Question

If a Nyquist plot of G (jω) H (jω) for a closed loop system passes through (-2, j0) point in GH plane, what would be the value of gain margin of the system in dB?

(a) 0 dB

(b) 2.0201 dB

(c) 4 dB

(d) 6.0205 dB

This question was posed to me by my school teacher while I was bunking the class.

This intriguing question comes from Nyquist Stability Criterion topic in division Stability in Frequency Domain of Control Systems

Answer 1

Right option is (d) 6.0205 dB

The best I can explain: Gain Margin is calculated by taking inverse of the gain where the Nyquist plot cuts the real axis.