Question { BSNL, 5790 }

. A superconductor is a
a.) A material showing perfect conductivity and Meissner
effect below a critical temperature
b.) A conductor having zero resistance
c.) A perfect conductor with highest di-magnetic susceptibility
d.) A perfect conductor which becomes resistance when the
current density through it exceeds a critical value

Answer

obviously it is a.

superconductivity was first described by H W KAMMERLING ONNES...
now this guy stated that certain elements exhibit zero
resistances at low temp called as critical temperature....

also there is this meisner's effect where the magnetc field
fail to exist within that particular line..