PHYSICS · Multi-part · Fermi University Physics · Plasma Physics · Fluid and magnetohydrodynamic description · Laboratory, industrial and space plasmas
Plasma Physics, Ch Magnetohydrodynamics: Ohm's law for a moving plasma, frozen flux and magnetic pressure
Problem
Someone argues: "In an ideal, perfectly conducting plasma the resistive term in Ohm's law vanishes, so ηj=0. But Ohm's law is just E=ηj, so E=0 everywhere. A perfectly conducting solar wind blowing past a spacecraft therefore carries no electric field at all, and the interplanetary field lines cannot be dragged along by the flow because there is nothing left to drag them."
((a)) Find the error in this argument.
((b)) The solar wind blows at U=400kms−1 across a field B=5nT, with U and B perpendicular. Calculate the electric field a spacecraft at rest actually measures.