1.2 ELECTRIC CHARGE

The name electricity is coined from the Greek word elektron meaning amberIt was observed that if two glass rods  rubbed with wool or silk cloth are brought close to each other, they repel each other. However, the glass rod and wool attracted each other. Similarly, two plastic rods rubbed with cat’s fur repelled each other  but attracted the fur.It was concluded, after many careful studies that there were only two kinds of an entity which is called the electric charge The experiments on pith balls suggested that there are two kinds of electrification and we find that (i) like charges repel and (ii) unlike charges attract each other. The experiments also demonstrated that the charges are transferred from the rods to the pith balls on contact. It is said that the pith balls are electrified or are charged by contact. The property which differentiates the two kinds of charges is called the polarity of charge.the charges were named as positive and negative by the American scientist Benjamin Franklin.
FACTS
1.Charge is a derived scalar quantity, its dimensional formula is [AT].
2.Quantization of charge = it is found that charge on any body is always equal to integral multiple of charge of one electron . Charge can not be divided in random manner but can be divided in such a manner that both parts after division must be an integral multiple of elementary charge. This property of charge is called quantization of charge. q=n.e  here n=[+/-]1,2,3,4......[according to recent studies,protons,neutrons are also made of particles called as 'QUIARKS' having charges of [+/-]1/2e , [+/-]2/3e]
3. Conservation of charge=  For a given system the total charge is constant. let us take the the example of  a system of  a glass rod and silk.for this system total charge is constant,even if we rub them.Here glass rod becomes positively charge and silk negatively charged .Electrons from glass rod transferred to silk.This shows that charge can neither be created nor destroyed .it can only be transferred .
4.Unit of charge=
S.I unit =coulomb [C],   1C=6.25 × 10P[-25]
5. charge is always associated with mass. without mass charge does not exist.Partcles having zero rest mass are always chargeless.

STATIC ELECTRICITY