3. Electroscope

Types of Electroscopes

The two types of classic electroscopes that are still in use in the field of physics, help in explaining the concept of electrostatics are the pith-ball and the gold-leaf electroscopes.

The Pith-Ball Electroscope

It was invented by the British physicist and schoolmaster John Canton in 1754. It consists of one or two mini lightweight balls of non-conductive material, hung from the hook of an enclosed stand by the help of silk or linen thread.

In order to measure the presence of a charge on a material, hold the material closer to the uncharged pith-ball. If the test material charge is positive, then the electrons, i.e. negative charges in the molecules, would be drawn to it. They shift to the side of the molecules close the material. On the other hand, the positively charged molecule, i.e. the nucleus, repel and divert away from the material. This technique is useful to study the presence of electrostatic charge on the material with the help of pith-ball electroscope.

The Gold-Leaf Electroscope

It was invented by British physicist Abraham Bennet, in the year 1787 as a bit more sensitive tool compared to the Pith-ball electroscope.

The Gold-leaf electroscope serves to detect the electrical charge present in the body and to classify its polarity. Its works on the theory of electrostatic induction and repulsion. It consists of a single brass rod to which two slender gold leaves are attached to one end and metal disc at another end.

The two thin leaves and an electrically conductive material are hanged parallel to each other and practically in contact with each other. The rod is placed inside the cylindrical glass jar so that the gold leaves stay inside and disc lies outside. The lower portion consists of a tin foil and, a small amount of CaCl2 is placed inside the gold-leaf electroscope to keep the air inside the jar dry.

Since the leaves are fragile and sensitive, they don’t have any stiffness, and they hang timidly. When they charge, they divide and form an angle which depends on the amount of the impact on the leaves that determines the charge voltage. This electroscope only shows the potential, not the charge. Also, the voltage is measurable by studying the angle of separation.

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