Organic Evolution

More and more creation of organism by gradual changes from low categories animal to higher animal is called organic evolution. There are several evidence regarding organic evolution.

Homologous organ : Organ which are seen different due to use in various function but its structure and embryonic embryonic development are similar.
Example - Flipper of Whale, featurer of bat, forlimb of horse, Paw of cat and hands of human.

Analogous organ : Organ which looks similar due to be used in similar function but their internal structure and embryonic development are different.
Example - feature of butterfly, bats and birds all looks similar but their internal structure and origin are different.

Vestigial organ : These are organs which appear functinless in an organism but functional in their ancestor.
Example - vermiform appendix of large intestine and nictitating membrane of human. Vermiform appendix is functional in herbivorous mammal even now.

Fossils : Fossils are the remains of ancient plant or animal which provide evidence for evaluation. Example - Archaeoptery.

Archaeopteryx : It is a fossils look like bird but near a number of features found in reptiles. So, it is a connecting link between aves and reptile.

Organic Evolution

Carbon and its Compounds

Carbon : Carbon is non-metal having atomic number 6 and mass number 12. It is placed in group (IV) A or group 14 in periodic table.

Allotropy : The substances which have same chemical properties, but different physical properties are called Allotropy.

Example : Allotropis of Carbon - Diamond, Graphite, Charcoal.

Diamond : Diamond is the purest form of carbon. It is the hardest natural known substance. It is transparent, and specific gravity 3.52. It is bad conductor of electricity and heat.

Diamond has very high refractive index 2.415. It is chemically inert and on heating above 1500°C, transferred into graphic. It form tetrahedral crystals and subsidization of C-atom is sp raise to the power 3.

Diamond has high mp and density. Black diamonds called carbonado contains traces of graphite.

Graphite and Diamond

Graphite : Graphite is soft, greasy, dark greyish colored crystalline solid. It is good conductor of heat and electricity. Its specific gravity is 2.3. The hybridization of carbon is graphite is sp2 and it has hexagonal layer structure.

Graphite is chemically more reactive than diamond. Its layer structure is held by weak van der waal's force.

Graphite is used in making for lining and making electrodes of electric furnances, in making refractory crucible, in making lead pencils, as a moderator in nuclear reactor as lubricant in machinery, as a reducing agent in steel manufacturing.

Orbital speed of a satellite

Orbital speed of a satellite is independent of its mass. Hence satellites of different masses revolving in the orbit of same radius have same orbitational speed. Orbitational speed of a satellite is depends upon the radius of orbit. Greater the radius of orbit, lesser will be the orbital speed.

»» The orbital speed of a satellite revolving near the surface of earth is 7.9 km/sec.

Period of Revolution of a satellite : Time taken by a satellite to complete one revolution in its orbit is called its period of revolution.

i.e. period of revolution of = circumference of orbit / orbital speed

Period of Revolution of a satellite depends upon the height of satellite from the surface of earth. Greater the height, more will be the period of Revolution. Period of Revolution of a satellite is independent of its mass.

»» The period of Revolution of a satellite revolving near the surface of earth is 1 hour 24 minutes.

Unemployment

In common parlance anybody who is not gainfully employed in any productive activity is called unemployed. However, it can be of two kinds :
(i) Voluntary Unemployment

Unemployment

(ii) Involuntary Unemployment

Here we are concerned with the second category of unemployed persons.

Hence, unemployment can be defined as a situation when persons able and willing to work are seeking jobs at the prevailing wage level but they are unable to get the same.

Types of Unemployment :

(1) Cyclical Unemployment : It is the result of depression in an economy.

(2) Frictional Unemployment : This kind of Unemployment is temporary. It is result of a situation when new industries drive out old ones and workers change over to better jobs.

(3) Open Unemployment : It refers to those who have no work to do even though they are able and willing to do work.

(4) Seasonal Unemployment : This occurs at certain period of the work when work load is comparatively less, and hence people are rendered jobless.

(5) Educated Unemployed : This is mainly found in urban areas. Those educated persons who are unable to get work come under this category.

(6) Disguised Unemployment : It results when a person contributes to production less than what he or she is capable of, for example an engineer working as a clerk under employed.

(7) Compulsory Unemployment : It means the labour power which is ready to work on the current rate but does not get the work.

The Sun

The Sun is at the center of the Solar System. Its size is thirteen lakh times as that of the Earth. It is the nearest star to Earth. It is an ultimate source of energy for life on Earth. Its diameter is 14 lakhs kms.

It is composed of 17% Hydrogen, 26.5% Helium and 2.5% other elements. Hydrogen and Helium are the main gases present in the Sun. Within the Sun, hydrogen is converted to Helium due to nuclear fusion releasing a tremendous amount of heat and light.

The Sun

It has a surface temperature of about 6000°C. The temperature at the center is around 15,000,000°C. Shining surface of the Sun is called photosphere, it appears like a disc, radiates energy and acts as a source of energy.

The outer layer of Sun's atmosphere made up of thin hot gases, is called Corona. Corona is visible only during a total eclipse of the Sun or with a special solar telescope called Coronagraph.

The planet travels with the Sun through millions of stars in our galaxy at a speed of about 70,000 km per hour. The Sun is about 150 million kms away from the Earth. Light takes about 8.5 minutes to reach the Earth from the Sun at the speed of 300,000 km per second.