71. Among the following which nucleus has negative quadrupole moment? (1) H (2) Li6 (3) B10 (4) 92U235 72. The surface energy term in semi- empirical mass formula is proportional to nth power of mass number A. Here n is (1) (3) +/ 1 (2) 4 (4) 3 73. Choose incorrect statement: (1) Nuclear forces are charge independent. (2) Nuclear force are spin and angular momentum dependent. (3) Nuclear forces depend upon the velocity of the nucleons. (4) Nuclear forces are central forces. 74. The magnetic field of amplitude B, and angular frequency o) is established in a Betatron of radius R. The maximum energy of electron with velocity v in it is (1) RB0 (2) evRBo (3) veRB0 (4) veRB 75. What will be the electric field intensity at the surface of anode in a proportional counter if radius of central wire is 1 mm, inner radius of the cylinder is 1.0 cm and voltage applied to anode is 1000 V ? 106 Vm-1 (1) (2) 1.44 x 106 Vm-1 (3) 0.43 x 106 Vm-1 (4) 1.44 x 103 Vm-1