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Continents and Oceans

The Earth – Shape and Size

Shape of the Earth

Pythagoras (572-500 B.C.), a Greek philosopher and mathematician, was among the first to suggest that the Earth was shaped like a globe.

The Earth is not flat

1.    If the Earth were a flat disc, then the rising Sun would have been seen at all places at the same time. But this does not happen. Places in the east see the rising Sun earlier.

2.    When a ship approaches land, its funnel or mast is seen first and then the hull. If the Earth had been flat, the whole ship would have been seen at the same time.


The Earth is a sphere

1.    The Earth is rarely oriented in the same position during successive eclipses but it always casts a circular shadow, thus proving that the Earth is a sphere. A sphere is the only solid body that will always cast a circular shadow.

2.    At the North Pole, the Pole Star can always be observed at 90 degrees in the sky, since the star lies in the line with the axis of the Earth.

3.    As one travels southwards, the angle of Pole Star decreases.

4.    At the Equator the angle becomes zero degree.

5.    This observation proves that the path of travel is an arc of a circle.

6.    The Sun, Moon and all the heavenly bodies appear to be spherical when viewed from different positions. It seems logical to conclude that the Earth is no exception.

7.    The photographs of the Earth taken from the space prove beyond any doubt that the Earth is a sphere.


The Earth as an Oblate Spheroid

1.    Refined measurements of the Earth have proved that the true form of the Earth resembles a sphere that has been compressed at the poles and made to bulge at the Equator. This form is known as an oblate spheroid.

2.    The various factors which make the earth suitable for

3.    life to evolve and survive are

4.    The earth has all the essential elements like carbon (in the form of C02), hydrogen (H2), nitrogen (N2) and oxygen (02) which act as building blocks for the origin of life.

5.    The earth is neither too hot nor too cold. It has the right temperature range for carrying out the life-sustaining chemical reactions.

6.    The earth has a lot of water in the form of lakes, rivers and oceans for the growth and survival of life.

7.    The earth has enough oxygen gas in its atmosphere for the survival of living beings through breathing.

8.    The earth has a protective blanket of ozone layer high up in its atmosphere to save life from harmful ultraviolet radiations coming from the sun.


Oceania

Australia with New Zealand, Tasmania, New Guinea and the Pacific Islands (Micronesian, Melanesian and Polynesian Islands) is called Australasia by some geographers while some others call it “Oceania”, which includes proximate islands (Caribbean countries etc.).


Oceans on The Earth

There are four oceans. In order of their size, they are : Pacific Ocean, Atlantic Ocean, Indian Ocean and Arctic Ocean.


Pacific Ocean

1.    The explorer Ferdinand Magellan, who circumnavigated the Earth, named the ocean “Pacific” meaning calm or peaceful.

2.    The Pacific Ocean (Area : 166,240,000 sq. km.) is the largest ocean of the world.

3.    It is the deepest ocean with an average depth of 4,200 m.

4.    The Mariana Trench is the world’s deepest trench with a depth of 11,033 metres (36,201 feet).

5.    Most of the islands of this ocean are of volcanic or coral origin.


Atlantic Ocean

1.    The Atlantic Ocean (Area : 86,560,000 sq. km.) is the second largest ocean in the world

2.    Its name is derived from Atlas, a Titan (giant) in Greek mythology.

3.    The Atlantic Ocean has the longest coastline.

4.    The Atlantic Ocean is the busiest ocean for trade and commerce since its shipping routes connect the two most industrialized regions, namely Western Europe and N.E. United States of America.

5.    The Atlantic Ocean was formed millions of years ago when a rift opened up in the Gondwanaland and the continents of South America and Africa separated. The separation continues even today and the Atlantic Ocean is still widening.

6.    The continental islands of Newfoundland and British Isles are the major ones.

7.    Volcanic islands are fewer and they include those of Cuba, Jamaica and Puerto Rico. Iceland is the largest island of volcanic origin.


