  Intense electromagnetic fields are created in the quark-gluon plasma by the
external ultra-relativistic valence charges. The time-evolution and the
strength of this field are strongly affected by the electrical conductivity of
the plasma. Yet, it has recently been observed that the effect of the magnetic
field on the plasma flow is small. We compute the effect of plasma flow on
magnetic field and demonstrate that it is less than 10\%. These observations
indicate that the plasma hydrodynamics and the dynamics of electromagnetic
field decouple. Thus, it is a very good approximation, on the one hand, to
study QGP in the background electromagnetic field generated by external sources
and, on the other hand, to investigate the dynamics of magnetic field in the
background plasma. We also argue that the wake induced by the magnetic field in
plasma is negligible.
