Electrostatics - calculation of electric field intensity

[logearav]

electrostatics --- calculation of electric field intensity

Homework Statement

My aim is to calculate electric field intensity at a point P where the test charge q_o is kept which is at a distance r from the source charge q is kept.

Homework Equations

Why it has mentioned limit q_o tends to zero is mentioned in coulomb's law in my attached image?

The Attempt at a Solution

 

[ehild]

We define the electric field around a charged body by putting a test charge qo at a certain distance and measure the electric force acting on it. But the additional charge will modify the field. In case when the "fixed charge" is distributed on a metal sphere, even the charge distribution can change. That is why we need to use a very small test charge. The influence of the test charge is less and less as qo tends to zero and we take the electric field strength as the force acting on the test charge at that limit. If we apply this definition, the field around a charged metal sphere is the same as that of a point charge placed in the centre.

ehild

 

[logearav]

Thanks for the reply ehild

 

[ashishsinghal]

It tends to zero so that its magnitude is such that it does not affect the field by polarizing or attracting other charges.

 

[logearav]

Thanks ashishsinghal for the clarification