This set of Control Systems Multiple Choice Questions & Answers (MCQs) focuses on “Assessment of Relative Stability Using Nyquist Criterion”.

1. The system with the open loop transfer function G(s) H(s) =1/s(s^{^}2+s+1) has the gain margin of :

a) -6 dB

b) 0 dB

c) 3.5 dB

d) 6 dB

2. The phase angle of the system, G(s) =s+5/s^{2}+4s+9, varies between :

a) 0° and 90°

b) 0° and -90°

c) 0° and -180°

d) -90° and -180°

3. The phase margin (in degrees) of a system having the loop transfer function G(s) H(s)=2√3/s(s+1) is:

a) 45°

b) -30°

c) 60°

d) 30°

4. The polar plot of the transfer function G(s) = 10(s+1)/s+10 will be in the :

a) First quadrant

b) Second quadrant

c) Third quadrant

d) Fourth quadrant

5. Polar plots moving toward the imaginary axis makes the system:

a) Stable

b) Marginally stable

c) Conditionally stable

d) Unstable

6. Phase and gain margin are applicable to open and closed loop systems both.

a) True

b) False

7. As the polar plot moves toward the point (-1, 0) then the system becomes :

a) Stable

b) Marginally stable

c) Conditionally stable

d) Unstable

8. The concepts used to measure relative stability are:

a) Phase margin

b) Gain margin

c) Phase and Gain margin

d) Stable

9. Gain margin is:

a) It is a factor by which the system gain can be increased to drive it to the verge of instability

b) It is calculated at gain cross over frequency

c) It is calculated at phase cross over frequency

d) Both a and c

10. Phase margin is:

a) It is amount of additional phase lag at the gain cross over frequency required to bring the system to the verge of instability

b) It is always positive for stable feedback systems

c) It is calculated at gain cross over frequency

d) All of the mentioned