15. The magnetic field B at a distance r from a long, straight conductor carrying a current / has a magnitude 4,1 B = B= 2r (c) (a) %3D B = (b) 2 %3D (d) None 16. Two parallel current attract each other by the force ( a ) /2r (b) uo II' /2 (c) Ho II' /4 r (d) None 17. Ampere's law states that the line integral of B around any closed path equals to (a) 2 6 B. dl = Ho Tenct (b) 4 6 B. dl = (c) B.dl = (d) None Ho lenct = Ho lencl 18. Magnetic field (B) due to a solenoid of circumference length of 2m is (a) uoNI/2 (b) NI2r (c) Zero (d) None 19. The magnetic susceptibility xm is defined (a) Km-1 (b) 2Km-1 (c) 6Km-1 (d) None 20. Which has the negative susceptibility (2) (a) Paramagnetic (b) Diamagnetic (c) Ferromagnetic (d) All of the above