LECTURE - 3 : CLASS VIII : SCIENCE : CHAPTER 15 : SOME NATURAL PHENOMENA

SEISMIC ZONES OR FAULT ZONES:

The weak zones of earth's crust which is more prone to earthquakes are called seismic zones. It is also known as fault zones. 

In India, the areas most affected or threatened by earthquakes are Kashmir, Western and central Himalayas, the whole of North-east, Rann of Kutch, Rajasthan and Indoh gangetic plane. Some areas of South India is also prone to earth-quakes. 

SEISMOGRAPH: THE EARTHQUAKE MEASURING INSTRUMENT.

Seismograph is an instrument which measures and records the magnitude of an earthquake in terms of the shock waves it produces. 

Construction of Seismograph or Seismometer:

A seismograph consists of a heavyweight like a heavy metal ball suspended from a support with the help of a strong wire. The support is attached to the base of the seismograph and the base is rigidly fixed to a solid rock on the surface of the earth. A pen is attached to the the lower end of the hanging heavyweight.  It is used to draw graphs on the graph paper which is wrapped around a rotating drum. When earthquake occurs the pen draws graphs on the graphsheets due to the oscillation of the heavy object. From this graph we can measure earthquakes.

FOCUS AND EPICENTER OF EARTHQUAKE:

The place inside the earth's crust where the earthquake is generated, is called 'focus' of the earthquake. 

The point on earth's surface directly above the focus is called epicenter. 

MAGNITUDE OF EARTHQUAKE AND RICHTER SCALE:

The magnitude or intensity of an earthquake is expressed on the Richter Scale.

In a Richter scale 1 to 12 numbers are assigned to express the magnitude of an earthquake. 

Suppose the magnitude of an earthquake is 3 on the Richter scale, and magnitude of another Earthquake is 4 on the Richter scale, then the second earthquake is 10 times more intense than first earthquake. 

The magnitude of earthquake having 4 in Richter Scale is ten times more than the magnitude of the Earthquake having 3 on the Richter scale.

The Earthquakes having magnitudes higher than 7 on the Richter Scale are called destructive Earthquake. 

PROTECTION AGAINST EARTHQUAKE:

Earthquakes are highly destructive and it cannot be predicted. Therefore, we should always take some precaution against earthquake.

1. All the houses and other buildings in seismic zones should be designed and constructed in such a way that they can with stand measure earthquake tremors.

2. In highly systemic areas the use of mud and timber for building houses is better than using heavy construction materials. 

3. The cupboards and shelves should be fixed to the world's so that they do not fall easily when shaking occurs during an earthquake. Glass bottles should not be placed on high shelves and heavy objects should be placed low to the ground.

4. The objects such as heavy mirrors, photo frames, wall clocks and water heaters should be mounted securely on the world at such places in the house that they do not fall on the people in the house in the event of an earthquake.

5. All buildings should have fire fighting equipment in working order because some buildings may catch fire during an earthquake due to electric short circuits. 

PRECAUTIONS TAKEN WHEN EARTHQUAKE OCCURS:

A. If we are at home when an earthquake occurs.

We should take the following precautions.

1. We should take shelter under a study table for a kitchen counter and stay there till the shaking due to earthquake stops and we should cover our head with hands.

2. We should stay away from tall and heavy objects so that if they topple they may not for on us. We should also stay away from glass windows that may shatter due to vibrations.

3. If we are in bed, we should just move on the bed to be close to a wall but not get up from the bed. We should protect our head with a pillow.

B. If we are outdoors when an earthquake occurs.

We should take the following precautions.

1. We should stay at a clear spot away from buildings, trees and overhead power lines etc. We should also seat on the ground.

2. If we are in a car or bus, we should not come out of it. The car or bus should be driven slowly to a clear spot away from buildings, trees and overhead electric wires etc. We should not come out of the vehicle till the tremors stop.

LECTURE - 1 : CLASS VIII : SCIENCE : CHAPTER 18 : POLLUTION OF AIR AND WATER

POLLUTION AND POLLUTANTS:

Pollution: The presence of harmful or toxic substances in our surroundings is called polition. Our surroundings includes air, water, soil, sound etc. 

