Calculate the skin-depth of a plane electromagnetic wave of frequency 50 hz in copper sheet wire of conductivity 5.8 10' (per ohm-m) and relative magnetic permeability b. in wires with diameter much greater than the skin-depth, ac currents locate near to the surface. how thick can a copper wire carrying 50hz currents usefully be, assuming the amplitude at the centre of the wire is double that calculated from plane-wave attenuation and skin depth? [this "doubling" arises because the field can penetrate from two directions rather than from just one]. define your criterion for "useful". c. calculate the skin-depth of a plane electromagnetic wave of frequency 60 hz in amorphous cobalt magnetic shielding wire of conductivity 7*10 (per ohm-m) and relative magnetic permeability 1,000,000 d. how thick would the walls of a shielded roomm made out of copper have to be to reduce the internal powerline noise field to 1 part per million of its external value? e. how thick would the walls need to be using amorphous cobalt shielding?