[" 2.A long straight wire of radius a carries a steady current "I" ."],[" The current is unifornly distributed over its cross-section."],[" The ratio of the magnetic fields "B" and "B" ,at radial distances "],[(a)/(2)" and "2a" respectively,from the axis of the wire is "],[[" (a) "(1)/(4),(2y)/(1/2)quad (1)/(2)b=(11)/(21)=(2a)/(9/2)],[" (c) "1,," (4) "4quad (B)/(B')=(4)/(1)]]