Automatic Control Systems MCQs

1. In a closed-loop control system, the transfer function of the feedback path is:

A. Unity
B. Zero
C. Greater than one
D. Less than one
Answer: A

2. The steady-state error of a control system can be reduced by:

A. Increasing the gain of the system
B. Decreasing the gain of the system
C. Changing the reference input
D. None of the above
Answer: A

3. The transfer function of a system is given by G(s) = 1 / (s+1). The type of the system is:

A. Type 0
B. Type 1
C. Type 2
D. Type 3
Answer: A

4. Which of the following is not a type of controller?

A. Proportional
B. Integral
C. Derivative
D. Recursive
Answer: D

5. The phase margin of a system indicates:

A. System stability
B. System bandwidth
C. System gain
D. System damping
Answer: A

6. Nyquist stability criterion is based on:

A. Polar plot
B. Bode plot
C. Root locus plot
D. Frequency response plot
Answer: A

7. A lead compensator is used to:

A. Increase the gain of the system
B. Decrease the gain of the system
C. Increase the stability of the system
D. Decrease the stability of the system
Answer: C

8. The transfer function of a PI controller in Laplace domain is:

A. Kps\frac{K_p}{s}sKp​​
B. KpK_pKp​ / $s$
C. Kp(1+1s)K_p \left(1 + \frac{1}{s}\right)Kp​(1+s1​)
D. Kps\frac{K_p}{s}sKp​​

Answer: C

9. The characteristic equation of a closed-loop control system is given by:

A. $1+G(s)H(s)=0$
B. $1-G(s)H(s)=0$
C. $G(s)H(s)=1$
D. $G(s)H(s)=0$
Answer: B

10. Which of the following is a non-linear control system?

A. PID control system
B. Phase-locked loop
C. Adaptive control system
D. Bang-bang control system
Answer: D

11. The transfer function G(s)=Ks(s+1)(s+2)G(s) = \frac{K}{s(s+1)(s+2)}G(s)=s(s+1)(s+2)K​ represents a system of order:

A. 1
B. 2
C. 3
D. 4
Answer: C

12. The process of finding the transfer function of a system from its differential equations is called:

A. Fourier transformation
B. Laplace transformation
C. Z-transform
D. State-space representation
Answer: B

13. Root locus plot gives information about:

A. Magnitude response
B. Phase response
C. Pole locations
D. Stability
Answer: D

14. Which of the following methods is used for time response analysis of control systems?

A. Bode plot
B. Nyquist plot
C. Routh-Hurwitz criterion
D. Step response
Answer: D

15. In a control system, the steady-state error is zero for a ramp input, if the system type is:

A. Type 0
B. Type 1
C. Type 2
D. Type 3
Answer: B

16. The transfer function of a lag compensator is generally of the form:

A. Ks+a1s+1\frac{K}{s+a} \frac{1}{s+1}s+aK​s+11​
B. K(s+1)s+a\frac{K(s+1)}{s+a}s+aK(s+1)​
C. K(s−1)s+1\frac{K(s-1)}{s+1}s+1K(s−1)​
D. K(s+1)s−1\frac{K(s+1)}{s-1}s−1K(s+1)​
Answer: B

17. A system is said to be unstable if:

A. All poles lie in the left half of the s-plane
B. All poles lie in the right half of the s-plane
C. It has no poles
D. It has only one pole
Answer: B

18. The transfer function G(s)=10s(s+1)(s+2)G(s) = \frac{10}{s(s+1)(s+2)}G(s)=s(s+1)(s+2)10​ has poles at:

A. s = -1, s = -2
B. s = 1, s = 2
C. s = -1, s = 2
D. s = 1, s = -2
Answer: A

19. The steady-state error for a step input in a unity feedback control system with a proportional controller is:

A. Infinite
B. Zero
C. Unity
D. One
Answer: B

20. A PI controller is used to eliminate:

A. Steady-state error
B. Transient response
C. Oscillations
D. None of the above
Answer: A

21. A phase-lead compensator is used to:

A. Increase the stability of the system
B. Decrease the stability of the system
C. Increase the gain of the system
D. Decrease the gain of the system
Answer: A

22. The frequency at which the gain of the system is unity is known as:

A. Crossover frequency
B. Bandwidth frequency
C. Resonant frequency
D. Phase margin frequency
Answer: A

23. The gain margin of a system is the reciprocal of:

A. Phase margin
B. Crossover frequency
C. Resonant frequency
D. Gain crossover frequency
Answer: A

24. The transfer function G(s)=Ks(s+1)G(s) = \frac{K}{s(s+1)}G(s)=s(s+1)K​ represents a system of order:

A. 1
B. 2
C. 3
D. 4
Answer: B

25. The root locus technique is used to determine:

A. Steady-state error
B. Transient response
C. Stability of the system
D. Frequency response
Answer: C

26. The Bode plot consists of:

A. Magnitude plot only
B. Phase plot only
C. Both magnitude and phase plots
D. None of the above
Answer: C

27. The damping ratio of a system is given by:

A. ζωn\frac{\zeta}{\omega_n}ωn​ζ​
B. ωnζ\frac{\omega_n}{\zeta}ζωn​​
C. ωn2ζ\frac{\omega_n^2}{\zeta}ζωn2​​
D. ζωn2\frac{\zeta}{\omega_n^2}ωn2​ζ​
Answer: B