Pollutant: An unwanted and harmful and poisonous substances that contaminates the environment is called pollutant. Pollutant are also called contaminant. 

AIR POLLUTION:

 Air:  Air contains Nitrogen, Oxygen, carbon di oxide and other gases like argon and water vapour. 

Carbon monoxide, sulphur di oxide, nitrogen di oxide and other oxides of nitrogen, smoke, dust they are the most common pollutants of air. Fly ashes are also an air pollutant. 

Air pollution: 

The contamination of air with harmful gases like Sulphur dioxide, nitrogen oxides, carbon monoxides, smoke, dust etc is called air pollution. 

Air pollutant: Carbon monoxide, sulphur di oxide, nitrogen di oxide and other oxides of nitrogen, smoke, dust they are the most common pollutants of air. Fly ashes are also an air pollutant. 

SOURCES OF AIR POLLUTION:

1. Burning of fossil fuels (kerosene, petrol, diesel) , wood, cow dung cakes in home produces smoke, which is an air pollutant.

2. Exhaust gas from motor vehicles are also polluting the air.

3. Industrial factories has chimney which produces thick smoke also pollutes air.

4. Oil refineries which produces petrol, diesel and other petroleum products also pollutes air. Chemical factories also pollutes air.

5. Cement, asbestos factories and stone crushers also pollutes air.

6. CFC (chloro-fluoro carbons) used in refrigerator and air conditioner harm the ozone layer of atmosphere, which protects us from ultra violet rays. 

7. Smoking also causes air pollution. 

COMMON AIR POLLUTANTS:

1. Sulphur di oxide: SO₂ 

When petrol and diesel burns it produces sulphur di oxides. It creates respiratory problems in human beings. It can damage the lungs permanently. Due to the presence of Sulphur di oxide, acid rain occurs. 

Effect: Sulphur dioxide in air causes respiratory problems. It may even cause permanent lung damage. It causes acid rain and acid rain damages trees, plants, soil, aquatic animals, statues, buildings and historical monuments.

SMOG: 

Smog is a deadly air pollutant which is formed by the combination of smoke and fog. When smoke, and dust mixed with water droplets and water vapour present in atmosphere (Fog), it produces smog. Sulphur di oxide also contributes in smog. 

Effect: Smog causes cough and and other lung diseases especially in children.

Nitrogen oxides: 

Burning of fuels like petrol and diesel produces nitrogen oxides. Nitrogen oxide attack breathing system and lead to lung congestion. They also attack skin. Nitrogen oxides present in polluted air produces a acid rain. It also contributes to the formation of smog. 

Effect: Nitrogen oxides attack breathing system and lead to lung congestion. They also attack skin.

Carbon monoxide: CO

Incomplete combustion of fuels produces carbon monoxide. The exhaust gases of motor vehicles also produces carbon monoxide.

Effect: Carbon monoxide combines with the hemoglobin of our blood and reduces the oxygen carrying capacity of blood this lack of oxygen causes respiratory problems or breathing problems. it causes suffocation. 

Chlorofluorocarbons: 

Chlorofluorocarbons are used in refrigeration air conditioning and aerosol sprays. Chlorofluorocarbons are depleting the useful ozone layer of the upper atmosphere. Ozone layer prevents the harmful ultraviolet radiations of the sun from reaching to the earth. Effect: Destruction of ozone layer by CFC allow extremely harmful ultraviolet radiations of the sun to reach the earth. This ultraviolet radiations can cause skin cancer cataract and destruction of plants including crops. 

Suspended particulate matter or SPM: 

The finely divided solid or liquid particles suspended in air are called suspended particulate matter. Some of the examples of suspended particulate matter are dust, smoke and fly ash. 

1. Dust: Dust consists tiny particles of Earth.

Effect: Dust produces allergic reaction in human body and aggravates diseases like bronchitis. Dust covers the leaves of plants and trees and prevents photosynthesis.

2. Smoke: Smoke is mainly tiny particles of carbon in air.

Effect: Smoke attacks our lungs and causes respiratory diseases.

3. Fly ash: The minute particles formed by the burning of coal and carried into Air by the gases produced during burning is called fly ash.

