Informational Encyclopedia

There is a charge of force around the medium, acts on a negative or positive charge when placed in the medium. If the charge is a huge , then it may create such a large stresses and causes the electrical damage to the medium, followed by the passage of an arc discharge.

The place in which the stresses leaves or in which the forces act, is called an electric field or electrostatic field.

These stresses are represented by imaginary lines of forces. The direction of the lines of forces at any points is the direction along with a unit positive charge placed at that point would move if free to do so. According to Faraday the electric field should be imagined to be divided into tubes of force consisting of fixed number of lines of force.

He considered these tubes having elasticity and the property of contracting longitudinally the repelling laterally. Fundamentals of this theory it becomes easy to explain 

(i) Why unlike charges attract each other and try to come nearer to each other.

(ii) Why same charges repel each other and try to go from each other.

However, it is more common to use the term lines of force. These lines are supposed to emanate from a positive charge and end on a negative charge. These lines always enter or leave a conducting surface normally.

It is a common practice when a charge body comes near uncharged body, it acquires some charge. This phenomenon of an uncharged body getting charge merely by the nearness of a charge body is called as induction. When a positively charged body A is placed close to the perfectly insulated uncharged body B, It is found that the end of B nearer to A gets negatively charged whereas further end becomes positively charged.

The positive and negative charge of B are known as induced charges. However the positive charge on the further end of B is called fee charge. In other figure when body B is earthed by a wire, the positive charge flows to earth leaving negative charge behind. If next A is removed, then this negative charge will also go to earth, leaving B uncharged. So the results are

(a) A positive charge induces a negative charge and vice-versa.

(b) Each of the induced charges is equal to the inducing charge.

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.

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