Frequency Domain Analysis – 1 – 4

16. For a stable system :

(a) gain margin must be positive but phase margin can be positive or negative
(b) phase margin must be positive but gain margin can be positive or negative
(c) both gain margin and phase margin must be positive
(d)
 one of them must be zero

ANSWER

EXPLANATION

17. At the phase crossover frequency, ω =10 rad/s,│G(j ω)H(j ω) │= 15 dB. Its gain margin :

(a) 15 dB
(b) 0 dB
(c) -15 dB
(d) cannot be predicted

ANSWER

EXPLANATION

18. At the gain crossover frequency :

(a) │G G(jω)H(jω) │ = 0 dB
(b) │ G(jω)H(jω) │ = 1 dB
(c) │ G(jω)H(jω) │ = -20 dB
(d) 
│ G(jω)H(jω) │ = 20 dB

ANSWER

EXPLANATION

19. For the pole factor 1/(s+5), the corner frequency is :

(a) ω = 1/5
(b) ω = 5
(c) ω = -5
(d)
 ω = -1/5

ANSWER

EXPLANATION

20. For a second – order system, ωn = 8 and ξ= 0.5. The value of ωr in rad/s is :

(a) 4.657
(b) 5.657
(c) 6.657
(d) none of these

ANSWER

EXPLANATION

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