of time. It can be measured with respect to a state of equilibrium. The most common and simplest example for oscillation is the motion of a simple pendulum.

The kinetic theory of gases explains the behavior of molecules, which should further explain the behavior of an ideal gas. Ideal Gas equation consists of the pressure (P), volume (V), and temperature (T) of gases at low temperature and the equation is: PV = nRT.

By definition, matter or material is anything that has mass and occupies space. Everything we see around us is matter. For example, a water bottle is made up of plastic or any metal, both of which are examples of matter.

Fluids are the substances which move or flow in a certain direction when an external force is applied to them. Fluids can be either gases or liquids. However, when you study fluids and their mechanical properties, you come across two topics namely hydrodynamics and hydrostatics.

What happens to a rubber band when you stretch it and let go? It deforms but regains its original nature when you stop applying a force. But say, you take an aluminium rod and try to bend it using your arm strength. You somehow do manage to bend it a little and then stop applying force. Does the rod regain its original shape? Of course not.

Gravitation or gravity is a naturally occurring phenomenon or a force which exists among all material objects in the universe.

Imagine a rectangular block placed on the slanting edge of a right-angled triangle. If the block is assumed to slide down this edge without any side movement, every point in the rectangular block experiences the same displacement and more importantly, the distance between the points is also maintained.

Work is the measurement of energy transfer that takes place when an object is displaced by an external force applied in the direction of the displacement.

Different persons can have different developmental goals. What may be development for one may not be development for the other. It may even be destructive for the other.

Globalisation is the process of rapid integration of countries. This is happening through greater foreign trade and foreign investment. MNCs are playing a major role in the globalisation process.

In a barter system where goods are directly exchanged without the use of money, double coincidence of wants is an essential feature. In contrast, in an economy where money is in use, money by providing the crucial intermediate step eliminates the need for double coincidence of wants.

When we produce a good by exploiting natural resources, it is an activity of the primary sector. Since most of the natural products we get are from agriculture, dairy, fishing, forestry, this sector is also called agriculture and related sector.

Inputs like education and health helped in making people an asset for the economy. Investment in human capital (through education, training, medical care) yields a return just like investment in physical capital.

Food security of a nation is ensured if all of its citizens have enough nutritious food available, all persons have the capacity to buy food of acceptable quality and there is no barrier on access to food.

Poverty has many dimensions. Normally, this is measured through the concept of poverty line. A common method used to measure poverty is based on the income or consumption levels. Through this concept we analysed main global and national trends in poverty.

Farming is the main production activity in the village. Over the years there have been many important changes in the way farming is practiced. These have allowed the farmers to produce more crops from the same amount of land.