Maxwell equation

$$ \nabla . \vec{E} = \frac{\rho}{\epsilon_0}$$

$$ \nabla . \vec{B} = 0$$

$$ \nabla \times \vec{E} = -\frac{\partial \vec{B}}{\partial t}$$

$$ \nabla \times \vec{B} = \mu_0 \vec{J}$$