Effect: Fly ash particles present in air cause irritation to the eyes skin nose throat and respiratory tract. Continued breathing in air containing fly ash causes diseases like bronchitis and lung cancer. 

EFFECTS OF AIR POLLUTION:

The two extremely harmful effects of air pollution on the environment are acid rain and greenhouse effect. 

ACID RAIN: Acid rain is that rain which contain small amounts of acids formed from acidic gases like sulphur dioxide and nitrogen oxides present in polluted air. Acid rain contains very dilute solutions of sulphuric acid and nitric acid. Acid rain causes great damage to living and non-living things.

Effects: There are several harmful effects of acid rain. They are as followings.

1. Acid rain destroys forests.

2. Acid rain kills aquatic animals such as fish.

3. Acid rain corrodes the statues buildings and historical monuments and damages them slowly. 

TAJ MAHAL AND ACID RAIN:

The Taj Mahal at Agra is a beautiful historical monument made of pure, white marble. Extreme air pollution around Taj Mahal area is this colouring its white marble and also corroding it slowly. 

Marble cancer:

The acids present in acid rain react with the marble (calcium carbonate) of Taj Mahal monument and corrode it slowly. The slow corrosion of marble of a monument by acid rain is also known as marble cancer.

Discolouring of Taj Mahal:

The suspended particulate matter such as soot particles emitted in the smoke from Mathura oil refinery is discoloring the pure white marble of Taj Mahal by turning it yellowish.

Preventive measure taken to save Taj Mahal:

The supreme court of India has taken several steps to save Taj Mahal from the damage being caused by air pollution and acid rain. It has ordered all the industries in Agra area to switch over to cleaner fuels like CNG and LPG to reduce air pollution. It has also asked vehicles to be run on CNG or unleaded petrol in the Taj Mahal area. 

GREENHOUSE EFFECT:

1. Greenhouse: 

The greenhouse is a structure or building made of glass walls and glass roof in which the plants that need protection from cold weather are grown. The glass walls and glass roof of a greenhouse allow the sun's rays to go in freely but do not allow the inside heat reflected by soil, plants and other things in the greenhouse to go out.

2. Greenhouse effect:

Due to the presence of carbon dioxide layer around the earth, our atmosphere acts like the glass roof of an ordinary greenhouse and allows sun's heat rays to be trapped within the earth's atmosphere. The warming up or heating up of the earth's atmosphere due to the trapping of sun's heat rays by carbon dioxide gas in the atmosphere is called greenhouse effect.

3. Global warming:

The rise in the temperature of Earth's atmosphere due to excessive greenhouse effect produced by increasing amounts of carbon dioxide gas in the atmosphere is called global warming.

4. Effects of global warming:

1. Global warming can cause sea levels to rise dramatically.

2. Global warming can reduce rainfall in some areas of the earth leading to droughts. 

3. Global warming is a serious threat to the existence of life on earth.

5. Greenhouse gases:

Those gases which can trap sun's heat rays in the earth's atmosphere by producing greenhouse effect leading up to the heating of Earth's atmosphere are called greenhouse gases. Carbon dioxide, Methane, Nitrous oxide, Chlorofluorocarbons and Water vapour are all greenhouse gases.

HOW TO CONTROL AIR POLLUTION:

There are several ways to control air pollution. 

1. The air pollution can be controlled by using smokeless waves like LPG, PNG, solar cookers and biogas for cooking food. 

2. The air pollution from motor vehicles can be reduced by using CNG or compressed natural gas is filled in place of petrol and diesel.

3. The air pollution from factories, thermal power plants, oil refineries and chemical industries can be controlled by washing down their smoke and waste gases with jets of water.

4. The air pollution can be controlled by using non polluting sources of energy like solar energy wind energy hydro energy for generating electricity.

OUR ROLE IN CONTROLLING AIR POLLUTION:

1. We should not burn dry leaves, papers and garbage in the open.

2. We should save electricity.

3. We should grow more trees and also take care of the existing trees in our neighborhood.

4. We should join "say no to crackers" campaign.

5. We should use bicycle for covering short distances.

6. We should use the school bus or public transport bus for going to school.