Static Electricity and Permittivity of a medium

Static Electricity 

Static electricity or electrostatics is the branch of science which deals with the phenomena related with electricity at rest.Generally an atom is electrically neutral i.e. in a normal atom the aggregate of positive charge of protons is equal to the aggregate of negitive charge of the electrons.

Some electrons are removed from the atoms of a body, then it is left with a preponderance of positive charge.It is said to be positively-charged.In other side , some electrons are added to it, negitive charge out-balances the positive charge and the body is said to be negitively charged.So in conclusion we can say that positive electrification of a body results from a deficiency of the electrons whereas negative electrification results from an excess of electrons.

Permittivity of a medium

A certain property of the medium called is permittivity, which acts key role. Every medium is supposed to possess through two permittivities, which are as follow.

1:Absolute permittivity

2: Relative permittivity

For measuring relative permittivity,vacuum or free space is chosen as the reference medium. It has an absolute permittivity of 8.854 x 10^–12 F/m

absolute permittivity     ε̻  =  8.854 x 10^–12 F/m

relative permittivity      ε_{r  = 1}

_{being a ratio of two similar quantities}  ε_{r  has no units.}

Now take any other medium,  If the relative permittivity , as compared to vacuum is ε_r 

_{Then its absolute permittivity is}  

                                                           

                                                       ε = ε̻ ε_r  F/m

 For example relative permittivity of Mica is 5 , then the absolute permittivity is

                        

                                                  ε = ε̻ ε_r  F/m  = 8.854 x 10^–12  x 5

                                                                         = 44..27 10^–12 F/m