# Retarded Fields

1. Apr 9, 2012

### PLuz

While studying Jackson J.D. "Classical Electrodynamics" 3rd edition in chapter 14.1, page 663 he does something that I don't quite get it.

He gets an expression for the retarded potencial and says that he can use the integral form of the 4-potencial to easily get an expression for the Maxwell tensor. Then he explains that he must do the derivative and that derivative must apply to both the $\theta$ and $\delta$ function. All that I agree.

Then he applies the first derivation to the $\theta$ function and explains that it constrains the $\delta$ function and get $\delta(-R^2)$ so that term is only important when $R=0$. I still agree.
But then he discards it saying it makes no contribution if one excludes the point $R=0$...Why can he discard that point?

Thank you

Last edited: Apr 10, 2012