Stability Analysis from Polar Plot

Q. The polar plot of a type-1, 3-pole, open-loop system is shown in figure below. The closed loop system is

1. always stable.
2. marginally stable.
3. unstable with one pole on the right half s-plane.
4. unstable with two pole on the right half s-plane.

Q. The polar diagram of a conditionally stable system for open loop gain $K=1$ is shown in the figure. Theopen loop transfer function of the system is known to be stable. The closed loop system is stable for

1. $K<5and\frac{1}{2}<K<\frac{1}{8}$
2. $K<\frac{1}{8}and\frac{1}{2}<K<5$
3. $K<\frac{1}{8}and5<K$
4. $K<\frac{1}{8}andK<5$

Q.
The magnitude Bode plot of a network is shown in the figure

The maximum phase angle ${\varphi }_m$ and the corresponding gain $G_m$ respectively, are

1. $-{30}^{\circ }and1.73dB$
2. $-{30}^{\circ }and4.77dB$
3. $+{30}^{\circ }and4.77dB$
4. $+{30}^{\circ }and1.73dB$