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The woollen cloth (in case of umber), silk (in case of glass rod) and flannel (in case of ebonite rod) are also found to be charged with electricity. The electricity developed on bodies, when they are rubbed with each other is called frictional electricity. It is also called static electricity as the charges so developed on a body can not flow from one point to some other point. Two kinds of charges From experiments, it was concluded that frictional electricity is of two types. When a glass rod is rubbed with silk, glass rod is said to have become positively charged. As said earlier, the silk is also found to be charged with electricity. However, the nature of charge on silk is found to be opposite to that one glass and therefore silk is said to have become negatively charged. On the other hand, when ebonite rod is rubbed with flannel the charge on ebonite rod is found to be of same kind as of silk (when glass rod is rubbed with it). Thus, ebonite rod becomes negatively charged. When rubbed with flannel, while flannel it self becomes positively charged. Historically, charge produced on a glass rod, when rubbed with silk was called viterous and that produced on ebonite rod, when rubbed with flannel, was called resinous. Actually, the concept of positive and negative charges was introduced by Benjamin Franklin. Experiments proved that bodies having same kind of charge repel each other, while those having opposite kinds of charge attract each other. In the table given below, if a body in first column is rubbed against a body given in second column, body in first column will acquire positive charge, while that in second column will acquire negative large : The name of the body, which acquires Positive charge
Negative charge Glass rod
Silk cloth Flannel or catskin Ebonite rod Wollen cloth
Amber Woolen cloth
Rubber shoes Woolen cloth
Plastic object Obviously, if the two charged objects are from the same column,
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