Page 147 - Science Class 08

at the same me, the silk acquires nega ve By Conduc on
charges. When an uncharged body is made in contact
with a charged body, the charge flows into the
uncharged body and the body is charged.

For example, if an uncharged sphere A is made
in contact with a charged sphere B, the sphere
A will be charged by sphere B, with the same
charge as in the sphere B.

Take a paper sheet and roll it into a hollow cylinder. This cylinder should not be very large. Tie
this cylinder at one end with a thread and suspend it from a stand. Now, charge an ebonite rod
by rubbing it with wool. We know that ebonite acquires nega ve charge. When we bring this
charged ebonite rod near the paper cylinder, the cylinder is a racted towards the rod. If we
touch the rod with the cylinder, the cylinder is repelled. Why suddenly the cylinder which was
a racted by the ebonite rod is repelled from it ? The answer is that some of the nega ve charge
that a racted the cylinder passed on to the cylinder from the rod on contact. The charged
objects (rod and cylinder) become same. The same charges repel each other. So, the similarly
charged paper cylinder is repelled by the rod. The

reverse phenomena happens when posi ve charged
glass rod is brought near the paper cylinder. The
cylinder can be tested for charge by bringing bits of
paper near it. If they cling to the cylinder, the
cylinder is charged.
The paper became charged on coming in contact
with rod. So, the objects can be charged when they
come in contact with another charged body. This
process of charging a body by contact is called
conduc on.

When a charged par cles or body is brought near uncharged body without touching, charges are
developed in the uncharged body. This method of charging a body is called charging by induc on.

To do this, the charged paper cylinder is brought near one end of uncharged ebonite or glass rod
suspended freely. The cylinder is either posi vely charged (+) or nega vely charged (–)
depending upon, it was touched by glass (+) or ebonite rod (+). Now, bring a charged (posi ve or
nega ve) rod near the other end of the suspended uncharged rod. The uncharged suspended
rod is that of glass while charged rod is of ebonite (nega ve charge). The paper cylinder is
charged nega vely by glass rod.
When nega vely charged ebonite rod is brought near the uncharged glass rod it is a racted
towards the ebonite rod.

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