# Multiple Choice Question (MCQ) of Control Systems page-10

97. Cut off frequency is the frequency at which magnitude of closed loop frequency response is

a) 1 db below its zero frequency
b) 2 db below its zero frequency
c) 3 db below its zero frequency
d) 4 db below its zero frequency

Ans: (c)

98. In Nyquist criterion roots of the characteristic equation are given by

a) Zeros of open loop transfer function
b) Zeros of closed loop transfer function
c) Poles of closed loop transfer function
d) Poles of open loop transfer function

Ans: (c)

99. For all frequencies, a unit circle in the Nyquist plot transformer into

a) Db line of amplitude plot in Bode diagram
b) 1 db line of amplitude plot in Bode diagram
c) Either (a) and (b)
d) None of these

Ans: (c)

100. Transfer founction, when the bode diagram is plotted should be of the form

a) (1+T)
b) (1+S)
c) (Ts)
d) (1+Ts)

Ans: (d)

101. For relative stability of the system which of the following is sufficient?

a) Gain margin
b) Phase margin
c) Both (a) and (b)
d) None of these

Ans: (c)

102. Slope in Bode plot is expressed as

b) – 6 db/octave
c) – 7 db/octave
d) – 8 db/octave

Ans: (b)

103. Polar plots for+ve and –ve frequencies

a) Are always symmetrical
b) Can never be symmetrical
c) May be symmetrical
d) None of these

Ans: (a)

104. Gain margin of a first or second order system is

a) Zero
b) 100
c) 1
d) Infinity

Ans: (d)

105. Frequency range over which response of the system is within acceptable limits is called system

a) Modulation frequency
b) Demodulation frequency
c) Carrier frequency
d) Band width

Ans: (d)

106. By adding a pole at s = 0, Nyquist plot of the system will

a) Shift 90° clockwise
b) Shift 90° anticlockwise
c) Shift 180°
d) Not change at all

Ans: (a)

107. A complex-conjugate pair of poles near the jw axis will produce a

a) High oscillatory mode of transient response
b) Steady state mode of response
c) Sinusoidal mode of response
d) None of these

Ans: (a)

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