Nyquist stability is determined by:

• A. Poles only
• B. Encirclements of (−1,0)
• C. Zeros only
• D. Bandwidth

Answer: (B)

Nyquist stability is determined by the number of encirclements of the point (-1,0) in the complex plane, which relates to the Nyquist criterion. This criterion is used to assess the stability of a control system based on its open-loop frequency response.

When analyzing a closed-loop system, if the Nyquist plot (a graphical representation of the frequency response) encircles the point (-1,0) in a specific way, it indicates whether the system will be stable or unstable. Specifically, the number of clockwise encirclements of the point (-1,0) corresponds to the number of poles of the closed-loop transfer function that lie in the right-half of the complex plane. By applying the Nyquist criterion, engineers can determine the stability of the system without the need to compute the exact poles and zeros of the transfer function.

The other aspects mentioned, like poles or zeros, are related to system dynamics but do not directly define stability as determined by the Nyquist criterion. Bandwidth refers to the frequency range over which the system operates effectively, but it is not a direct measure for stability in the same way that encirclements of (-1, 0) are. Thus, the correct answer focuses squarely on the significance