General Science

In 1803, Dalton’s atomic theory considered the atom to be the smallest indivisible constituent of all matter. The Dalton’s theory could explain the law of conservation of mass, law of constant composition and law of multiple proportions known at that time.

Environmental problems arise both due to natural processes and human activities. These problems adversely affect human and other forms of life.

The invention of microscope helped in the discovery of the cells. Robert Hooke discovered the cell in 1665. Soon a cell theory was formulated.

Communicable diseases spread from one person to another by the entry of pathogens (disease causing organisms). Pathogens enter our body through various means, and then multiply there. They can be transferred from one person to another by direct or indirect contact.

Acid rain is caused when nitrogen oxides, SO₂ and particulate matter in the atmosphere react with H₂O to produce acids. Acid rain is harmful to the environment. It affects life in water and on land. The fish cannot survive in acidic water below pH 4.5. It can also damage trees in the forests.

Pollutants like sulphur dioxide which is released while burning sulphur containing fuel and particulate matter like soot present in stagnant air masses, get modified in sunlight and form a sheet called photochemical smog.

Greenhouse is referred to as a chamber where plants are grown in a closed warm environment as compared to the outside temperature. This is normally practised in cold region of the hills. The solar radiations bringing heat (in the form of infra-red rays from the sun) are trapped inside the chamber.

The ozone layer present in the earth's atmosphere prevents the entry of sun's harmful ultraviolet (UV) radiations reaching the Earth's surface. Industrial use of chemicals called chlorofluorocarbons (CFCs) in refrigeration, air conditioning, cleaning solvents, fire extinguishers and aerosols (spray cans of perfumes, insecticides, medicines) damage the ozone layer.

Anything which is unwanted or useless is termed as waste. The waste generated from various sources can be categorized into two types: Biodegradable waste and Non-biodegradable waste.

Any undesirable change in the environment due to human activity is pollution. Each activity, human or industrial, discharges some unwanted substances in the environment. The presence of unwanted substances in a concentration which can have an adverse effect on organisms and environment is called pollution.

Cutting of the natural forest cover is called deforestation. Forests are being cut for various purposes, such as for growing crops and grazing cattle, meeting the demand of wood and paper.

Landslide is often accompanied by cloudburst. A cloudburst is an extreme amount of precipitation, sometimes with hailstorms and thunderstorms. It occurs for few minutes and can create flood conditions which often results in landslides.

In monsoon, massive landslides occur in the hilly regions leading to blockage of roads. A landslide is the gravitational movement of a mass of rock, earth or debris down a slope. It occurs when a hilly slope becomes unstable.

The word Tsunami is a Japanese word meaning ‘Harbor wave’. It involves the displacement of very large quantities of water due to earthquakes, landslides or volcanic eruptions.

From prehistoric times, forests and fire have remained inseparable. The temperate world’s forest ecosystem has been re-generated and rejuvenated with active help of forest fires.

Earthquake is a common phenomenon. It is the shaking, rolling or sudden shock of the earth’s surface. The intensity of earthquake is related to the amount of energy released when rocks give way to the forces within the earth. It is measured with the help of an instrument known as seismograph. The intensity of an earthquake is measured on the Richter scale.

India has a long coastline, which is vulnerable to the tropical cyclones in the Bay of Bengal and the Arabian Sea. The Bay of Bengal region is frequently battered by storms and cyclones.

India being a country of many rivers and with tropical climate is one of the most flood-prone countries of the world. Floods are frequent because most of the rivers are full of water during monsoons.

All living organisms are interdependent, otherwise it would be difficult to live together in a population.

Adaptations are special features that allow a plant or animal to live in a particular place or habitat.

There is a constant need of nutrients by the biotic community for their survival and they take these from the environment. Nutrients in the form of oxygen, carbon dioxide, nitrogen, phosphorus, sulphur or water exists in a definite amount in the environment.

Food provides energy and thus in a food chain, energy is passed from one link to another. This energy flow is unidirectional - the energy which is transferred from one trophic level to the next does not come back.

A simple food chain basically consists of producers, herbivores and carnivores. For example, small fish feeds on phytoplanktons which in turn is being eaten by a bigger fish. This constitutes the food chain.

