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ELECTROSTATICS: When we discuss about static electricity also known as stationary charges and its laws, the branch of science is known as electrostatics.
PERMITTIVITY: This is the property of a medium for which the molecules of the medium oppose the external electric field.
Symbol of permittivity is Є
Every medium has two permittivities – i) absolute permittivity, ii) relative permittivity.
The absolute permittivity of vaccum or free space = 8.854×10-12 F/m.
Vaccum or free space permittivity is the refference for measuring relative permittivity. Being ratio relative permittivity has no unit.
Є = Є0Єr F/M
Let relative permittivity of an object is 4 then its absolute permittivity is Є = 8.854×10-12x4 F/M
= 35.416×10-12F/M.

Material Dielectric Constant or Єr
Vacuum 1.0
Glass 5-12
Mica 4-8
paper 2.6
water 80.1
Wood 2.5-7
Silicon 11.7

WHAT IS CHARGE?
This is fundamental property of a matter depends on electrons and protons.
There are two types of electric charge namely positive charge and negative charge. When electrons are removed from an uncharged atom, it became positive charge, whereas added electron makes an atom negatively charged.
The S.I unit of electric charge is Coulomb or AMP-HOUR (A-H).

ELECTRIC FIELD: The area surrounding an electric charge a force acts on another charge may be positive or negative of that medium for which an electric stress exists by the electric force, surrounding that charge.
The region where stress exists is called electric field or electrostatic field.

Electrostatics deals with forces between charges. Static charges are not moving or slow moving.
LAWS OF ELECTROSTATICS OR COULOMB’S LAW:
FIRST LAW: Like charges repeal each other whereas unlike charges attract each other.
SECOND LAW: Second law states that the force between charges is directly proportional to the product of their strength and inversely proportional to their square of the distance between them.
F∞Q1Q2/d2
Or, F= K Q1Q2/d2 Q1Q2 are charged particles.
d= diameter
In S.I system K= constant= 1/4πЄ0Єr Є= permittivity
=1/4Πx8.854×10-12
=9×109 (approx) N.
As, Є = Є0 Єr F/M
So, F= Q1Q2/4πЄd2=9×109Q1Q2/d2 N
Hence, one coulomb charge is that charge, when an equal and similar charge repeals it with a force of 9×109 N in a vaccum.

FIELD STRENGTH OR FIELD INTENSITY OR ELECTRIC INTENSITY (E):
Actually this is strength of any point inside an electric field.
The symbol is E and unit is Newton/Coulomb or Volt/m.
In an electric field this is nothing but a force experienced by unit positive charge placed at any point.
E=F/Q N per coulomb.
F=QX1/4πЄ0Єrd2 (for 1 coulomb positive charge)
Or, E=Q/4πЄ0Єrd2 N/C in a medium.
ELECTROSTATIC INDUCTION: An uncharged body getting some charge by a nearest charged body. This phenomenon is known as induction. If this phenomenon occurs in a static field, then it is called electrostatic induction.

Suppose a positive charge A brought nearer an uncharged body B, it is found that the site of B nearer to A gets negatively charged whereas other sites become positively charged due to induction.

The positive charge induces negative charge, on the other hand negative charge induces the positive one.
Each induced charges is equal to inducing charge.

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