M A current i, at Li produces an open circuit voltage u,at L ○L32U y21=M21U2= dv21=M21 t M A current i, at L2 produces an 十 open circuit voltage U,atLIs L Y12=M12L2 0,dv12 M d t 12 dt The mutual inductance: M12-M2IM(H) The coefficient of coupling: k=M ≤1 (i2→DC.U,U2=0) 1三A current i1 at L1 produces an open circuit voltage at L2 .  2 21 21 1  = M i A current i2 at L2 produces an open circuit voltage at L1 . 1 12 12 2  = M i The mutual inductance: M12=M21=M(H) The coefficient of coupling: 1 1 2 =  L L M k ( . , 0) If i 1, i 2  DC 1  2 = − +  2 1 i 2 i − +  1 L1 L2 M L1 L2 M dt di M dt d 1 21 21 2 = =   dt di M dt d 2 12 12 1 = =  