The root locus technique is used to determine:

 Q1. The main function of a control system is to:

A) Amplify signals
B) Reduce errors
C) Maintain the desired output with minimal error
D) Increase speed of response

✅ Answer: C) Maintain the desired output with minimal error
Explanation:
A control system continuously monitors and adjusts its output to match a desired reference input. The aim is to minimize the error between the reference and the output.

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Q2. In an open-loop control system:
A) Output is fed back to input
B) There is no feedback path
C) The system has self-correcting properties
D) It is always stable

✅ Answer: B) There is no feedback path
Explanation:
An open-loop system acts based only on input commands without comparing the output to the desired value. Example: electric toaster.

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Q3. Which of the following is an example of a closed-loop system?
A) Washing machine
B) Traffic light control
C) Automatic voltage regulator
D) Bread toaster

✅ Answer: C) Automatic voltage regulator
Explanation:
A closed-loop (feedback) system senses the output voltage and adjusts excitation to maintain the desired voltage.

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Q4. The transfer function of a system is defined as the ratio of:
A) Input to output
B) Output to input under zero initial conditions
C) Feedback to forward path
D) Gain to error

✅ Answer: B) Output to input under zero initial conditions
Explanation:
Transfer function $G(s) = \frac{Output(s)}{Input(s)}$ when all initial conditions are zero. It characterizes the dynamic behavior of a system in the frequency domain.

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Q5. The feedback in a control system helps to:
A) Increase gain
B) Reduce sensitivity to parameter variations
C) Reduce accuracy
D) Make system open loop

✅ Answer: B) Reduce sensitivity to parameter variations
Explanation:
Feedback stabilizes system performance, reduces sensitivity to disturbances, and improves accuracy and bandwidth.

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Q6. Which one of the following systems is inherently unstable?
A) Open loop
B) Closed loop
C) Positive feedback
D) Negative feedback

✅ Answer: C) Positive feedback
Explanation:
Positive feedback increases the overall gain and can cause the output to grow uncontrollably, leading to instability.

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Q7. The term “steady-state error” refers to:
A) Error that occurs at zero input
B) Error that remains after transients die out
C) Error during initial condition
D) Error due to noise

✅ Answer: B) Error that remains after transients die out
Explanation:
Steady-state error measures the difference between desired and actual output once the system reaches steady conditions.

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Q8. In time domain analysis, which of the following represents the system performance?
A) Nyquist plot
B) Root locus
C) Step response
D) Bode plot

✅ Answer: C) Step response
Explanation:
Step response is a key time-domain method to study transient and steady-state performance of control systems.

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Q9. The Laplace transform is used in control systems to:
A) Simplify differential equations into algebraic form
B) Measure steady-state error
C) Plot frequency response
D) Determine time constants directly

✅ Answer: A) Simplify differential equations into algebraic form
Explanation:
Laplace transform converts time-domain differential equations into algebraic equations in the ‘s’ domain, simplifying system analysis.

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Q10. The root locus technique is used to determine:
A) Time response of the system
B) Stability and location of system poles
C) Frequency response
D) Steady-state error

✅ Answer: B) Stability and location of system poles
Explanation:
Root locus shows how the roots of the characteristic equation vary with system parameters (usually gain), helping analyze stability.