# Quiz: Electrical Engineering 24 May 2021

Quiz: Electrical Engineering
Exam: DFCCIL
Topic: Control system

Each question carries 1 mark.
Negative marking: 1/4 mark
Time: 10 Minute

Q1. The type-2 system has ……………at the origin?
(a) No pole
(b) Net pole
(c) Simple pole
(d) Two poles

Q2. With feedback……………reduces?
(a) nSystem stability
(b) System gain
(c) Both a and b
(d) None of the above

Q3. If the gain margin of a system in decibels is negative, the system is
(a) Stable
(b) Marginally stable
(c) Unstable
(d) Could be stable or unstable or marginally stable

Q4. Consider a network function H(s)= (2(s+3))/((s+2)(s+4)). What is the steady state response due to step input?
(a) ½
(b) ¾
(c) 2
9d) 1

Q5. A system with gain margin close to unity or a phase margin close to zero is
(a) relative stable
(b) oscillatory
(c) stable
(d) highly stable

Q6. What is the value of the damping ratio of a second order system when the value of
the resonant peak is unity?
(a) √2
(b) 1
(c) 1/√2
(d) 0

Q7. What are the gain and phase angle of a system having the transfer function
G(s) = (s + 1) at a frequency of 1 rad/s?
(a) 0.41 and 0°
(b) 1.41 and 45°
(c) 1.41 and -45°
(d) 2.41 and 90°

Q8. The response c(t) of a system is described by the differential equation
(d^2 c(t))/(dt^2 ) + 4(dc(t))/dt + 5c(t) = 0
The system response is
(a) undamped
(b) underdamped
(c) critically damped
(d) oscillatory

Q9. System is said to be marginally stable, if
(a) Gain crossover frequency > Phase crossover frequency
(b) Gain crossover frequency = Phase crossover frequency
(c) Gain crossover frequency < Phase crossover frequency
(d) Gain crossover frequency ≠ Phase crossover frequency

Q10. The polar plot of a Transfer function passes through the critical point (-1, 0). The
gain margin is
(a) 0 dB
(b) -1 dB
(c) 1 dB
(d) infinity

SOLUTIONS
S1. Ans.(d)
Sol. Type of system=number of poles at origin.

S2. Ans.(b)
Sol. With positive feedback, system gain reduces.

S3. Ans.(c)
Sol. For system to be stable, Gain Margin in dB and Phase Margin in degree must be +ve.
NOTE: For unstable system the signs of gain margin and phase margin are always different or they can both be negative.

S4. Ans.(b)
Sol. steady state response=lim┬(s→0)⁡〖sC(s)=〗 lim┬(s→0)⁡= s×(2(s+3))/((s+2)(s+4))×1/s=3/4

S5. Ans.(b)
Sol. System with Unity Gain margin and ‘0’ Phase angle is Oscillatory in nature.

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