The Atmosphere

The air is composed mainly of nitrogen (78%) and oxygen (21%) with small proportions of carbon dioxide, water vapour and rarer gases like argon and neon. Atmosphere is 200 miles thick, but nine-tenths of the air composing it is found within 12 miles, and half within 3½ miles of the earth’s surface. We are concerned mainly with the lower layer of troposphere. The upper layers in the ascending order are Stratosphere, Mesosphere and Ionosphere. Troposphere extends to a distance of about ten kilometres. Stratosphere is a region extending from an altitude of about 11 Km to 50 Km above the earth. The upper part of stratosphere has plenty of ozone which protects us from the fatal effects of Sun’s ultraviolet radiation. Mesosphere is the next layer extending from 50 to 80 Kms above the earth. It is a very cold region. Ionosphere extends from about 60 Kms upwards. It includes Thermosphere and Exosphere which marks the outer limits of the earth’s atmosphere.

Why is rainbow seen after rain?

After a rainfall, the clouds break and lie hanging in the sky and the sun is also visible. The Sun’s rays, falling on the water drops, are dispersed, totally reflected at the back of the drops and then again refracted into the eye of the observer with his back towards the sun. These dispersed rays which have suffered deviation give rise to a concentrated beam of light indicating all the colors of light.

SOCIAL DISEASES

Alcoholism :
It is a social disease. It ruins the health of the people and causes a loss of manpower and hampers economic progress. It may lead to increased accidents, social crimes and other illegal activities. People start with small quantities out of curiosity and pleasure and soon become addict to it and take to heavy drinking.

Drug addiction :
Primarily drugs are meant for treatment of a disease. But sometimes people start taking drugs even though they don’t have any disease. They do so for excitement or pleasure or to relieve themselves of mental
tension. Constant and regular use of these drugs forms a habit and once acquired, it becomes very difficult to
get rid off this habit. This condition is called Drug Addiction. Like alcoholism it is also a social disease.

SCIENTIFIC LAWS

Archimedes’ Principle: It states that a body, when immersed in a liquid, experiences an upward thrust equal to the weight of the liquid displaced by it.

Avogadro’s Hypothesis: It is a modification of Berzelius’ hypothesis. It states that equal volumes of all gases
under similar conditions of temperature and pressure contain equal number of molecules.

Boyle’s Law: States that the volume of certain gas is inversely proportional to the pressure at a constant
temperature. In other words, the product of pressure and volume remains constant provided the temperature
ratios to one another and also to the volumes of the
products, if gaseous - all the volumes being measured
under similar conditions of temperature and pressure.

Graham’s Law of Diffusion : States that the rates of diffusion of gases are inversely proportional to the square roots of their densities under similar conditions of temperature and pressure.

Law of Definite Proportions : A chemical compound is always found to be made up of the same elements
combined together in the same ratio by weight.

Law of Floatation : For a body to float, the following conditions must be fulfilled:
(1)The weight of the body should be equal to the weight of the water displaced.
(2) The centre of gravity of the body and that of the liquid displaced should be in the same straight line.

Newton’s Law of Universal Gravitation : States that “Every portion of matter attracts or tends to approach
every other portion of matter in the universe with a force proportional to the masses and inversely as the
square of the distance”.

Newton’s First Law of Motion : A body continues in its state of rest or of uniform motion in a straight line
unless compelled by an external force to change that state.

Newton’s Second Law of Motion : The rate of change of momentum is proportional to the impressed force
and takes place in the direction of the force.

Newton’s Third Law of Motion : To every action, there is an equal and opposite reaction, e.g. Rockets, recoil of a gun.

Newton’s Law of Cooling : States that the rate of loss of heat of a hot body is directly proportional to the difference of temperature between the body and the surrounding and is independent of the nature of the body.

MEASUREMENT UNITS

Angstrom : For measuring length of light waves.
Barrel : For measuring liquids. One barrel is equal to 31½ gallons or 7,326.5 cubic inches/
Cable: For measuring length of cables. It is about 183 m. in length.
Carat : Used for measuring precious stones. It is also a measure for the purity of gold alloy.
Fathom : It is used for measuring depth of water. One fathom is equal to 4 inches.
Knot: For measuring speed of ships.
Horse Power : Used for measuring the power of petrol or steam engine.
Light Year : A light year is the distance light travels in one year at a speed of 2,97,600 km per second.
Nautical Mile : A unit of distance used in navigation - one minute of longitude measured along the equator.
A Nautical Mile is approximately equal to 1853 metres.
Ohm : The unit of electrical resistance of a conductor.
Quintal : Metric measure of weight, 100 kilograms = 1 Quintal.