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© Charge: Electric charge is an intrinsic property of elementary particles of matter which gives rise to electric force between various objects. Quantization : Charge is always in the form of an integral multiple of electronic charge and never its fraction. q= tne where 1 is an integer and e = 1.6 x 10-9 C. Millikan’s oil drop experiment showed the discrete nature of charge. Charge*cannot be fractional multiple of e. Conservation of charge : Net charge of an isolated physical system .always ~remains constant. Charge can neither be created nor destroyed. It can be transferred from one body to another. Electric charge is additive, ie, total charge is the algebraic sum of the individual charges. Electric charge is invariant as it does not depend upon the motion of the charged body or the observer. Coulomb’s inverse square law : It states that the electrostatic force of attraction or repulsion acting between two stationary point charges is given by Fe) 4h ANE, 7? where F denotes the force between two charges q, and q separated by a distance r in free space. €) is a constant known as permittivity of free space. Free space is vacuum and may be taken to be air practically. o Nm ines 10° ——_ Teg c? If free space is replaced by a medium, then Eq is replaced by (€,K) or (€y€,) where K is known as dielectric constant or relative permittivity. fo th 1 Nd. _ 1 Mh 4ne 7? 4me,K 7? 4mege, 9? K = 1 for vacuum (or air) and K = © for conductor/metal. &) = 8.85 x 10? C?2N'! mand its dimensig formula is (M?L?T'A?]. Vector form of the law (q, and qy are like charges) Nal (i) Fy = = 4, 4ne, % i (ii) 5, 1 ik + (% i, — 4192 1 a Ane, |%,-7 | ANE 1, > > Fi Py +32—______e» +4) +9, Electrostatic force due to continuous charge distribution The region in which charges are closely spaced is said to have continuous distribution of charge. It is of three types : Linear charge distribution dq=hdl where, A = linear charge density = ao Adl) ~ dF= 2040; _, p=} gold) * 4ney |r? 4ney [rf Net force on charge qo, F = —0_f dal r 4ney | Ir P Surface charge distribution +H tt + + “as | +, _ tht + do dE dq =o dS where, o = surface charge density Net force on charge qy, F =_7o_ ods- 4meyS |r P 
