40) The wattmeter reading of transformer on open circuit test is 900 W and on short circuit test at full load current is 1600 W. What will be the iron loss at half full load ?

41) The copper loss of the transformer during the maximum efficiency is 1000 watts, what will be the Iron loss ?

42) The efficiency of a transformer is at a maximum value, when the

43) Generally a transformer has the efficiency of

44) Results of a transformer with a rating of 15 kVA, 1100V/ 220V, 50Hz are obtained, while testing. Short circuit test power input = 510 watts. Open circuit test power input = 252 watts. What is the efficiency of the transformer at full load, 0.8 p.f.?