Indian Ocean

1.    The Indian Ocean (Area : 73,430,000 sq. km.) is the only ocean named after a country.

2.    The Indian Ocean is deeper than the Atlantic Ocean.

3.    It contains numerous continental islands, Madagascar and Sri Lanka are being the largest ones.

4.    Some of the islands of volcanic origin are those of Mauritius, Andaman and Nicobar, Seychelles, Maldives and Lakshadweep are of coral origin.


South Indian Ocean

1.    Warm currents : 1. South Equatorial 2. Mozambique 3. Madagascar 4. Agulhas.

2.    Cool Currents : 1. Antarctic drift 2. West Australian currents.


Arctic Ocean

1.    The Arctic Ocean (Area : 13,230,000 sq. km.) is the smallest of all the oceans.

2.    It lies within the Arctic Circle, hence the name Arctic Ocean.

3.    The North Pole lies in the middle of the Arctic Ocean.

4.    Most of the parts of Arctic Ocean remains frozen with thick ice for most of the days every year.

5.    It is the shallowest of all oceans, with an average depth of 1,500 m.

6.    It has the least salinity of all the oceans. It has a salinity of 20 unit per thousand.


Ocean Currents

1.    The flow of a large amount of water in a definite direction with a great intensity is known as Ocean Current.

2.    Ocean Currents are of two types-Hot and Cold.


Hot Currents

1.    The currents flowing from tropical zones of lower latitudes to higher temperate and sub polar zones are known as hot water currents.


Cold Currents

1.    The currents flowing from higher latitudes to lower latitudes are known as cold water currents.
2.    The only exception to the conduction of ocean currents is found in the Indian Ocean. The flow of currents changes here with a change in the direction of the Monsoon Winds. The hot currents flow towards cooler oceans and the cold currents flow towards the warmer oceans.

 

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Notes on Salient Features of Indian Constitution


The Constitution of India is the longest, written constitution in the world, with 464 articles under 25 parts, 12 schedules, 5 appendices, and 122 amendments today. The Constitution of India is the lengthiest constitution in the world as no other constitution contains as many articles.

India is a Sovereign, Socialist, Secular, Democratic and Republic State

The Constitution declares India to be a Sovereign, Socialist, Secular, Democratic, Republic.

➤Sovereign means absolutely independent, it is not under the control of any other state.

➤Socialist involves a system which will endeavour to avoid concentration of wealth in a few hands and will assure its equitable distribution. It also implies that India is against exploitation in all forms and believes in economic justice to all its citizens.

➤Secular means there is no state religion in India. Every citizen is free to follow and practice the religion of his/her own choice. The state cannot discriminate among its citizens on the basis of religion.

➤Democratic means that the power of the government is vested in the hands of the people, people exercise this power through their elected representatives who are responsible to them. All citizens enjoy equal political rights.

➤Republic means that the head of the state is not a hereditary monarch.

➤Federal Government: The constitution provides for a federal form of government. In a federation, there are two governments- at the central level and at the state level. The powers of the government are divided between the central government and the state government.

➤Fundamental Rights & Fundamental Duties: Fundamental Rights and Fundamental Duties are the most important characteristics of the Constitution. Fundamental Rights are considered to be essential for the proper moral and material uplift of people. These rights are fundamental in the sense that any law passed by the legislature in the country would be declared as null and void if it is derogatory to the rights guaranteed by the constitution.

➤Parliamentary Government: Indian Constitution provides a parliamentary form of government. President is the nominal head of the state. The government is run by the Prime Minister and other members of the Council of Minister. The Council of Ministers is collectively responsible to the Parliament.

➤Partly rigid and partly flexible: The Constitution of India is neither wholly rigid nor wholly flexible. It is partly rigid and partly flexible.

• Certain provisions of the constitution can be amended by a simple majority in the Parliament.

• Certain provisions can be amended by a two-thirds majority of the Parliament and its ratification by at least fifty percent of states.

• The remaining provisions can be amended by the Parliament by the two-thirds majority.

➤Single Citizenship: In the federation, normally we have double citizenship. In the U.S.A every citizen of the United States of America is also a citizen of the state in which he or she resides. But the constitution of India provides single citizenship to every Indian.

