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### Electric Charges and Coulumb's Law

- Charges are of two types
(a) positive charge
(b) negative charge

- like charges repel each other and unlike charges attract each other.

-Properties of charge
1. quantisation :- q=ne where n=0,۫, ........ and e is charge of an electron.
3. conservation :- total charge of an isolated system is constant

-Coulumb's law
The mutual electrostatic force between the charges q1 and q2 seperated by a distance r is given by
Force on the charge q1
F1=Kq1q2r12/r2
where r12 is the unit vector in the direction from q2 to q1
similarly force on charge q2 is
F2=Kq1q2r21/r2
where r21 is the unit vector in the direction from q1 to q2
F1+F2=0
If there are more than 2 charges present in the system then force acting on any charges is vector sum of the couloumb force from each of the other charges.This is called principle of superposition
Mathematically
Let q1,q2,q3......qn
charges are present in the system
Then Force on charge q1
F=Kq1q2r12/r122+Kq1q3r13/r132+Kq1q4r14/r142....Kq1qnr1n/r1n2

Similarly for the other charges...

Important point to note on this
1. The force with which two charges interact is not changed by the presence of the other charges
2. Net force on any charge
F=F1+F1+F1+F1....