# Derivation of Lienard-Wiechart

1. May 10, 2009

### snoopies622

Can anyone point me to a derivation of the Lienard-Wiechart potential formulas? I assume that they can be derived from Maxwell's equations alone.

Thanks.

2. May 10, 2009

### Staff: Mentor

3. May 11, 2009

### snoopies622

That is very helpful, thank you.

A follow-up question, if I may:

What makes

$$( \frac {\phi }{c} , A^x , A^y , A^z )$$

a four-vector? That is, why is applying a Lorentz transformation to it vaild? Is the electric potential somehow the time-component of the magnetic potential? Is

$$\vec B = \nabla \times \vec A$$

still valid if A is four dimensional? Is the curl of a four-dimensional vector field even defined?

4. May 11, 2009

### dx

The analog of that equation is Fαβ = ∂αAβ - ∂βAα. The thing on the right is the four dimensional curl. The thing on the left is the Farady tensor.

5. May 11, 2009

### clem

$$(\phi,{\vec A})$$ is chosen to be a 4-vector in a LT so that the continuity equation
$$\partial_\mu A^\mu=0$$ will hold in any LT so charge conservation will hold in any Loentz system.
They are no longer called the electric and magnetic potential, but just the 4-vector potential.

6. May 11, 2009

### snoopies622

OK, good. Thanks.

I'm sorry - could you re-word this? I'm not sure I get your meaning.