“ELECTROSTATICS” in this branch of science we can study about rest charge. If charge at rest it give five property Electric field, Force, potential, capacitance, and potential energy.
charge is the fundamental physical property matter, it create different phenomena from initial. A scale can’t attract dust particle without rubbing by hair, in initial condition scale not attract dust particle.
History of charge
In 600 BC first of all “Thales” use charge word in his experiment, Thales of Miletus, one of the founders of Greek science, first noticed that if a piece of amber is rubbed with a woolen cloth, it then acquires the property of attracting light feathers, dust, lint, pieces of leaves, etc.
After this
In 1600 A.D. William Gilbert, the personal doctor to Queen Elizabeth – I of England, made a systematic study of the substances that behave like amber. In his book De Magnete (on the magnet), he introduced static electricity using amber; amber is called electron in Greek, so Gilbert decided to call its effect the electric force. He invented the first electrical measuring instrument, the electroscope, in the form of a pivoted needle he called the versorium.
Benjamin Franklin (1706-1790), an American pioneer of electrostatics introduced the present-day convention by replacing with silk bu the terms vitreous and resinous by positive and with flanne negative, respectively. According to this convention :
- The charge developed on a glass rod when rubbed with silk is called positive charge.
- The charge developed on a plastic rod when rubbed with wool is called negative charge.
gives a list of the pairs of objects which get matter, the po charged on rubbing against each other. On rubbing, an object of column I will acquire positive charge while bulk is electric that of column II will acquire negative charge.
electron charge
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Table : Two kinds of charges developed on rubbing
| (Positive charge) | (Negative charge) |
| Glass rod | Silk cloth |
| Woollen carpet | Rubber shoes |
| Flannel or cat skin | Ebonite rod |
| Woollen cloth | Amber rod |
| Woollen coat | Plastic seat |
Obviously, any two charged objects belonging to the same column will repel each other while those of two different columns will attract each other.
NOTE : Benjamine’s choice of positive and negative charges is purely conventional one.
Unit of charge
S.I / M.K.S. unit of charge is Coulomb “C”
C.G.S unit of charge is e.s.u ( electro state unit ) or su
smallest unit of charge is franklin “fr”
1 esu/su = 3*109 C
Charge in motion than its unit emu (electro magnetic unit )
1 emu of charge =10C
Biggest unit of charge is faraday “F”
1 F = 96500C / 1 F = 96550C