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What is happening ?
Why is the paper attracted to the
pen or comb?
Why is the balloon attracted to
the sweater?
Static electricity
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How was electricity discovered?
Discovered by Thales (a Greek philosopher) in 600 B.C.
In 600 BC, the ancient Greek philosopher, Thales de Miletus discovered static
electricity. He observed that hard a yellow stone called amber had an enigmatic
property.
These developed electric charges remain on the object and do not move, it is said to
be stationary or static. This lead to the term “static electricity.”
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static electricity is observed when
a plastic comb is run through the
hair, and then is placed near small
pieces of paper.
The paper is attracted to the
comb. This happens because the
charged comb induces an
opposite charge in the paper and
as opposite charges attract, the
paper sticks to the comb.
Another c example is rubbing a
balloon against a woolen or
synthetic jumper.
Static Electricity
Video (static electricity): https://www.youtube.com/embed/3aB6TyhaSsQ
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What you understand by the term charging an object?
Brainstorming
How can you charge an object?
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Charging an object
Electric charges can neither be created nor destroyed
but can only be transferred from one object to
another.
This is called the law of conservation of charges.
There are three ways to charge an object. These are
friction,
conduction or
induction.
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Scientists have arranged different types
of materials in the order of their ability
to hold or give up electrons.
This ranking is known as triboelectric
series.
The triboelectric series is a list of
materials, showing which have a greater
tendency to become positively charged
and which have a greater tendency to
become negatively charged.
Triboelectric series
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Charging by conduction
The process of
charging in which
the object is
charged by
bringing another
charged object
in contact with it is
called as charging
by conduction.
This method is also
known as charging
by contact.
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Electroscope
Working of Electroscope:
When the brass disc of
the electroscope is
touched with a charged
object, the electric
charge gets transferred
to the gold leaf through
the rod.
This results in the gold
leave moving away from
each other. This happens
because both the leaves
have similar charges.
Electroscope is use to test for charges of a body.
Video (electroscope): https://www.youtube.com/embed/ectl3po7MuI
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Phenomena of Lightning
https://www.youtube.com/embed/RidvUkoNk3c
Video (Electricity and Lightening)
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The lightning strikes are accompanied by large amount of electric current and
heat. They can damage buildings, cause forest fires and kill people and animals
instantly.
Harmful effects of lightning
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During the earthquake there is a sudden
movement within the crust or mantle
and the concentric shock waves move
out from that point.
These waves are called seismic waves.
The origin of the earthquake is called
the focus.
The location of the earthquake is often
referred to as the point on the Earth’s
surface directly above the focus. This
point is called the epicentre.
Greatest damage from an earthquake
usually happens closest to the epicentre.
The strength of the earthquake
decreases away from the epicentre. The
whole phenomenon may last for just a
few seconds.
Earthquakes
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The instrument used to
measure seismic waves is
called a seismometer and the
scientists who study the
behaviour of earthquakes are
seismologists.
The magnitude of an
earthquake can be determined
from the data recorded by a
seismograph.
The most common scale used
to measure the magnitude of
an earthquake is the Richter
scale.
Measuring Earthquakes
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1. Which one of the following devices is used to detect electric charge on an object?
(a) Seismograph
(b) Seismometre
(c) Ritcher scale
(d) Electroscope
2. Lightning occurs due to
(a) wind
(b) rain
(c) electric discharge
(d) earthquake
QUIZ
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3. The point from where the shock waves of an earthquake originate is called
(a) epicentre
(b) focus
(c) focal depth
(d) none of these
4. If two charged objects are brought close to each other then
(a) they will attract each other.
(b) they will repel each other.
(c) they may attract or repel depending on the charges they carry.
(d) there will be no effect between them.
QUIZ
