36. Two coils X and Y are placed in a circuit such that a current changes by 2 Amps in coil X and the magnetic flux change of 0.4 Wb occurs in coil Y. The mutual inductance of the coils is :
(A) 0.2 H
(B) 1.6 H
(C) 0.05 H
(D) 0.8 H
37. The coefficient of coupling between two tightly coupled coils wound on a magnetic core is :
(A) Zero
(B) 0.5
(C) 1
(D) 0.6
38. The efficiency ‘n’ of a 3-phase alternator is given by :
(A) 
(B) 
(C) 
(D) 
39. When a high resistive load is connected to a single-phase transformer at full load , its input power factor and load power factor are :
(A) high lagging p.f. & unity p.f. respectively
(B) low lagging p.f. & unity p.f. respectively
(C) unity p.f. & high lagging p.f. respectively
(D) unity p.f. & low lagging p.f. respectively
40. The core of power transformer is made up of :
(A) thin laminations with low resistivity
(B) thin laminations with high resistivity
(C) thick laminations with low resistivity
(D) thick laminations with high resistivity