some natural phenomena std 8th makwana gayatri

1. Chapter : 15
Some Natural Phenomena
Makwana Gayatri
B.Ed. trainee

3. In this presentation we
are going to explain
about the following
topics:
1. Introduction
2. Lightnings
3. Electrical charge
4. Transfer of charge
5. Electroscope
6. Earthquakes
7. Seismograph

4. Introduction
A natural phenomenon is not a man-made event.
Example include sunrise, weather, biological
processes, physical processes, tidal flow, and include
natural disasters such as electromagnetic pulses,
volcanic eruption , earthquakes.

5. Lightning
• Is a stricts of bright light and sound
caused by electric discharge between
cloud and Earth or between different
clouds.

6. Charging by rubbing
• Some object can be charged by rubbing with others objects.
When. Objects are rubbed, they attract light objects like
pieces of paper. This process is called charging by friction.
• E g. :- A plastic refill, scale or come when rubbed with dry
hair, paper or polythene gets charged and attracts prices of
paper.
• The charges acquired by rubbing are statics charges. They do
not move. When charges move, it is electric current.
• Electric current is the motion of charges through a
conductor.

8. Types of charges and their
interaction:-
• They are two types of
charges . They are positive
charge (+) and negative
charge (-).
• Two charges bodies may
attract or repel each other.
• Like (similar) charges repel
each other and unlike
(dissimilar) charges attract
each other.

9. Activity:-
• (a) Inflate two balloons. Hang them in such a way
that they do not touch each other.Rub both the
balloons with a woollen cloth and release them.
What do you observe?

10. • Now let us repeat this activity with the used pen refills.
Rub one refill with polythene. Place it carefully in a glass
tumbler using the tumbler as a stand . Rub the other refill
also with polythene. Bring it close to the charged refill. Be
careful not to touch the charged end with your hand. Is
there any effect on the refill in the tumbler? Do the two
attract each other, or repel each other?

11. • Rub a refill and place it gently in a glass tumbler as before .
Bring an inflated charged balloon near the refill and
observe.

12. What we are observed?
• A charged balloon repelled a charged balloon.
• A charged refill repelled a charged refill.
• But a charged balloon attracted a charged refill.

13. 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
aluminum foil. Pass one end of
the paper clip through the
cardboard and hung the two
aluminum strips from the other
end.
• If a charge body is touched to
the end of the paper clip, the
aluminum strips repel other.

15. Transfer of charge:-
• When a charge 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, 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.

16. 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.

17. Lightning:-
• During thunderstorms air currents move upwards
and water droplets move downwards. This
movement caused 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.

18. Lightning
• 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 sound
produced is called thunder. It was Benjamin Franklin
who first discovered that lightning was electric
discharge.

19. Lightning conductor
• A lightning conductor is a device used to protect
building from damage due to lightning.
• A lightning conductor has a metallic rod. The upper
end is pointed and the lower end is jointed to a
metal plate buried instead the ground.
• When lightning strikes, the electric charges pass
through it to the earth without causing any damage
to the building.

21. Protection of lightning and
thunderstorm
a) If you are outdoors:-
i. Open vehicles like motorbikes, trucks, open cars are not
safe.
ii. Open fields, Parks , elevated places, tail 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 filed stay away from trees, poles, metallic
objects. Do not lie down . Square on the ground with
hands on the knees and the head between the hands.

22. 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. Electric appliances like TV, computer, etc should
be unplugged.
iv. Bathing should be avoided to avoid contact with
running water.

23. Earthquakes
• An earthquake is a sudden shoking or trembling of the
earth caused by a disturbance deep inside the Earth's
crusts.
• Earthquakes caused damage to building, dams, Bridges. It
can cause landslides, floods and tsunamis . It can also
cause damage to life and property.

24. What cause an earthquake ?
• The outermost layer of the earth called crust is not
one piece. It is fragmented into many plates. This
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
seismic zone or fault zones. Earthquakes often
occur in the seismic zones.

26. • The seismic zones in India are Kashmir, Himalayas,
Info 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 Richter scale. Very destructive earthquakes
have magnitudes more than 7.5 on the Richter
scale.
• Earthquakes produce waves on the surface of the
earth called seismic waves.
• Seismic waves are recorded by an instrument called
seismograph.

29. Protection from earthquakes
i. The buildings in the 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.

30. Precautions during an earthquake
a) If you are at home:-
1. Take shelter under a table.
2. If you are in bed do not get up. Protect your head
with a pillow.
3. Stay away from tall and heavy objects which may
fall on you.
b) If you are outdoors:-
1. Find an open area away from buildings, trees and
power lines and lie on the ground.
2. If you are in a car or bus ask the driver to slow don
and don't get out till the tremors stop.

31. Seismograph
• Earthquakes generate seismic waves whii can be
detected with a sensitive instrument called a
seismograph
• Advances in seismograph technology have
increased our understanding of both earthquakes
and the earth itself.
• Perhaps the earliest seismograph was invented in
China A.D. 136 by a m an named choko.

32. Seismograph