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Charge UDIT GUPTA ALUMNUS MNNIT ALLAHABAD EX-VMC FACULTY OF PHYSICS
Defining electric charge If we start dividing a material into its constituent particles (elementary particles), we reach three elementary particles that constitute a nucleus- electron, proton and neutron. Since all these particles carry mass, there is a force of attraction between them given by Newton's law of gravitation. Gm1m2 2
Defining electric charge We also notice that when two electrons are placed close to each other there is a repelling force on both which tells us that there must be an extra force coming into play known as electric force. This force is generally very large as compared to the gravitational force. The property attributed to the presence of this electric force is called charge. A similar property was observed in case of protons as well. No such e came into play when we studied neutrons.
Types of charge We know that a repelling electric force acts between two electrons or two protons. The force, however, becomes attracting in nature when we place a proton near an electron This brings us to the point that although the two entities are charged, there must be some difference to account for the attracting nature.
Types of charge This brought us to a conclusion that electron and proton have different charge and that causes difference in types of force. We arbitrarily chose the charge on electron to be negative and that on proton to be positive. This does not mean that electron has a "lesser" charge than proton
Units of charge The S.I. unit of charge is Coulomb (C) By definition we say, the charge passing through a wire is 1C if a current of 1A is flowing for 1s through it. The charge on a proton is e = 1.6 10-1%. The charge on an electron is-1.6 10-1%.
Quantization of charge The fact that charges occur in form of electron and proton means that charge can only exist as an integral multiple of 1. 6 x 10-19c, or we say charge is quantized. If we say that an object has a charge 2.4 x 10-19C, it is not possible. The reason is that for this amount of charge, there must be 1.5 protons and this violates quantization of charge.