Multiple Choice Questions on Frequency Response Analysis

Multiple Choice Questions on Bode Plot, Nyquist Plot and Polar Plot

1. Pim pri S.N. Question Option A Option B Option C Option D
1
In frequency response, the resonance frequency is basically a measure of
_______ of response.
Speed Distance Angle Curvature
2
If a system is said to have a damping ξ = 0.5532 with the natu ral frequency
ω
n
= 2 rad/sec, what will be the value of resonant frequency (ω
r)?
1.2456 rad/s 1.7352 rad/s 2.3421 rad/s
3.66 rad/s
3
If the resonant peak is estimated to be '5', which among the f ollowing would
be the correct value of damping?
ξ = 0.3 ξ = 1 ξ = 3.2
ξ = 5.55
4
If the unity feedback system is given by the open loop transfer function G(s)
= ks
2
/ [(1 + 0.3s) (1+ 0.05s)], what would be the initial slope of magnitude
plot?
20 dB/decade 40 dB/decade 60 dB/decade
Unpredictable
5
If the constant 'k' is positive, then what would be its contrib ution on the
phase plot?
0° 45° 90°
180°
6
If the phase angle at gain crossover frequency is estimated to be -105°,
what will be the value of phase margin of the system?
23° 45° 60°
75°
7
At which frequency does the magnitude of the system becomes zero dB?
Resonant
frequency
Cut-off frequency
Gain crossover
frequency
Phase crossover
frequency
8
The frequency at which the phase of the system acquires ____ is known as
'Phase crossover frequency'.
90° -90° 180°
-180°
9
If a pole is located at origin, how does it get represented on the magnitude
plot?
-10 log (ω) dB -20 log (ω) dB -40 log (ω) dB
-60 log (ω) dB
10
Which unit is adopted for magnitude measurement in Bode plots?
DegreeDecimal Decibel Deviation
11
If the system is represented by G(s) H(s) = k (s+7) / s (s +3) (s + 2), what
would be its magnitude at ω = ∞?
0 ∞ 2/3
21
Max. Marks: 50Time: 04:30 am to 05:30 am
Pimpri Chinchwad Education Trust's
Pimpri Chinchwad College of Engineering & Research, R avet.
De
p
artment of Electronics & Telecommunication En
g
ineerin
g
SE Unit Test-II
Class: S.E. E&TCSubject: Control Systems ( Unit-IV)

2. 12
Consider the system represented by the equation given below. Wh at would
be the total phase value at ω = 0? 200/ [s3 (s + 3) (s + 6) (s + 10)] -90° -180° -270°
-360°
13
If the damping of the system becomes equal to zero, which cond ition of the
resonant frequency is likely to occur?
ω
r = ω
d
ω
r > ω
n
ω
r < ω
n
ω
r = ω
n
14
At which condition of 'ξ', resonant peak does not exist and its maximum
value is considered to be unity along with zero resonant freque ncy?
0 < ξ < 0.707 ξ > 0.707 ξ = 0
ξ = 1
15
If 'ξ' approaches to zero, the peak resonance would ________ Also be zero Be unity Tend to infinity
Become equal to
peak overshoot
16
How is the sinusoidal transfer function obtained from the syste m transfer
function in frequency domain?
Replacement of
'jω' by 's'
Replacement of
's' by 'ω'
Replacement of 's'
by 'jω'
Replacement of 'ω'
by 's'
17
Which plots in frequency domain represent the two separate plot s of
magnitude and phase against frequency in logarithmic value?
Polar plots Bode plots Nyquist plots
All of the above
18
Which of the following is the time domain method of determining stability
of a control system
Bode Plot
Nyquist Plot Polar Plot
Root Locus
Technique
19
On the Bode magnitude plot, the slope of the pole 1/(5 + jω)
2
is 20 dB/decade 40 dB/decade - 40 dB/decade -20 dB/decade
20
Phase Margin is used to specify _________
Frequency
Response
Absolute
Stability
Relative Stability Time Response
21
Which principle specifies the relationship between enclosure of poles &
zeros by s-plane contour and the encirclement of origin by q(s) plane
contour?
Argument Agreement Assessment
Assortment
22
If a Nyquist plot of G (jω) H (jω) for a closed loop system pas ses through (-2,
j0) point in GH plane, what would be the value of gain margin o f the system
in dB?
0 dB 2.0201 dB 4 dB
6.0205 dB
23
According to Nyquist stability criterion, where should be the position of all
zeros of q(s) corresponding to s-plane?
On left half At the center On right half
Random
24
For Nyquist contour, the size of radius is _______ 25 0 1
∞
25
In polar plots, what does each and every point represent w.r.t magnitude and
angle?
Scalar Vector Phasor
Differentiator

