Synopsis of Electrical Engineering

Important Multiple Choice Questions on Electrical Machines 1.        Can a 50Hz transformer be used for a 25Hz if the input voltage is maintained constant at the rated value corresponding to 50Hz? a)       Yes. Since the voltage is constant, current levels will not change. b)       No. Flux will be doubled which will drive the core excessive saturation. c)        No. Owing to decreased reactance of transformer, input current will be doubled at load. d)       Yes. At constant voltage, insulation will not be overstressed. 2.        In a transformer, if the iron losses and copper losses are 40.5 kW and 50 kW respectively, then at what fraction of load will be the efficiency be maximum? a)       0.8 b)       0.57 c)        0.7 d)       0.9 3.        If the frequency of input voltage of the transformer is increased keeping the magnitude of voltage unchanged, then a)       Both the hysteresis and eddy current losses in the core will increase. b)       Hysteresis l

Important multiple choice questions on Electrical Machines 1.        To eliminate the single phasing torque in an ac servomotor, the rotor must have a)       Both high resistance and reactance. b)        High resistance. c)        High reactance. d)       Large air-gap 2.        If a single-winding single-phase motor is running in a particular direction a)       Both the rotating fields (rotating in opposite directions) have the same strength. b)       Forward rotating field is slightly stronger than the backward field. c)        Forward rotating field is much stronger than the backward field. d)       Backward field is stronger than the forward field. 3.        A single-winding single phase motor has a)       Low starting torque b)       Zero starting torque c)        High starting torque d)       Starting torque equal to full-load torque 4.        A single phase stator winding when excited with ac voltage produces a)       A single rotating field r