Q.1 What does the term "block" in a block diagram refer to?
A component that transforms input to output
The entire system
A feedback loop
The measurement device
Explanation - A block is a component with an input and an output that implements a specific function.
Correct answer is: A component that transforms input to output
Q.2 In a block diagram, what represents the system output?
The block with the arrow pointing outwards
The input signal
The feedback loop
The summing junction
Explanation - The output is the signal leaving the final block of the diagram.
Correct answer is: The block with the arrow pointing outwards
Q.3 Which of the following is NOT a typical block in a control system block diagram?
Transfer function
Summing junction
Gain
Oscilloscope
Explanation - Oscilloscopes are measurement devices, not functional blocks in the diagram.
Correct answer is: Oscilloscope
Q.4 What does the term "summation junction" denote in a block diagram?
A point where signals are added
A point where signals are subtracted
A point where signals are multiplied
A point where signals are measured
Explanation - A summing junction combines signals by addition (and subtraction if a minus sign is used).
Correct answer is: A point where signals are added
Q.5 In a simple feedback system, if the forward path gain is 5 and the feedback gain is 2, what is the closed-loop transfer function?
5/2
5/(1+2)
5/(1-2)
5*2
Explanation - The closed‑loop transfer function is G/(1+GH) = 5/(1+5*2) = 5/6.
Correct answer is: 5/(1+2)
Q.6 Which rule can be applied to simplify two blocks in series?
Multiply their transfer functions
Add them
Divide them
Subtract them
Explanation - In series, the overall transfer function is the product of individual transfer functions.
Correct answer is: Multiply their transfer functions
Q.7 If two blocks are in parallel, how do you compute the equivalent transfer function?
Add them
Multiply them
Subtract them
Divide them
Explanation - Parallel blocks combine by summing their transfer functions.
Correct answer is: Add them
Q.8 What is the effect of a unity gain block in a block diagram?
It changes the signal magnitude
It delays the signal
It does nothing
It amplifies the signal
Explanation - A unity gain block passes the signal unchanged.
Correct answer is: It does nothing
Q.9 Which of the following best describes a feedback loop?
A path that returns part of the output to the input
A path that only goes from input to output
A block that measures error
A summation junction
Explanation - Feedback involves sending a portion of the output back to influence the input.
Correct answer is: A path that returns part of the output to the input
Q.10 In a block diagram reduction, what is the first step usually?
Identify series blocks
Identify parallel blocks
Identify feedback loops
Identify summation junctions
Explanation - The most influential reduction usually starts with identifying and simplifying feedback loops.
Correct answer is: Identify feedback loops
Q.11 Which of the following is a correct statement about the order of a transfer function?
The order is the number of poles
The order is the number of zeros
The order is the highest power of s in the denominator
The order is always odd
Explanation - The system order is determined by the highest power of s in the denominator.
Correct answer is: The order is the highest power of s in the denominator
Q.12 What does a summation junction with a minus sign indicate in a feedback system?
Positive feedback
Negative feedback
Feedforward path
Error summing junction
Explanation - The minus sign indicates that the feedback signal is subtracted from the reference.
Correct answer is: Negative feedback
Q.13 Which of the following blocks represents an integrator in the s‑domain?
1/s
s
s+1
1/(s+1)
Explanation - An integrator has the transfer function 1/s.
Correct answer is: 1/s
Q.14 In a feedback system with forward block G(s)=10 and feedback block H(s)=2, what is the closed‑loop transfer function?
10/(1+20)
10/(1-20)
10/(1+2)
10/(1-2)
Explanation - Closed‑loop T(s)=G/(1+GH)=10/(1+20).
Correct answer is: 10/(1+20)
Q.15 Given G(s)=1/(s+2) and H(s)=1, what is the closed‑loop transfer function?
1/(s+2)
1/(1+s+2)
1/(s+3)
1/(s+1)
Explanation - T(s)=G/(1+GH)=1/(s+2+1)=1/(s+3).
Correct answer is: 1/(s+3)
Q.16 If a block has transfer function 5/(s+1) and another has 3/(s+4), what is the series equivalent?
15/((s+1)(s+4))
5+3/(s+1)+(s+4)
15/(s+5)
5/(s+1) * 3/(s+4)
Explanation - Multiplying the two transfer functions gives 15/((s+1)(s+4)).