28. Which of the following is a disadvantage of feedback control systems?

A. Reduced sensitivity to parameter variations
B. Improved stability
C. Increased complexity
D. Reduced steady-state error
Answer: C

29. The steady-state error of a system depends on:

A. Proportional gain only
B. Integral gain only
C. Derivative gain only
D. Proportional, integral, and derivative gains
Answer: D

30. The transfer function G(s)=1s(s+1)G(s) = \frac{1}{s(s+1)}G(s)=s(s+1)1​ represents a:

A. Type 0 system
B. Type 1 system
C. Type 2 system
D. Type 3 system
Answer: B

31. The dominant pole of a system is:

A. The pole closest to the imaginary axis
B. The pole farthest from the imaginary axis
C. The pole with the highest magnitude
D. The pole with the lowest magnitude
Answer: A

32. A derivative controller is not widely used in practice because it:

A. Increases stability
B. Increases noise sensitivity
C. Reduces transient response
D. Improves steady-state error
Answer: B

33. The transfer function G(s)=Ks(s2+2s+2)G(s) = \frac{K}{s(s^2 + 2s + 2)}G(s)=s(s2+2s+2)K​ has poles at:

A. s = 0, s = -1 ± j
B. s = 0, s = -1 ± j
C. s = 1, s = -1 ± j
D. s = 1, s = -1 ± j
Answer: D

34. The primary purpose of a compensator in a control system is to:

A. Reduce bandwidth
B. Decrease system gain
C. Improve stability
D. Increase transient response
Answer: C

35. Which of the following is not a time domain specification of a control system?

A. Rise time
B. Overshoot
C. Damping ratio
D. Gain margin
Answer: D

36. A phase-locked loop (PLL) is commonly used in:

A. Analog signal processing
B. Digital signal processing
C. Power electronics
D. None of the above
Answer: B

37. A system is marginally stable if:

A. All poles lie on the imaginary axis
B. All poles lie on the real axis
C. The number of poles equals the number of zeros
D. The number of poles exceeds the number of zeros
Answer: A

38. The effect of derivative action in a PID controller is to:

A. Reduce steady-state error
B. Improve transient response
C. Increase stability
D. Decrease overshoot
Answer: B

39. The transfer function G(s)=K(s+1)s(s2+1)G(s) = \frac{K(s+1)}{s(s^2 + 1)}G(s)=s(s2+1)K(s+1)​ has poles at:

A. s = 0, s = ±j
B. s = 0, s = ±j
C. s = 1, s = ±j
D. s = 1, s = ±j
Answer: B

40. In control system design, the term “root locus” refers to the locus of:

A. Poles of the closed-loop system as a parameter varies
B. Zeros of the open-loop system as a parameter varies
C. Poles of the open-loop system as a parameter varies
D. Zeros of the closed-loop system as a parameter varies
Answer: A

41. The transfer function G(s)=Ks2(s+1)G(s) = \frac{K}{s^2(s+1)}G(s)=s2(s+1)K​ represents a system of order:

A. 1
B. 2
C. 3
D. 4
Answer: C

42. The bandwidth of a control system is defined as the frequency at which the:

A. Phase margin is zero
B. Gain margin is zero
C. Phase crossover frequency occurs
D. Gain crossover frequency occurs
Answer: D

43. The process of adjusting the parameters of a controller to improve system performance is called:

A. Tuning
B. Modulation
C. Simulation
D. Evaluation
Answer: A

44. The transfer function G(s)=10s(s+2)G(s) = \frac{10}{s(s+2)}G(s)=s(s+2)10​ has a pole at:

A. s = 0, s = -2
B. s = 1, s = 2
C. s = -1, s = 2
D. s = -1, s = -2
Answer: A

45. The transfer function G(s)=Ks(s+1)(s+2)G(s) = \frac{K}{s(s+1)(s+2)}G(s)=s(s+1)(s+2)K​ has a zero at:

A. s = 0
B. s = -1
C. s = -2
D. There are no zeros
Answer: A

46. The stability of a control system is determined by the:

A. Magnitude of the open-loop transfer function
B. Phase of the open-loop transfer function
C. Location of poles in the s-plane
D. Location of zeros in the s-plane
Answer: C

47. A lead compensator is used to improve:

A. Steady-state accuracy
B. Transient response
C. Frequency response
D. All of the above
Answer: B

48. The transfer function G(s)=Ks(s+1)G(s) = \frac{K}{s(s+1)}G(s)=s(s+1)K​ has a zero at:

A. s = 0
B. s = -1
C. There are no zeros
D. Cannot be determined from the given information
Answer: A

49. The transfer function G(s)=Ks(s+2)G(s) = \frac{K}{s(s+2)}G(s)=s(s+2)K​ represents a system of order:

A. 1
B. 2
C. 3
D. 4
Answer: B

50. A system is said to be critically damped when:

A. The damping ratio is 1
B. The damping ratio is less than 1
C. The damping ratio is greater than 1
D. The damping ratio is negative
Answer: A

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