Consider a system of

*n*stationary charges*q*_{1},*q*_{2},*q*_{3}, ...,*q**n*in vacuum. Force on any charge due to a number of other charges is the vector sum of all the forces on that charge due to the other charges, taken one at a time. The individual forces are unaffected due to the presence of other charges. This is**termed as the****principle****of superposition****.****C**onsider a system of three charges

*q*

_{1},

*q*

_{2 }and

*q*

_{3}

_{,}as shown in

**Fig.**

*The force on one charge, say*

*q*1, due to two other charges

*q*2,

*q*3 can therefore be obtained by performing a vector addition of the forces due to each one of these charges. Thus, if the force on

*q*

_{1 }due to

*q*

_{2}is denoted by

**F**12,

**F**12 is given by

*q*

_{1}due to

*q*

_{3}, denoted by

**F**13, is given by

*q*

_{1}due to

*q*

_{3}

_{,}even though other charge

*q*2 is present.

Thus the total force

**F**1 on*q*_{1}due to the two charges*q*_{2 }and*q*_{3}is given as
The above calculation of
force can be generalized to a system of charges more than three, as shown in below
Fig.

The principle of
superposition says that in a system of charges

*q*1,*q*2,*..., q**n**,*the force on*q*1 due to*q*2 is the same as given by Coulomb’s law, i.e., it is unaffected by the presence of the other charges*q*3,*q*4,*..., q**n*.
The total force

**F**1 on the charge*q*1, due to all other charges, is then given by the vector sum of the forces**F**12,**F**13, ...,**F**1*n*:
The vector sum is obtained as
usual by the parallelogram law of addition of vectors. All of electrostatics is
basically a consequence of Coulomb’s law and the superposition principle.

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**Some of these questions which may be asked in your Board Examination 2012-2013**

**Q1: When a plastic comb is passed through dry hair, what type of charge is acquire by comb?**

Q2: Does motion of a body affect its charge?

Q3: What is the origin of frictional forces?

**Answer these questions in comment box and help your friends**

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