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General Knowledge for Competitive Exams

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Thermal Expansion of Solids, Liquids and Gases

The change in temperature of a body causes expansion or contraction of that body. Most of the substances expand on heating and contract on cooling. This is called thermal expansion. It is interesting to know why the level of mercury rises with temperature, wires attached to electric poles contract or expand with change in season, etc. This all is due to thermal expansion.

Mechanical Properties of Fluids

Some liquids show resistance to motion and it is like internal friction. This is called viscosity. Liquids acquire a free surface when poured in a container. The additional energy that these surfaces have is called surface tension.

Sound: Doppler Effect and Echo

Sound is a form of energy. It is that form of energy which makes us hear. Sound wave is a vibratory disturbance in a medium which carries energy from one point to another without there being a direct contact between the two points. According to Doppler Effect the frequency of sound wave changes with motion, either of the source or of the observer. The reflection of sound wave is called echo. It varies in different mediums.

Refraction of light by Spherical Lenses

Refraction is the change in direction of light when it passes from one medium to another. The working of a lens is based on the refraction of light when they pass through it. Lens is a piece of transparent glass bound by two spherical surfaces and is used to magnify objects. They are of two types convex and concave. The image produced by convex lens is enlarged and the image produced by concave lens is diminished.

Refraction of light through a glass prism

Refraction is the bending of light when it goes from one medium to another so, when a ray of light passes through a glass prism, refraction of light occurs both, when it enters the prism as well as when it leaves the prism. Since the refracting surfaces are not parallel, therefore, the emergent ray and incident ray are not parallel to one another. In this case the ray of light is deviated on passing through the prism.

The Human Eye and its defects

The Human eye works on the refraction of light through a natural convex lens made up of transparent living material and enables us to see things around us. Also, the ability to see is called vision, eyesight or drishti. Sometimes a person cannot able to see distant or nearby objects clearly and have a defect of vision which can be fixed by wearing spectacles.

The Universe: Stars, Sun, Asteroids..in a nutshell

The Universe is everything we can touch, feel, sense, measure or detect. It includes living things, planets, stars, galaxies, dust clouds, light, and even time. All the existing matter and space as a whole is considered as universe. The universe is believed to be at least 10 billion light years in diameter and contains a vast number of galaxies each containing millions or billions of stars.

The Solar System and Satellites

The Solar System consists of the eight planets that orbit our Sun and other celestial bodies such as moons, comets, asteroids, minor planets, and dust and gas. Sun is considered as the centre of the solar system and all the planets revolve around the sun. The eight planets in the solar system in the increasing order of their distance from the Sun are Mercury, Venus, Earth and Mars, Jupiter, Saturn, Uranus and Neptune.

Resistance of a Conductor

Resistance is the hindrance to the flow of electric charge. The obstruction posed in the way of current carrying particles by fixed particles creates resistance in an electric circuit. The measurement of the electric current in an electric circuit therefore, depends on two factors primarily i.e. Potential Difference across the ends of the conductor and Resistance of the conductor. The relationship between current and potential difference is also explained by Ohm’s Law.

Refraction of Light

Refraction of light takes place when light travels from one medium to another. It takes place at the boundary between the two mediums. Also, we know that speed of light is different in different mediums. So, it occurs due to the change in speed of light on going from one medium to another.

Reflection of light from Spherical Mirrors

A spherical mirror is that mirror whose reflecting surface is the part of a hollow sphere of glass. Spherical mirrors are of two types: concave mirrors and convex mirrors. In a concave mirror reflection of light takes place in the bent in surface or concave surface. In a convex mirror the reflection of light takes place at the bulging-out surface or convex surface.

Reflection of Light

Light is a form of energy which enables us to see objects and the straight line along which it travels is called ray of light. Reflection of Light is the process of sending back the light rays which falls on the surface of an object. The image formed due to reflection of an object on a plane mirror is at different places.

Magnetic effects of Electric Current

A current carrying conductor creates a magnetic field around it, which can be comprehended by using magnetic lines of force or magnetic field lines. Magnetic field in a current carrying straight conductor is in the form of concentric circles around it. The direction of magnetic field; in relation to direction of electric current through a straight conductor can be depicted by using the Right Hand Thumb Rule which is also known as Maxwell’s Corkscrew Rule.


A wave is a phenomenon whereby energy is moved without the transference of any material. X-rays, ultraviolet rays, light and radio waves all travel at the same speed through a vacuum.

The Kinetic Theory Of Matter

When a red hot piece of iron cools down, it transfers energy to its surroundings in three possible ways: conduction, convection or radiation.

The Four Fundamental Forces

The interactions between matter can be explained by four forces.

Special And General Theories Of Relativity

Special theory of relativity was formulated by Einstein.


Radioactivity was gradually understood in terms of the disintegration of atomic nuclei. The three types of radiation are alpha decay, beta decay and gamma decay. Alpha radiation occurs when an unstable nucleus breaks down so as to eject a fast-moving nucleus of helium, which consists of two protons and two neutrons.

Nuclear Fission And Fusion

Otto Hahn and Fritz Strassman (1902-80) discovered nuclear fission in 1938. When an isotope of uranium-235 was bombarded with neutrons, it split into two lighter nuclei along with, on average, three neutrons. These neutrons were capable of bombarding and splitting other nuclei, causing more fission to take place.

Motion And Mechanics

Kinematics covers a broad range of topics, from bodies falling to earth, to the description of bodies moving in a straight line, to circular motion.

Introduction to Physics

Physics is the study of the basic laws that govern matter.

Heat and Work

Modern physics sees heat as energy collectively possessed by the particles making up a gas, liquid or solid. A body which possesses energy has the ability to do work.


Electromagnetism is the study of the effects caused by stationary and moving electric charges.

Electric Current

In the late 1790s, Count Alessandro Volta made the first battery. The first practical primary cell (non-rechargeable) was produced by John Frederic Daniell (1790-1845) in 1836, using zinc and copper electrodes. This was followed by the first secondary (rechargeable) cell invented by Gaston Plante (1834-89) in 1859.

Atomic Theories

John Dalton revolutionized science in 1803 when he hypothesized that atoms of different chemical elements, such as hydrogen and oxygen, had different characteristic masses. J.J. Thomson discovered the first subatomic particle -the electron - in 1897.

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