- #1
insynC
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Homework Statement
If the current density is time independent and divergence free, show that the Maxwell Equations separate into independent equations for [tex]\vec{E}[/tex] and [tex]\vec{B}[/tex].
Homework Equations
Maxwell's equations
The Attempt at a Solution
The only Maxwell equation with [tex]\vec{j}[/tex] in it is the Maxwell-Ampere law, so that seems like the right place to start. By taking the partial derivative with respect to time of this equation and using the fact [tex]\vec{j}[/tex] is time independent, Faraday's Law and Gauss' Law for [tex]\vec{B}[/tex] I can get a wave equation for [tex]\vec{B}[/tex].
What is confusing me is how to use the fact [tex]\vec{j}[/tex] is divergence free. If I take the divergence of the Maxwell-Ampere equation I get:
∇⋅∇x[tex]\vec{B}[/tex] = εµ (∂∇⋅[tex]\vec{E}[/tex]/∂t) + µ ∇[tex]\vec{j}[/tex]
The LHS = 0 (vector identity), ∇[tex]\vec{j}[/tex] = 0 as given, and then using Gauss' Law for [tex]\vec{E}[/tex] I simply get:
(∂ρ)/(∂t) = 0
But this isn't surprising as the equation of charge conservation would have given me this anyway. How do I get the equation for [tex]\vec{E}[/tex]? Thanks.