Biotic community refers to populations of various kinds of organisms living together and sharing the same habitat. An ecosystem houses several biotic communities which interact with each other.

All living and non-living things that occur naturally on the earth constitute the natural environment. All living organisms are dependent on the environment for their survival. Their life is regulated by the environment and in turn they influence the environment.

Carboxylic acids contain the carboxyl (-COOH) functional group. Their general formula is R-COOH. Vinegar which is also called acetic acid has the formula CH₃COOH.

IUPAC name of aldehyde: Suffix al is added by replacing e from the parent alkane.

Alcohols contain the hydroxyl (-OH) functional group. They are named by replacing final e of the parent alkane by -ol. Alcohols are soluble in water because they can form hydrogen bonds with water molecules.

Functional derivatives of hydrocarbons are those compounds which are derived from hydrocarbons by replacing one or more hydrogen atoms with the functional groups.

Unsaturated hydrocarbons contain carbon-carbon double or triple bonds. Unsaturated hydrocarbons having carbon-carbon double bonds (C=C) are called alkenes whereas those having carbon-carbon triple bonds (C≡C) are known as alkynes.

Methane (CH₄) is the simplest alkane in which four hydrogen atoms are linked to the carbon atom in a tetrahedral fashion.

Hydrocarbons are compounds which contain only carbon and hydrogen. The main source of hydrocarbons is petroleum.

The two important oxides of carbon are carbon monoxide (CO) and carbon dioxide (CO₂).

The compounds of carbon can be classified as organic and inorganic compounds.

Carbon occurs in free state (not combined with any other element) in three allotropic forms. Allotropes are different forms of the same element in the same physical state. Earlier only two allotropic forms - graphite and diamond were known. Another allotropic form, fullerene, has been discovered few years back.

Carbon is an important non-metallic element. It is the sixth most abundant element in the universe. It can exist in the free state or in the form of its compounds. It is the major chemical constituent of most organic matter. Carbon is the second most common element in the human body after oxygen. Carbon is present in coal, oil and natural gas.

Carbon is an important non-metallic element. It is the sixth most abundant element in the universe. It can exist in the free state or in the form of its compounds. It is the major chemical constituent of most organic matter. Carbon is the second most common element in the human body after oxygen. Carbon is present in coal, oil and natural gas.

Metals and non-metals are put to many uses which are based upon their properties.

Non-metals are electronegative in nature. They generally have 5, 6 or 7 electrons in their valence shells. They have tendency to form anion by gaining electrons.

The earth crust is the major source of metals. Some metal salts are also present in sea. The constituents of earth crust which contain these metals or their compounds are known as minerals.

More reactive metals displace less reactive metals from their compounds in aqueous solutions.

Metals react with air and form their oxides. This oxide formation tendency of metals affects their physical and chemical properties. For example, a green layer over old copper coin is due to oxidation leading to formation of copper oxide which is finally converted to basic copper carbonate on its surface due to its oxidation.

Metals are electropositive in nature. They generally have 1, 2 or 3 electrons in their valence shells and readily lose these electrons to form positively charged ions (cations).

Elements can be broadly divided into two categories: metals and non-metals. They differ both in physical and chemical properties.

Satellites are bodies that revolve around planets. All the planets in Solar System, except Mercury, have natural satellites. Moon is a natural satellite of the Earth. But we have artificial satellites launched by several countries.

Invention of the telephone is credited to Alexander Graham Bell. The telephones are of several types: hand sets, mobile phone, satellite phone and through internet. The basic function of a phone is to allow communication of voice both ways.

RADAR is an acronym for Radio Detection And Ranging and is useful in many ways.

SONAR is a technique that makes use of the property of sound. SONAR stands for SOund NAvigation and Ranging. This works on the principle of echo of transmitted sound waves from objects. For instance, if you hit a wall in front with a tennis ball, the ball will bounce back to you. But if the wall is removed, the ball will not come back to you.

Sound level is measured in units of decibel (dB). Here deci means one-tenth and bel is the level of sound. The term Bel is after the name of inventor of telephone, Alexander Graham Bel.

The waves can be of different types. These may be mechanical or electromagnetic. Mechanical wave is a term used for those waves that require a medium for travelling. Its speed is dependent on the properties of the medium such as inertial and elastic properties.