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.
The transfer function of an ideal derivative controller is:
Answer: A
A derivative controller has transfer function Gc(s) = Kd·s, where Kd is the derivative gain. It provides leading phase.
Q.122Easy
For a system G(s) = K(s+2)/[s(s+1)(s+3)], the number of asymptotes in root locus is:
Answer: B
Number of asymptotes = |poles - zeros| = |3 - 1| = 2. Three poles, one zero gives 2 asymptotes.
Q.123Easy
In digital control systems, the sampling theorem requires sampling frequency to be:
Answer: A
Nyquist sampling theorem: fs > 2·fmax to avoid aliasing. The sampling frequency must be at least twice the highest frequency component.
Q.124Easy
A second-order system has natural frequency ωn = 10 rad/s and damping ratio ζ = 0.5. The peak overshoot percentage is approximately:
Answer: A
Using the formula for peak overshoot: Mp = exp(-ζπ/√(1-ζ²)) × 100 = exp(-0.5π/√0.75) × 100 ≈ 16.3%. This is independent of ωn.
Q.125Easy
A PID controller Gc(s) = Kp + Ki/s + Kd·s is applied to a process. Which parameter adjustment would primarily reduce steady-state error without affecting transient response significantly?
Answer: B
The integral term (Ki) directly addresses steady-state error by accumulating past errors. Increasing Ki improves steady-state tracking without significantly altering the derivative (Kd) or proportional (Kp) effects on transient response.
Q.126Easy
Which of the following is a unidirectional device in power electronics?
Answer: D
Both diodes and thyristors are unidirectional devices that conduct current in only one direction. MOSFETs are bidirectional.
Q.127Easy
The forward voltage drop across a silicon diode at room temperature is approximately:
Answer: B
Silicon diodes have a typical forward voltage drop of 0.6-0.7 V at room temperature. Germanium diodes have ~0.3 V.
Q.128Easy
Which device is used to convert DC to AC power?
Answer: B
An inverter converts DC power to AC power. Rectifiers do the opposite (AC to DC). Choppers convert DC to DC.
Q.129Easy
The peak inverse voltage (PIV) rating of a diode is important to prevent:
Answer: B
PIV rating defines the maximum reverse voltage a diode can withstand without breaking down. Exceeding this causes reverse breakdown and device failure.
Q.130Easy
In MOSFET, the gate-source voltage at which current starts to flow is called:
Answer: B
Threshold voltage (Vth) is the gate-source voltage required to create an inversion layer and allow current flow in MOSFET.
Q.131Easy
In a buck converter, the output voltage is always:
Answer: A
A buck converter steps down the input voltage. The output voltage Vo = D×Vin where D is the duty cycle (0 < D < 1), making output always less than input.
Q.132Easy
The maximum frequency of a thyristor is typically limited by:
Answer: B
Turn-off time (tq) determines the minimum period required between successive gate pulses, thus limiting the maximum operating frequency of thyristors.
Q.133Easy
A PWM inverter with sinusoidal modulation produces output voltage with:
Answer: B
Sinusoidal PWM produces a voltage waveform containing the fundamental frequency plus high-frequency harmonics that can be filtered out.
Q.134Easy
The presence of freewheeling diode in a DC motor drive is essential because it:
Answer: A
The motor inductance tends to maintain current flow. The freewheeling diode provides a path for this current when the main switch is off, preventing voltage spikes.
Q.135Easy
In a boost converter operating in continuous conduction mode (CCM), if the duty cycle is 0.5 and input voltage is 12V, what is the output voltage?
Answer: A
For a boost converter, Vo/Vin = 1/(1-D). With D=0.5, Vo = 12/(1-0.5) = 24V
Q.136Easy
Which of the following devices is a unidirectional switch in power electronics?
Answer: A
A diode conducts only in one direction (forward bias), making it a unidirectional switch
Q.137Easy
In a half-bridge inverter, what is the minimum number of switches required to generate AC output from DC source?
Answer: A
A half-bridge inverter requires 2 switches (typically with 2 diodes) to generate AC output from a DC source
Q.138Easy
What is the primary purpose of a freewheeling diode in a buck converter?
Answer: B
The freewheeling diode provides a continuous path for the inductor current during the switch OFF period, preventing voltage spikes
Q.139Easy
In a three-phase full-bridge inverter, the total number of thyristors required is:
Answer: C
A three-phase full-bridge inverter requires 6 thyristors (2 per phase) to generate three-phase AC output
Q.140Easy
In a buck-boost converter, the polarity of output voltage compared to input is:
Answer: B
A buck-boost converter produces an output voltage of opposite polarity to the input voltage, with magnitude |Vo| = Vin × D/(1-D)
