An electroscope is a device which is used to detect the presence and magnitude of electric charge on a body. Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. ...
There are two types of electroscopes:
Pith ball electroscope
Gold leaf electroscope
Pith Ball Electroscope
Pith ball electroscopes consist of a light pith ball suspended by a silk thread from the hook of an insulated stand. In order to test the presence and magnitude of a charge on an object, the object is brought near to the pith ball without coming into physical contact with the object. If the pith ball is attracted to the object, the object's charge is opposite that of the pith ball, while if the pith ball is repelled, the two objects have the same charge (though not necessarily the same magnitude of charge). Silk is a natural protein fiber, some forms of which can be woven into textiles. ...
Gold Leaf Electroscope
The gold-leaf electroscope is an instrument used to identify the presence of charge on an object. The electroscope consists of an aluminium or brass rod at one end of which are fitted two pieces of gold coil or gold leaves and there is a metal disc at the other end. To protect the gold leaves from draughts of air they are enclosed in a glass bottle with a narrow mouth by fitting the metal rod in the ebonite stopper of the bottle. Nowadays aluminium foil is also used instead of gold.
When the metal disc is touched with a charged object the leaves of the electroscope spread out. This is beacuse the charge on the rod is conducted through the disc and brass rod to the leaves. As they receive the same kind of charge they repel each other and thus spread out. If one touches the brass rod with his finger the charge is transferred through his body into the earth and the leaves of electroscope then close together.
Volta made use of such an electroscope in his celebrated experiments (1790–1800) to prove that metals placed in contact with one another are brought to different potentials, in other words to prove the existence of so-called contact electricity.
To employ the electroscope as a means of detecting radio-activity, we have first to test the leakage quality of the electroscope itself.
Kelvin) that what a gold-leaf electroscope really indicates is the difference of potential between the gold-leaf and the solid walls enclosing the air space in which they move.' If these enclosing walls are made of anything else than perfectly conducting material, then the indications of the instrument may be uncertain and meaning-less.
In a calibrated electroscope, the two leaves are made of fine hammered gold leaf and the voltage is determined by viewing and measuring the separation angle with a low-power microscope.
All the important features of operation of the classical electrophorus may be demonstrated with an electroscope accessory mounted to a piece of aluminum or steel rod of minimum diameter 1/16".
A similar electroscope accessory can be made by bending the end of the wire opposite the leaves into the form of a horizontal base upon which the instrument sits upright.
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