# Physics:class 12th board notes

Coulomb's law
=How an electric force behaves between like or opposite charges,and its dependencies on separation distance and charge magnitude . Compare the electric force and gravitational force.

|FE |=k |q1q2/r^2/

Where :-
|FE |is electric force,
K is the Coulomb's constant ,
q1 and q2 are charges,
R is the distance between charge,

The magnitude of the electric force between q1 and q2 is directly proportional to the charge and inversely proportional to the square of the distance between them .This equation is known as Coulomb's law.

Electric Force
:-The attractive or repulsive force between two charged objects.sometimes called electrostatic force.vector quantity with the units N.

|FE |=k|q1q2/r^2|        |Fg | =G  m1m2/r^2

*Fg uses G and FE use k where k=
K =9.0×10^9 N.m^2/c^2

Gravitational force always act as attractive where as Electric force behaves as both attractive and repulsive. Two same charge repulse and two different charge attract each other.

Ef is inversely proportional to r^2 instead of r . As the distance between charges increase,the EF decreses by factor of 1/r^2.

E.g :- If we double the distance between two electron the repulsive force between them would reduce and it would go down by factor og 4 instead of 2.

*Vactor forms of Coulomb's Law

F=q1q2/d2

F=1/4πE●Er . q1q2/d^2
F= 1/4πE . q1q2/d^2

Where,
E is absolute permittivity,
K or Er the relative permittivity or specific inductive capacity,
K or Er medium also called a dielectric constant of the medium in which the two charges are placed.
F12= force q1 due to q2
=Kq1q2/r^2 r21

*Superposition
The principal of superposition states that,when two or more waves of the same point ,the resultant displacement at that point is equal to the sum of displacement due to each individual wave.

Intensity =E = A^2

The resulting intensity at the point of intersection can be greater or smaller than the intensity due to each the superposing waves.

F1 = F12 + F13 +.........F 1N

*Electric field
It is defined as the electric force per unit charge . The direction of the field is taken on a positive test charge. The electric field is radially outward from a positive charge and radially in toward a negative point charge.
E =F/q

E=qE + qV × B

A charge that is moving relative to the source will experience part of the force as a magnetic field.

*The electric field intensity is the measure of the system of an electric field at any point . The electric field intensity between two points is the vector sum of all the electric field acting at that point .