movement of electric charge through them, insulators do not. In metals, the mobile charges are electrons; in electrolytes both positive and negative ions are mobile. . Electric charge has three basic properties: quantisation, additivity and conservation.
Quantisation of electric charge means that total charge ( q ) of a body is always an integral multiple of a basic quantum of charge ( e ) i.e., q = n e , where n = , ± , ± , ± , .... Proton and electron have charges + e , – e, respectively. For macroscopic charges for which n is a very large number, quantisation of charge can be ignored. Additivity of electric charges means that the total charge of a system is the algebraic sum (i.e., the sum taking into account proper signs) of all individual charges in the system.
Conservation of electric charges means that the total charge of an isolated system remains unchanged with time. This means that when bodies are charged through friction, there is a transfer of electric charge from one body to another, but no creation or destruction of charge. . Coulomb’s Law : The mutual electrostatic force between two point charges q and q is proportional to the product q q and inversely proportional to the square of the distance r separating them.
Mathematically, F = force on q due to ˆ k (q q ) where ˆ r is a unit vector in the direction from q to q and k = ε is the constant of proportionality. In SI units, the unit of charge is coulomb. The experimental value of the constant ε is ε = . × – C N – m – The approximate value of k is k = × N m C – .
The ratio of electric force and gravitational force between a proton and an electron is e p k e . G m m ≅ . Superposition Principle : The principle is based