1121. An ideal transformer does not change :
A. Voltage
B. Power *
C. Current
D. None of these
1122. For an ideal transformer the windings should have :
A. Most extreme obstruction on essential side and least opposition on auxiliary side
B. least obstruction on essential side and most extreme opposition on auxiliary side
C. Equivalent obstruction on essential and optional side
D. No Ohmic resistance on either sides *
1123. The core flux in transformer depends mainly on:
A. Supply voltage
B. Supply voltage and frequency *
C. Supply voltage frequency and load
D. None of them
1124. A transformer steps up the voltage by a factor 100 . The ratio of current in the primary to that into the secondary is :
A. 1
B. 100 *
C. 10
D. None
1125. If the applied voltage to transformer primary is increased by keeping the V ratio fixed. Then the magnetizing current and the core loss will respectively :
A. Decrease and remain the same
B. Increase and decrease
C. Both remain the same
D. Remain the same and increase *
1126. If the applied voltage of a certain transformer is increased by 50% and the frequency is reduced to 50% (assuming that the magnetic circuit remains unsaturated ) the maximum core flux density will:
A. Change to three times the original value *
B. Change to 1.5 times the first value
C. change to 0.5 times the original value
D. Remain the same as the original value
1127. If the supply frequency of a transformer is increased keeping the supply voltage constant then :
A. The current’s magnetizing and core loss components will both decrease *
B. The current’s magnetizing and core loss components will both increase
C. The current’s magnetizing and core loss components will both decrease
D. The current’s magnetizing and core loss components will both decrease
1128. The low voltage winding of a 400/230 v single phase 50 Hz transformer is to be connected to a 25 Hz SUPPLY. In order to keep the magnetising current at the same level in both the case the voltage at 25 Hz should be :
A. 230 v
B. 460 V
C. 115 V *
D. 65 V
1129. At 220 volts, 40 Hz, a single-phase transformer rated for 220/240 V. 50 Hz operates without load. This recurrence activity at appraised voltage brings about which one of the accompanying :
A. An increase in both the eddy-current loss and the hysteresis loss
B. An decrease in both the eddy-current loss and the hysteresis loss
C. An increase in both the eddy-current loss and the hysteresis loss
D. An increase in both the hysteresis loss and no change in the eddy-current loss *
1130. A 50 Hz transformer having equivalent hysteresis and vortex current misfortunes at evaluated excitation is worked at 45 Hz AT 90% of its appraised voltage. Contrasted with evaluated working point the center misfortunes under this condition :
A. Reduce by 10%
B. Reduce by 19%
C. Reduce by 14.5% *
D. Remains unchanged