# Electrostatics - calculation of electric field intensity

1. Jun 24, 2011

### logearav

electrostatics --- calculation of electric field intensity

1. The problem statement, all variables and given/known data
My aim is to calculate electric field intensity at a point P where the test charge qo is kept which is at a distance r from the source charge q is kept.

2. Relevant equations

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

3. The attempt at a solution
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

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2. Jun 24, 2011

### ehild

Re: electrostatics --- calculation of electric field intensity

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

3. Jun 26, 2011

### logearav

Re: electrostatics --- calculation of electric field intensity

4. Jun 26, 2011

### ashishsinghal

Re: electrostatics --- calculation of electric field intensity

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

5. Jul 2, 2011

### logearav

Re: electrostatics --- calculation of electric field intensity

Thanks ashishsinghal for the clarification