3. 26If the poles of a system lie on the imaginary axis, the system will be
Stable
Conditionally
Stable
Marginally Stable Unstable
27
The open-loop transfer function of a system is H(s)G(s) =
10/s(s + 2)(s + 5)
0
12 3
28 Which of the following is used for Nyquist Plot?
Characteristic
Equation
OLTF CLTF None of these
29 The Polar plot for G(S)H(S) = 10/s is ________
negative real
axis
postitive real axis negative jw axis postive jw axis
30 Zeros of 1+G(S)H(S) are __________ of the system
closed loop
p
oles
closed loop zeros open loop poles open loop zeros
31 The closed loop poles of G(S)H(S)=10/S(S+2) are___________ 0,-2 0, -1±j3 0,-5 0, -1±j2
32Resonant peak of a marginally stable system is0 infinity finite any of the above
33
In the Bode Plot of a unity feedback control system, the value of phase G(jw)
at the gain cross over frequency is -125 degree. The phase marg in of the
sytem is
125° 55° 180° 150°
34 The initial slope of the Bode plot gives an indication of
Type of the
s
y
ste
m
nature of the
s
y
stem time
system stability gain margin
35 At gain cross over frequency, magnitude of G(jw) H(jw) = ____ ___ dB 20 -20 -40 0
36 At phase cross over frequency angle of G(jw) H(jw) = ________ _
-90° -180° -270°
-360°
37 What is the angle contribution by two poles at origin in Bode Plots?
-90° -180° -270°
-360°
38
For gain crossover frequency < phase cross over frequency, the PM is ____
and system is _____
negative, Stable Positive, Stable negative, UnStable Positive, UnS table

4. 39
The system has ____ factor if slope of the magnitude plot chang es by -20
dB/dec at a particular frequency.
simple zero simple pole quadratic pole quadratic zero
40 The corner frequencies for G(S) H(S) = 30(1+0.2S)/ S(1+0.1S) are ______ 1,10,5 1,0.1,0.2 5,10 5,10,100
41 A system shows resonant peak = 2 then its damping ratio is 0.28 0.455 0.2588 0.5594
42 A System has Mr=2 and wr= 4 rad/sec then its wn = ____ rad/se c 4.296 9.246 6.294 2.694
43 _________ represents Nyquist Criterion N=P N-P=0 N+P=0 N=0
The Polar plot for positive frequencies is shown in the figure. Its GM= ____
dB
The type of the system whose polar plot is as show in figure is ________
46
For obtaining the frequency domain T.F., the variable S is repl aced by
jw w jw2 j
-9.542
4501 2 3
44
6.02
-6.02 9.542

5. 47
When a system is excited by purely sinusoidal input then ____ o f input and
output remains same.
Magnitude Phase angle frequency none of these
48
The resonant frequency is given by ____
(ω
n
) √(1‐2ζ²) (ω
n
) √(1‐4ζ²) (ω
n
) √(1‐1/ζ²) (ω
n
) √(1‐ζ²)
49
A second order under damped system has damping ratio of 0.3. Fi nd the 
phase margin of the system? 20° 3° 30° 60°
50
If the magnitude of G(jω)H(jω) at phase crossover frequency is  0.5. Find the 
gain margin of the given system?0.5 2 1 4