➤Independent Judiciary: The Indian Constitution provides for an independent judiciary. The judiciary has been made independent of the Executive as well as the Legislature. The judges give impartial justice

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List Of Diseases Caused By Virus, Bacteria, Protozoa And Worm


Disease caused by Viruses:

Chicken pox – It is caused by Varicella-zoster virus.

Small Pox – It is caused by Variola virus.

Common Cold -It is caused by Rhinovirus.

AIDS (Acquired Immunono Deficiency Syndrome) – It is caused by Human Immunodeficiency Virus (HIV).

Measles -It is caused by Measles virus.

Mumps -It is caused by Mumps virus.

Rabies – It is caused by Rabies virus (Rhabdoviridae family).

Dengue fever -It is caused by Dengue virus.

Viral encephalitis – It is an inflammation of the brain. It is caused by rabies virus, Herpes simplex, polio virus, measles virus, and JC virus.

Disease caused by Bacteria:

Whooping Cough – It is caused by a bacterium called Borde tella pertussis.

Diphtheria – It is caused by Coryne bacterium diphtheriae.

Cholera – It is caused by Vibrio cholerae.

Leprosy – It is caused by Mycobacterium leprae.

Pneumonia- It is caused by Streptococcus pneumoniae.

Tetanus – It is caused by Clostridium tetani.

Typhoid – It is caused by Salmonella typhi.

Tuberculosis – It is caused by Mycobacterium tuberculosis.

Plague – It is caused by Yersinia pestis.

Disease Caused by Protozoans: 

Malaria It is spread by Anopheles mosquitoes. The Plasmodium parasite that causes malaria is neither a virus nor a bacteria

Amoebic dysentery: It is caused by Entamoebahistolytica.

Sleeping sickness: It is caused by Trypanosomabrucei.

Kala azar It is caused by Leishmaniadonovani.

Disease Caused by Worms

Tapeworm: They are intestinal parasites. It cannot live on its own. It survives within the intestine of an animal including human.

Filariasis: It is caused by thread.

Pinworm: It is caused by small, thin, white roundworm called Enterobiusvermicularis

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Notes on Atomic models and Quantum numbers



➤Atomic Models:

To show the arrangement of fundamental particles in an atom various models were proposed, some important models are as follows:

➤Dalton’s Atomic Theory:

The different assumptions of this theory are as follows;

• All matters are made up of atoms which are indivisible and indestructible.

• All the atoms of a given element have identical properties including identical mass.

• Atoms combine in small whole numbers to form the compound.

• Chemical reactions involve only combination, separation or rearrangement of atoms.

➤Thomson’s Atomic Model:

• Every atom consists of uniformly positively charge sphere having the radius in the order of 10-10 m  in which entire mass is uniformly distributed and negatively charges electrons are embedded randomly.

• Thomson uses the cathode ray tube to gives its atomic model.

• This model is known as the plum pudding model.

• According to him, negative charge particles are distributed in the atom and to balance this negative charge some positive charge particles also present in it.

• The atom as a whole is neutral.

➤Drawbacks of Thomson’s Atomic Model:

• It could not explain the origin of spectral series of hydrogen and other atoms.

• It could not explain large-angle scattering of alpha particles.

➤Rutherford’s Atomic Model:

• He fired a beam of the alpha particle on a sheet of gold to gives its model theory.

• The existence of nucleus was proved by Rutherford in his alpha particle scattering experiment.

• The entire positive charge and almost entire mass of the atom is concentrated at its centre in a very tiny region of the order of 10-15m, called the nucleus.

• The negatively charged electrons revolve around the nucleus in different orbits.

• The total positive charge on the nucleus is equal to the total negative charge on electron; therefore atom as overall is neutral.

• A nucleus consists of positively charged protons and electrically neutral neutrons.

