Consider an infinate current carrying wire along the z-axis. Let I be the current in the wire and suppose that flowing electrons produce this current. The wire has no net charge density because the density of positive ions is assumed to compensate the density of flowing electrons. Let the density of electrons per meter in the wire be p (phi). What is the typical velocity of the current electrons expressed in terms of p and I? velocity density and current in one equation... J=pv should be ok, since it is for a 3D region and we are talking about the density INSDIE a wire. Give the Lorentz Transformation that describes the transformation into the electrons rest frame hmmm, help? What is the density of electrons and ions in this frame? Is the wire also uncharged in the rest frame? density is always the least in the frame where charge is at rest. if it were uncharged wouldnt it mean that there is no current? my only other explanation is that is is uncharged because the electrons and ions cancel, but they dont, or else they would cancel in the normal frame as well... What is the total current in this frame? there is a current, but it doesnt take into account the electrons because they are at rest. how to find the current? the current cant be calculated by part (a) because it doesnt make a distinction between electrons and ions. could it be that the current is the same? Is there a frame conceivable in which the total current vanishes? in the in the normal frame, electrons are moving and ions are at rest. at a rest frame, electrons are at rest and ions are moving. so is there a frame where the ions and electrons cancel?