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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.

Vertical division of power among different levels of government is one of the major forms of power-sharing in modern democracies. It is most commonly referred to as federalism.

Thermodynamics is concerned with the relationship between other forms of energy and heat. It explains how thermal energy is converted from other forms of energy. The energy coming from heat is termed thermal energy. When the tiny particles within an object move, they generate heat, more amount of heat is generated, when these particles move at a faster pace.

In a democracy, all power does not rest with any one organ of the government. An intelligent sharing of power among legislature, executive and judiciary is very important to the design of a democracy.

We face a dilemma: democracy is seen to be good in principle, but felt to be not so good in its practice. This dilemma invites us to think hard about the outcomes of democracy.

A political party is a group of people who come together to contest elections and hold power in the government. They agree on some policies and programmes for the society with a view to promote the collective good. Parties reflect fundamental political divisions in a society.

The existence of social diversity does not threaten democracy. Political expression of social differences is possible and sometimes quite desirable in a democratic system. Three kinds of social differences that can take the form of social divisions and inequalities are social differences based on gender, religion and caste.

Democracy is a form of government in which the rulers are elected by the people. In a democracy the final decision-making power must rest with those elected by the people.

Rights are reasonable claims of persons recognised by society and sanctioned by law. Rights are necessary for the very sustenance of a democracy.

President is the head of the state and is the highest formal authority in the country. Prime Minister is the head of the government and actually exercises all governmental powers. He takes most of the decisions in the Cabinet meetings.

Elections take place regularly in any democracy. Elections is a mechanism by which people can choose their representatives at regular intervals and change them if they wish to do so.

The constitution of a country is a set of written rules that are accepted by all people living together in a country. Constitution is the supreme law that determines the relationship among people living in a territory (called citizens) and also the relationship between the people and government.

Three-fourth of the earth's surface is covered with water, but only a small proportion of it accounts for freshwater that can be put to use. This freshwater is mainly obtained from surface run off and ground water that is continually being renewed and recharged through the hydrological cycle.

Biodiversity or Biological Diversity is immensely rich in wildlife and cultivated species, diverse in form and function but closely integrated in a system through multiple network of interdependencies.

We use different materials and services in our daily life. Some of these are available in our immediate surroundings, while other requirements are met by bringing things from other places.

Production of goods in large quantities after processing from raw materials to more valuable products is called manufacturing.

We use different things in our daily life made from metal. Various metals are extracted from minerals after proper refinement. Minerals are an indispensable part of our lives.

1. In which hemisphere does India lie?

Northern hemisphere.

1. Why are people considered an important part of society?

People are considered an important part of society as they develop the economy and the society, make and use resources. People are both producers and consumers of the resources.

1. What is climate?

Climate refers to sum total of weather conditions over a large area for a long period of time (30 - 40 years).

1. What is a river/drainage basin?

A river/drainage basin is an area drained by a single river system.