85. Coil diameter d = 20 cm can be rotated about a vertical axis coinciding with one of the diameter of the coil. Revolution installed in the plane of the magnetic meridian, and let him on the current of I = 10 A. Find mechanical moment M, which must be applied to a coil, to keep him in the starting position. (Horizontal component Bz of the magnetic induction field of the Earth taken equal to 20 mT).

Detailed solution. Decorated in Microsoft Word 2003. (Target decided to use formula editor)