First we see that, What is the electroscope?
ð An
electroscope is a scientific device / instrument used to detect the presence of
Electric Charge on any body.
It detects electric charge by the movement of body (test
body). This is possible due the Coulomb Electrostatics Force.
Gold-Leaf Electroscope:-
“It is a instrument for detecting presence of electric charge.
In which a metal disc is connected to one end of a narrow metal rod(Brass Rod)
and a this piece of gold leaf is fixed to the other end.”
The old-leaf
electroscope was developed in 1787 by British physicist Abraham Bennet.
In this
electroscope, the whole assembly (metal disc, metal rod and piece of gold leaf)
is insulated from the body of the instrument. To protect the leaves from the
drafts of air they are enclosed in a Glass bottle, usually this bottle is open
at the bottom and mounted over a conductive base. The glass allows to observe
the effect of charge on the leaf.
Working :-
When a charge
is put on the disc at the top it spreads down to the plate and leaf moves away
from the plate. This is because some of the charge on the object is conducted
through the terminal and metal rod to leaves. Since they receive the same sign
charge, due to this they repel each other and diverge.
The leaf
can be made to fall again by touching the disc. If the terminal is grounded (fall
down) by touching it with a finger, the charge is transferred through the human
body into the earth and the gold leaves close together.
The electroscope can be charged in two ways,
a) By contact- a charged rod is brought in contact with the disc and charged is transferred to the electroscope. This method gives the gold leaf the same charge as that on the conductor. This is not a very effective method of charging the electroscope.
b) By induction - a charged rod is brought close to the disc (not touching it) and the electroscope is earthed. The rod is removed. This method gives the gold leaf opposite charges.
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