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

(a) frequency

(b) phase angle

(c) magnitude

(d) open-loop gain

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

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

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˚

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˚

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