Step 1: Apply the Routh-Hurwitz criterion.
The Routh-Hurwitz criterion is applied to determine the stability of the system. We form the Routh array using the coefficients of the characteristic equation. For stability, the number of sign changes in the first column determines the value of \(K_c\) that will keep the system stable.
Step 2: Conclusion.
Using the Routh test, we find that the correct value of \(K_c\) that keeps the system stable is (C) 13.5.
Consider the unity-negative-feedback system shown in Figure (i) below, where gain \( K \geq 0 \). The root locus of this system is shown in Figure (ii) below.
For what value(s) of \( K \) will the system in Figure (i) have a pole at \( -1 + j1 \)?

Consider a message signal \( m(t) \) which is bandlimited to \( [-W, W] \), where \( W \) is in Hz. Consider the following two modulation schemes for the message signal:
• Double sideband-suppressed carrier (DSB-SC): \[ f_{DSB}(t) = A_c m(t) \cos(2\pi f_c t) \] • Amplitude modulation (AM): \[ f_{AM}(t) = A_c \left( 1 + \mu m(t) \right) \cos(2\pi f_c t) \] Here, \( A_c \) and \( f_c \) are the amplitude and frequency (in Hz) of the carrier, respectively. In the case of AM, \( \mu \) denotes the modulation index. Consider the following statements:
(i) An envelope detector can be used for demodulation in the DSB-SC scheme if \( m(t)>0 \) for all \( t \).
(ii) An envelope detector can be used for demodulation in the AM scheme only if \( m(t)>0 \) for all \( t \).
Which of the following options is/are correct?