Please answer these 3 questions..

​QC-16. A long, thick straight conductor of radius R carries current I uniformly distributed in its cross section area. The ratio of energy density of the magnetic field at distance R/2 from surface inside the conductor and outside the conductor is :

            (A) 1 :16                           (B) 1: 1                    (C) 1 : 4                     (D) 9/16
                                                                                                                                [15 JPI 20061]

QC-17. Two long parallel wires are at a distance 2d apart. they carry steady equal currents flowing out of the plane of the paper, as shown. The variation of the magnetic field B along XX' is given by
                                                                                                                                 [JEE 2000 [Scr.) 2/105]
                
 
QC-18. An infinitely long conductor PQR is bent to form a right angle as shown. A current 1 flows through PQR. The magnetic field due to this current at the point M is H₁. Now, another infinitely long straight conductor QS is connected at Q so that the current in PQ remaining unchanged. The magnetic field at M is now H₂. The ratio H₁/H₂ is given by ​                             
                                                                                                                                                                                                                                                                                    [JEE 2000 (S cr,).3/105] [16JP 20176] 
                                    

       (A) 1/2                             (B) 1                              (C) 2/3                          (D) 2