Correct Answer : Option (C) : 8
Explanation :
The given open-loop feedback control system is: G(s)H(s) = 1 / [(s + 1) ^3]
The phase angle for the cross-over frequency can be calculated by:
-3 tan-1 ω=-180°
We get the value of ω=√3
Now, the gain margin is the magnitude of the transfer function, as shown below:
= 1 / |G(s)H(s)| = |(j√3+13|
= 8
