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.
What is the primary function of a feedback control system?
Answer: A
Feedback control systems work by comparing the desired output with actual output and reducing the error between them through corrective action.
Q.2Easy
The transfer function of a system is defined as the ratio of:
Answer: B
Transfer function G(s) = Y(s)/U(s) is the ratio of Laplace transforms of output to input assuming zero initial conditions.
Q.3Easy
Which of the following represents a first-order system?
Answer: B
A first-order system has only s¹ as the highest power in the denominator. G(s) = K/(τs + 1) is the standard first-order form.
Q.4Medium
What is the steady-state error for a unit step input to a Type 0 system?
Answer: C
For Type 0 system with unit step input, e_ss = 1/(1 + Kp) where Kp is the position error constant.
Q.5Easy
The characteristic equation of a system is s² + 4s + 3 = 0. The system is:
Answer: C
Roots are s = -1 and s = -3 (both negative). All poles are in the left half-plane, making the system stable.
Q.6Medium
What does the Routh-Hurwitz criterion determine?
Answer: B
Routh-Hurwitz criterion is used to determine the stability of a system by examining the characteristic equation coefficients without calculating poles.
Q.7Easy
In a bode plot, the magnitude is plotted on a scale of:
Answer: B
Bode plots use dB (20log₁₀|G(jω)|) for magnitude on a logarithmic scale and phase in degrees on a semi-log plot.
Q.8Medium
The gain margin of a system can be determined from the bode plot as:
Answer: C
Gain margin = 1/|G(jω)| at phase crossover frequency where phase = -180°. It indicates how much gain can be increased before instability.
Q.9Medium
For a second-order system with natural frequency ωn = 2 rad/s and damping ratio ζ = 0.5, the system is:
Answer: B
When ζ < 1 (0.5 < 1), the system is underdamped with oscillatory transient response.
Q.10Medium
The rise time of a second-order underdamped system decreases with:
Answer: A
Rise time tr ≈ (π - cos⁻¹(ζ))/(ωn√(1-ζ²)). It decreases with higher ωn and appropriate ζ value.
Q.11Medium
Which compensation technique is used to improve steady-state accuracy?
Answer: B
Lag compensation increases the system type or gain at low frequencies, improving steady-state accuracy without affecting stability significantly.
Q.12Medium
The Nyquist plot is a mapping of:
Answer: B
Nyquist plot maps the frequency response G(jω)H(jω) in the complex plane by varying ω from 0 to ∞.
Q.13Easy
For a system G(s) = 1/(s(s+2)), the number of poles at origin is:
Answer: B
The system has one pole at s=0, making it Type 1. The denominator has s¹ factor representing one integration.
Q.14Medium
The overshoot of a second-order system is independent of:
Answer: C
Overshoot = e^(-πζ/√(1-ζ²)) depends only on damping ratio ζ, not on ωn or system gain K.
Q.15Medium
Which of the following is a state-space representation advantage over transfer function?
Answer: B
State-space representation naturally handles MIMO systems, non-linear systems, and time-varying systems better than transfer functions.
Q.16Easy
The settling time of a control system is defined as the time taken to:
Answer: C
Settling time is the time required for the transient to decay and response to remain within 2% (or 5%) of the steady-state value.
Q.17Hard
For a system with open-loop transfer function G(s)H(s) = K/[s(s+1)(s+2)], the number of asymptotes in root locus is:
Answer: B
Number of asymptotes = n - m = 3 - 1 = 2, where n=3 (poles) and m=1 (zeros).
Q.18Hard
A proportional-integral (PI) controller transfer function is Gc(s) = Kp + Ki/s. Its effect is:
Answer: B
PI controller adds a pole at origin (integral term), increasing system type by 1 and eliminating steady-state error for step and ramp inputs.
Q.19Hard
The centroid of asymptotes in root locus is located at:
Answer: A
Centroid σ = (∑poles - ∑zeros)/(n-m), where n and m are number of poles and zeros respectively.
Q.20Hard
In phase-lead compensation, the zero is placed:
Answer: A
In lead compensation, zero is placed to the left of pole (closer to origin), providing phase lead to improve transient response and stability margin.
