Page 149 - Science Class 08

charge is more on an object the leaves will
open more. If the charge is less, then the leaves
will open less.
Flows of Charges— Conductors and Insulators
When electrons are deposited on certain
materials, they can make their way freely in
and but among atoms, In certain other
substances they cannot move freely. They
remain more or less at the some point on the
material at which they were deposited.
Substances that allow electrons to pass freely
through them are called conductors.
For example, copper, silver, iron, etc. There
are certain substances that do not allow
electrons to pass through them, these are
called insulators.
For example rubber, plas c, wood, etc:
Aim : To detect whether an object is
conductor or insulator.
Method:
Take two electroscopes. Charge the leaves of
one of them using an ebonite rod. Now,
connect the discs of the two electroscopes
using a copper wire. Remember, do not touch
the disc or copper wire with your hand.
You will no ce that the leaves of the second
electroscope will also diverge. The divergence
of the leaves of the first electroscope reduces.
This shows that some of the charge has been
transferred from the first to the second
electroscope, through the copper wire. Now,
repeat the experiment and connect the disc of
the electroscope using a plas c scale. The
leaves of the second electroscope do not
diverge at all. No charge is therefore,
transferred from the first to the second
electroscope. Thus, we can say that plas c is
an insulator.
Science-8
ELECTRIC CURRENT
Electric current is one of the most basic
concepts that exists within electrical and
electronic science— electric current is at the
core of the science of electricity.
Whether it is an electrical heater, a large
electrical grid system, a mobile phone,
computer, remote sensor node or whatever,
the concept of electrical current is central to its
opera on.
However, current as such cannot normally be
seen, although its effects can be seen, heard
and felt all the me and as a result it is
some mes difficult to gain a view of what it
really is.
When a charged electroscope is connected to
an uncharged electroscope through a copper
wire, charge flows from the charged to the
uncharged electroscope. This clearly shows
how electrons can flow from one charged body
to another uncharged body. This flow of
electrons is referred to as electric current. This
electric current is used in every household,
industries and other ins tu ons. You will read
more about how electricity is produced and
distributed in higher classes.
LIGHTNING
Induc on is the main cause behind many
natural phenomena. One of the best known of
these is the thunderstorm.
Benjamin Franklin first proved that clouds build
up charge during a thunderstorm. He showed
that lightning that we see in the sky is a very
heavy flow of charge between clouds.
How does Lightning Occur?
During a hot and humid day, air rises us rapidly.
As the warm and damp air rushes upward, it is
coilled by expansion and the water vapour in it
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