Electrical Engineering questions for GATE, PSU recruitment and SSC JE draw from network theory, electrical machines, power systems, control systems, measurements and instrumentation, analog and digital electronics, and electromagnetic fields. Numerical answers include the formula used and the unit at each stage, which is where marks are commonly lost even when the approach is correct.
In a 3-phase squirrel cage induction motor, which parameter can be increased to improve the starting torque?
Answer: C
Starting torque in an induction motor is proportional to rotor current and rotor resistance. Increasing rotor resistance improves starting torque at the cost of full-load efficiency.
Q.42Medium
The slot leakage reactance in an induction motor depends on:
Answer: B
Slot leakage reactance is determined by the magnetic flux confined within the stator and rotor slots, hence depends on dimensions of both stator and rotor slots.
Q.43Medium
In a DC generator, armature reaction causes:
Answer: C
Armature reaction in DC generators creates a demagnetizing effect and shifts the neutral plane forward (in direction of rotation), both effects occurring simultaneously.
Q.44Medium
The power factor of a transformer at no-load is low because:
Answer: B
At no-load, the transformer draws mainly magnetizing current which lags the applied voltage by approximately 90°, resulting in low power factor (typically 0.1-0.2).
Q.45Medium
Which of the following losses in an induction motor is proportional to slip?
Answer: C
Rotor copper loss = sP_gap, where s is slip and P_gap is the air gap power. It is directly proportional to slip.
Q.46Medium
In a separately excited DC motor, if flux is reduced to half while keeping the supply voltage constant, the armature current will:
Answer: C
Back EMF = KΦω. When Φ is halved, back EMF reduces, so armature current (Ia = (V - Eb)/Ra) increases approximately to double for the same load.
Q.47Medium
The regulation of a DC shunt generator is poor because:
Answer: B
In a DC shunt generator, as load increases, armature current increases, causing armature reaction that demagnetizes the field, reducing terminal voltage significantly.
Q.48Medium
In a 3-phase synchronous generator, the pitch factor (or coil span factor) accounts for:
Answer: B
Pitch factor (Kp) accounts for the reduction in EMF when the coil span is less than the pole pitch (full pitch), representing incomplete flux linkage.
Q.49Medium
In a transformer connected to a load with lagging power factor, the secondary current will:
Answer: B
If the load has lagging power factor, the secondary current lags the secondary voltage. The phase relationship between primary and secondary depends on the load power factor.
Q.50Medium
A 3-phase squirrel cage induction motor is running at 960 rpm when connected to a 50 Hz supply. If the supply frequency is suddenly changed to 60 Hz, what will be the approximate new speed of the motor, assuming the slip remains constant?
Answer: A
Synchronous speed Ns = 120f/P. When frequency changes from 50 Hz to 60 Hz with constant slip, new speed will be proportional to frequency. New speed = 960 × (5060) = 1152 rpm. This is because slip s = (Ns - N)/Ns remains approximately constant for the same load.
