# Integral of product of infintesimal volume

1. Sep 28, 2013

### vijaypandey93

I'm following the book ''introduction to electrodynamics by D.J. Griffiths''. As he has written that the formula ''integral of product of infintesimal volume with the square of electric field'' gives us the energy contained in a charge configuration that is always positive because we're encountering square.He has justified it by saying that it even considers the fabrication of charges and as we know the fabrication of point charge involves infinte energy.But why do i get a definite value when i calculate the energy of a charge configuration like spherical or cylindrical,rather if i'm following his argument correctly then in spherical,this formula should take into account of fabrication of all the charges and that's certainly infinite.what's that in his argument that i'm not getting?Please help!

2. Sep 28, 2013

### Simon Bridge

3. Sep 28, 2013

### vijaypandey93

okay but what'd we get if we calculate the energy due to equal and opposite charges?should it be positive or negative?according to the formula statrd above,it'll always be positive.and using the formula [k(q1)(q2)]/r,it's negative.can you please justify how?

4. Sep 28, 2013

### Simon Bridge

Last edited by a moderator: Sep 25, 2014