➤Limitations of Rutherford’s Atomic models:

• According to Maxwell electromagnetic wave theory, an accelerated charged particle emits its energy in the form of electromagnetic waves. Therefore an electron must emit emits energy during its course of accelerated motion around the nucleus. Due to which the radius of its path will decrease gradually and ultimately it will fall in the nucleus.

➤Plank’s Quantum Theory:

 Planck gave a new revolutionary theory of radiation known as the quantum theory of radiation.

According to this theory

Radiant energy is not emitted or absorbed continuously but discontinuously in the form of small packets of energy known as photons (quanta).

The amount of energy associated with a quantum of radiation is proportional to the frequency of radiation.

Energy = hν

Where h is Planck’s constant

➤Bohr’s Model:

• Bohr’s model is based on the quantum physics i.e. quantization of energy

• This model is similar to the planetary model in which electron revolves around the nucleus in the specific orbit

• Bohr’s model is considered as the primitive hydrogen atom model

• Every orbit has a specific size and energy level.

• Smallest energy is found in the smallest orbit as energy is related to the size of the orbit.

• Electrons can move from one orbit to another by emitting or absorbing energies according to quantum mechanisms.

➤Heisenberg’s Uncertainty Principle:

• According to this theory, the position and velocity or momentum cannot be measured at a single instant.

• Heisenberg principle is not applicable to macroscopic objects

➤De-Broglie Concept:

• De Broglie states that electron has dual nature i.e. wave nature and particle nature

• Wavelength (l) of an electron is inversely proportional to its momentum (p)

        l=h/p=h/mv, where h is Planck’s constant

➤Shell:

The electron has a definite energy characteristic of the orbit in which it is moving. These orbit or energy levels or shells therefore also known as stationary orbits.

n=1,2,3,4

Shell =K,L,M,N

The shell with n=1 is closest to the nucleus and an electron in this level has the lowest energy as it is closest to the positive charge of the nucleus.

➤Distribution of electrons in different orbits:

• It was suggested by Bohr and Burry and the rules that govern it are as follows:

• The maximum number of electrons present in a shell is given by the formula 2n2 where n=1,2,3 and 4 for K, L, M and N shells respectively.

• The maximum number of electrons that can be accommodated in the outermost orbit is 8.

• The shells are filled in a step-wise manner.

➤Electronic Configuration:

• It is the arrangement of electrons in various shells, subshells and orbitals in an atom.

• It is written as 2,8,8,18,32  

• The maximum number of the electron in a shell is given by 2n2

➤Filling or orbitals in Atoms:

The filling of electrons into orbitals of different atoms takes place according to the Aufbau Principle, Pauli Exclusion Principle and Hund’s rule of maximum multiplicity.

According to Aufbau principle in the ground state of an atom, electron enters the orbital of lowest energy first and subsequent electrons enter in the order of increasing energies.

The lower the value of (n+l) for an orbital, the lower is its energy.

here l is the azimuthal quantum number and n indicates the principle quantum number

If two orbitals have same (n+l) value, the orbital with the lower value of n has lower energy.

Hund’s rule of maximum multiplicity deals with the filling of electrons into the orbitals belonging to the same sub-shell. According to this rule, electron pairing will not take place in the orbital of the same energy until each orbital is first singly filled with parallel spin.

➤Quantum Numbers:

Each electron in an atom is characterised by a set of definite values of three quantum numbers n, l and m. In addition of these three numbers, fourth quantum numbers is also needed which specifies the spin of the electron.

1. Principal quantum number (n):

Determines the main energy level of the shell in which the electron is present.

The various values of n are 1, 2, 3 and 4 etc. also known as K, L, M and N etc. respectively, as the value of n increases the energy of electron also increases.

2. Azimuthal quantum number (l) determines the sub-level or sub-shell (s, p, d and f) in a given principal energy level or shell to which an electron belongs.

3. Magnetic quantum number (m) gives information about the orientation of the orbitals.

Spin quantum number(s) describe the spin orientation of the electron; the electron can spin only in two ways, i.e. clockwise or anticlockwise.

4. Pauli Exclusion Principle:

It states that no two electrons in an atom can have the same set of four quantum numbers.

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