some natural phenomena

1. CHAPTER -15
SOME NATURAL PHENOMENA
Done by
v.sankara rama krishnan
viii ‘b’
Kendriya vidyalaya karaikudi

2. Some natural destructive phenomena are cyclones, lightning,
earthquakes etc.
Lightning is streaks of bright light and sound caused by electric
discharge between clouds and earth or between different clouds.
Earthquake is a sudden shaking or trembling of the earth caused by a
disturbance deep inside the earth’s crust. Lightning and
earthquakes cause a lot of damage to human life and property.
1) Somenatural destructive phenomena :-

3. 2) Charging by rubbing
Some objects can be charged by rubbing with other objects. When objects
are rubbed, they attract light objects like pieces of paper. This process is
called chargingby friction.
E.g. :- A plastic refill, scale or comb when rubbed with dry hair, paper or
polythene gets charge and attracts pieces of paper.
The charges acquired by rubbing are static charges. They do not move.
When charges move, it is electriccurrent.
Electriccurrent is the motion of charges through a conductor.

4. 3) Types of charges and their interaction:-
There are two types of charges. They are positive charge
(+) and negative charge (-).
Two charged bodies may attract or repel each other.
Like (similar) charges repel each other and unlike
(dissimilar) charges attract each other.
repels attracts

5. Charges acquired by different objects
A glass rod rubbed with silk gets positively charged.
A plastic rod rubbed with fur gets negatively charged.

6. Frictional orderFrictional order
Wool,Flannel,Fur,Sealingwax,Glass,Paper,Silk,Hand,Rub-
ber,Amber, Ebonite,Plastic.
When any of these materials are rubbed together, the
one in the higher order gets positive charge(+) and the one
in the lower order gets negative charge (-)frictional order
A glass rod rubbed with silk gets positive charge (+)
An ebonite rod rubbed with fur gets negative charge (-)

7. 4) Electroscope :-
An electroscope is a device used to test whether an object is having
electric charge or not.
A simple electroscope can be made by using an
empty bottle, a piece of cardboard, a paper clip and
two small strips of aluminium foil. Pass one end of
the paper clip through the cardboard and hang the
two aluminiun strips from the other end.
If a charged body is touched to the end of the
paper clip, the aluminium strips repel each other.

8. 5) Transfer of charge :-
When a charged body is brought in contact with an uncharged body
charges pass from the charged body to the uncharged body.
This method of charging a body is called charging by contact or conduction.
If a body is charged by contact it gets the same charge as the charged
body. We can observe the transfer of charge by using an electroscope. If a
charged plastic rod is brought in contact with an electroscope, the charges
are transferred to the metal strips and they repel each other.This is
because both the metal strips get the same charge and they repel each
other.

9. 6) Electric discharge :-
If we touch a charged electroscope with our hand, the charges pass
through our body to the earth and the metal strips collapse. This
property is called electric discharge.
The process of transferring electric charges from a charged body
to the earth is called earthing.
Earthing is provided in buildings to protect us from electric shock
due to leakage of electric current.

10. 7) Lightning :-
During thunderstorms air currents move upwards and water droplets
move downwards. This movement causes separation of charges in the
clouds. The positive charges collect at the upper part and negative charges
collect at the lower part of the clouds. Some negative charges collect near
the ground also. When a large amount of charge is formed, then the
charges pass from the clouds to the earth producing streaks of light and
sound. The light produced is called lightning and the sound produced is
called thunder.It was BenjaminFranklinwho first discovered that lightning was
electric discharge.

11. 8) Lightning conductor :-
A lightning conductor is a device used to protect buildings from
damage due to lightning.
A lightning conductor has a metallic rod. The upper end is pointed
and the lower end is joined to a metal plate buried inside the ground.
When lightning strikes, the electric charges pass through it to the
earth without causing any damage to the building.

12. 9) Protectionfromlightning and thunderstorm
veryvery important
a) If you are outdoors :-
i) Open vehicles like motorbikes, trucks, open cars are not safe.
ii) Open fields, parks, elevated places, tall trees are not safe.
iii) Carrying an umbrella is not safe.
iv) If in a forest take shelter under short trees.
v) If in an open field stay away from trees, poles, metallic objects. Do
not lie down. Squat on the ground with hands on the knees and
the head between the hands.
b) If inside the house :-
i) Lightning can strike electric wires, telephone cords and metal
pipes so contact with these objects should be avoided.
ii) It is safer to use mobile and cordless phones than wired phones.
iii) Electrical appliances like TV, computers etc should be unplugged.
iv) Bathing should be avoided to avoid contact with running water.

13. 10) Earthquakes
An earthquake is a sudden shaking or trembling of the earth caused
by a disturbance deep inside the earth’s crust. Earthquakes cause
damage to buildings, dams, bridges. It can cause landslides, floods
and tsunamis. It can also cause damage to life and property.

14. The outermost layer of the earth called crust is not one piece. It is
fragmented into many plates. These plates are moving continuously.
When these plates brush past each other or when one plate goes
under another plate due to collision, they cause disturbance and
causes earthquakes.
The boundaries of the plates are weak zones called siesmic zones or
fault zones. Earthquakes often occur in the seismic zones.
11) What cause an earthquake ?

15. The seismic zones in India are Kashmir, Himalayas, Indo Gangetic plane, North
eastern region, Kutch, Rajasthan, Andaman And Nicobar Islands some regions of
South India etc.
The power of an earthquake is measured on a scale called Richterscale. Very
destructive earthquakes have magnitudes more than 7.5 on the Richter scale.
Earthquakes produce waves on the surface of the earth called seismicwaves.Seismic
waves are recorded by an instrument called seismograph.
seismic zones

16. Seismiczones of India :-
karaikudi

17. 12) Protection fromearthquakes :-
i) The buildings in seismic zones should be designed such that they
can withstand tremors due to earthquakes.
ii) Materials like mud, wood and light roof should be used instead of
heavy materials.
iii) Heavy objects like cupboards, water heaters etc. should not be fixed
on the walls.
iv) All buildings should have fire fighting equipments.
Precautionsduring an earthquake :-
a) If you are at home :-
i) Take shelter under a table.
ii) If you are in bed do not get up. Protect your head with a pillow.
iii) Stay away from tall and heavy objects which may fall on you.
b) If you are outdoors :-
i) Find an open area away from buildings, trees and power lines and
lie on the ground.
ii) If you are in a car or bus ask the driver to slow don and don’t get
out till the tremors stop.

18. SIESMOGRAPH

19. SIESMOGRAPH

20. What you have learnt
 Some objects can be charged by rubbing with other
objects.
There are two kinds of charges — positive charge and
negative charge.
 Like charges repel and unlike charges attract each other.
The electrical charges produced by rubbing are called
static charges.
When charges move, they constitute an electric current.
An electroscope may be used to detect whether a body is
charged or not.
The process of transfer of charge from a charged object to
the earth is called earthing. The process of electric
discharge between clouds and the earth or between
different clouds causes lightning.

21. Lightning strike could destroy life and property.
 Lightning conductors can protect buildings from
the effects of lightning.
 An earthquake is a sudden shaking or trembling
of the earth.
Earthquake is caused by a disturbance deep
inside the earth’s crust.
 It is not possible to predict the occurrence of an
earthquake.
Earthquakes tend to occur at the boundaries of
earth’s plates. These boundaries are known as
fault zones.

22. Destructive energy of an earthquake is measured
on the Richter scale. The earthquake measuring
7 or more on Richter scale can cause severe
damage to life and property.
We should take necessary precautions to protect
ourselves from earthquakes.

23. Thanks
F r
watching