For a specified input voltage and frequency, if the equivalent radius of the core of a transformer is reduced by half, the factor by which the number of turns in the primary should change to maintain the same no load current is

Assuming an ideal transformer, The Thevenin's equivalent voltage and impedance as seen from the terminals x and y for the circuit in figure are

A single phase, 50 kVA, 1000 V/100 V two winding transformer is connected as an autotransformer as shown in the figure. The kVA rating of the autotransformer is _________.

A single-phase transformer has no-load loss of 64 W, as obtained from an open circuit test. When a short-circuit test is performed on it with 90% of the rated currents flowing in its both LV and HV windings, he measured loss is 81 W. The transformer has maximum efficiency when operated at