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10 Question-answer on transformer 1.        If the number of turns in primary and secondary coil is increased to two times each, the mutual inductance (a)     Become 4 time (b)    Become 2 time (c)     Become 1/4 time (d)    Remains unchanged. Ans: ( a) 2.        A transformer is used to light 140 W, 24 V lamp from 240 V a.c. mains. The current in the main is 0.7 A. the efficiency of transformer is nearest to (a)     90% (b)    80% (c)     70% (d)    60% Ans: ( b) 3.        In a step down transformer, use of 120 V line, provides a pot. Diff. of 2400 V. if the primary coil has 75 turns, number of turns in secondary coil is: (a)     150 (b)    1500 (c)     1200 (d)    1575 Ans: (b) 4.      ...