Some natural phenomena
There are so many natural phenomena in earth like cyclone, lighting and earthquake.
Lightning :- This phenomena is quite common when wind is blowing and shaking the wires. It is also an electric Spark but on a huge scale.
** In 1752 Benjamin Franklin, an American scientist showed that lighting and the spark from our clothes are essentially the same phenomena.
Charging by rubbing :- when a plastic refill is rubbed with polythene, it acquires a small electric charge. Similarly when a plastic comb is rubbed with dry hair, it acquires a small charge. These objects are called charged objects.
Tpyes of charge and their interaction :- There are two types of charge positive and negative.
** A charged balloon repelled a charged balloon.
** A charged refill repelled a charged refill.
** But a charged balloon attracted a charged refill.
It indicate that the charge on the balloon is of a different kind from the charge on the refill (one is positive and other is negative).
The electrical charge generated by rubbing are static. They do not move by themselves. When charge move they constitute an electric current.
Transfer of charge :- The Aluminium foil strips receive the same charge from the charged refill through the paper clip. The strip carrying similar charge repel each other and they become wide open.
Electroscope :- device can be used to test whether an object is carrying charge or not is known as electroscope.
Earthing :- The process of transferring of charge from a charged object to the earth is called earthing.
** Earthing is provided in buildings to protect us from electrical shocks due to any leakage of electrical current.
The story of lightning :- during the development of a thunderstorm, the air current move upward while the water droplets move downward. These vigorous movements cause separation of charges. The positive charge collect near the upper edge of the clouds and the negative charge accumulated near the lower edges. There is accumulation of positively charged near the ground also when the magnitude of the accumulated charge become very large, the air which is normally a poor conductor of electricity is no longer able to resist their flow. Negative and positive charge meet, producing streaks of bright light and sound. We see streaks as lightning. The process is called an electric discharge.
The process of electric discharge can occur between two or more clouds or between clouds and the earth.
Lightning safety :-
> A house aur a building is a safe place.
> We are traveling by car or by bus we are safe inside with windows and doors of the vehicle shut.
Do's and don'ts during a thunderstorm outside :-
> Open vehicle like motorbikes, tractors, construction machineries, open cars are not safe.
> Open fields, tall trees, Shelters in parks, elevated places do not protect us from lightning strokes.
> If in a forest, take shelter under shorter trees.
> If no shelter is available and we are in an open field, stay far away from all trees, poles or other metal objects.
Inside the house :-
> Lightning can strike telephone cords electrical wires and metal pipes.
> During the thunder storm contact with these should be avoided.
> It is safer to use mobile and cordless phones.
> Electrical appliance like computers TV's etc. should be unplugged electrical. Lights can remain on their, do not cause any harm.
Lightning conductor :- It is a device used to protect buildings from the effect of lightning. A metallic rod, taller than the building is installed in the walls of the building during its construction. One end of the rod is kept out in the air and the other is buried deep in the ground. The rod provides easy route for the transfer of electric charge to the ground.
Earthquake :- one natural phenomenon which we are not yet able to predict accurately, it is an earthquake. It can cause damage to human life and property on a huge scale.
** An earthquake is a sudden shaking or trembling of the Earth which lasts for a very short time.
** It is caused by a disturbance deep inside the earth's crust.
** Major earthquake are much less frequent.
** Earthquake can cause floods, tsunamis, landslides etc.
Cause of earthquake :- The outermost layer of the Earth is not in one piece. It is fragmented. Each fragment is called a plate. These plates are in continual motion. When they brush past one another or plate goes under another due to collision, they cause disturbance in the earth's crust. Which responsible for earthquake on the surface of the earth.
** The weak zones are known as seismic or fault zones.
** In India, the areas most threatened are Kashmir, Western and Central Himalaya, the wole of North East, Rann of Kutch, Rajasthan and the Indo gangetic plain.
Richter scale :- the power of an earthquake is expressed in terms of a magnitude on a scale called the Richter scale.
Protection against earthquake :-
(1) If we are at home :-
> Take shelter under a table and stay there till the shaking stops.
> Stay away from tall and heavy objects that may fall on you.
> If you are in bed, do not get up, protect your head with a pillow.
(2) if we are outdoors :-
> Find a clear spot, away from building, trees and overhead power lines. Drop to the ground.
> If we are in a car or bus, do not come out. asked the driver to drive slowly to a clearer spot.
(3) To build earthquake resistant houses.
(4) consult qualified architects and structural engineers.
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