# Stability Theory – Exercise – 2

51. The parameter which is constant along the constant N circle is :

(a) frequency
(b) phase angle
(c) magnitude
(d) open-loop gain

Explanation
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52. If the s-plane contour encloses 2 zeros and 2 poles of q(s), the corresponding q(s) plane contour will encircle the origin of q(s) plane :

(a) twice in clockwise direction
(b) twice in counterclockwise direction
(c) zero times
(d) four times

Explanation
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53. The phase margin of a system is 40˚. The damping ratio of the system ξ is approximately :

(a) 0.04
(b) 0.4
(c) 4
(d) cannot be estimated

Explanation
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54. The damping ratio of a second-order system is 0.2. Its phase margin is approximately :

(a) 0.4˚
(b) 2˚
(c) 20˚
(d) 40˚

Explanation
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55. A polar plot crosses the real axis at (-1 + j0) point. The gain margin of the system is :

(a) -1˚
(b) 0˚
(c) -180˚
(d) +180˚