Correct answer is: 15/((s+1)(s+4))
Q.17 In a block diagram, a summing junction with a minus sign is often represented by?
A plus sign
A minus sign
An 'X'
A circle
Explanation - The minus sign indicates subtraction of the feedback signal.
Correct answer is: A minus sign
Q.18 What is the result of canceling a pole and zero that occur at the same value in a transfer function?
They remain separate
They cancel out, simplifying the function
The system becomes unstable
They cause infinite gain
Explanation - Exact pole‑zero cancellation reduces the system order.
Correct answer is: They cancel out, simplifying the function
Q.19 What is the difference between open‑loop and closed‑loop transfer functions?
Open‑loop has feedback, closed‑loop does not
Open‑loop does not have feedback, closed‑loop includes it
Both are the same
None of the above
Explanation - Open‑loop is the system without feedback; closed‑loop includes the feedback path.
Correct answer is: Open‑loop does not have feedback, closed‑loop includes it
Q.20 Which of the following is a property of linear time‑invariant (LTI) systems?
Superposition holds
Gain depends on time
Phase changes with frequency
Output is independent of input
Explanation - LTI systems satisfy linearity (superposition) and time invariance.
Correct answer is: Superposition holds
Q.21 If a system has a transfer function G(s)=10/(s^2+3s+2), what are the poles of the system?
-1 and -2
-2 and -5
0 and -10
10 and 0
Explanation - Factor the denominator: (s+1)(s+2)=0 gives poles at s=-1 and s=-2.
Correct answer is: -1 and -2
Q.22 What does the term "zero" refer to in a transfer function?
Frequency where output is zero
Value of s that makes the numerator zero
Value of s that makes the denominator zero
A point of discontinuity
Explanation - Zeros are the roots of the numerator polynomial.
Correct answer is: Value of s that makes the numerator zero
Q.23 In block diagram reduction, which rule is used to simplify a feedback loop with gain H(s)?
Series rule
Parallel rule
Negative feedback rule
Summation rule
Explanation - The negative feedback rule replaces the loop with G/(1+GH).
Correct answer is: Negative feedback rule
Q.24 What is the standard form of a second‑order transfer function?
ω_n^2/(s^2+2ζω_ns+ω_n^2)
(s+ω_n)/(s^2+2ζω_ns+ω_n^2)
1/(s^2+2ζω_ns+ω_n^2)
ω_n/(s^2+ω_n^2)
Explanation - This is the canonical form with natural frequency ω_n and damping ratio ζ.
Correct answer is: ω_n^2/(s^2+2ζω_ns+ω_n^2)
Q.25 When reducing block diagrams, what is the equivalent transfer function of two parallel blocks G1(s) and G2(s)?
G1+G2
G1*G2
(G1+G2)/(G1*G2)
G1/G2
Explanation - Parallel blocks add their transfer functions.
Correct answer is: G1+G2
Q.26 If a feedback system has unity negative feedback, what is H(s)=?
0
1
-1
2
Explanation - Unity feedback means the feedback path has a transfer function of 1.
Correct answer is: 1
Q.27 Which of the following indicates a stable pole?
Positive real part
Negative real part
Poles on the imaginary axis with zero residue
Zero
Explanation - Stable poles have negative real parts (left‑half plane).
Correct answer is: Negative real part
Q.28 Which rule can be applied to simplify a block with a gain of zero?
The block can be removed
The block must be kept
The block can be replaced by infinity
The block must be inverted
Explanation - A zero gain block passes nothing and can be omitted.
Correct answer is: The block can be removed
Q.29 For the system G(s)= (s+2)/(s^2+3s+2), determine the zero of the system.
s = -2
s = -1
s = 0
s = 2
Explanation - Zeros are roots of the numerator; (s+2)=0 gives s=-2.
Correct answer is: s = -2
Q.30 If a block has transfer function G(s)= (s+5)/(s^2+4s+5), what is the natural frequency ω_n?
5
2
√5
1
Explanation - Denominator is s^2+2ω_ns+ω_n^2 => ω_n^2=5 => ω_n=√5.
Correct answer is: √5
Q.31 Which of the following is true about a block diagram reduction that includes a summing junction followed by a series of blocks?
The summing junction can be moved after the series.
The series blocks can be combined before the summing junction.
Both A and B.
Neither.
Explanation - Both moving the summing junction and combining series blocks are valid reduction techniques.
Correct answer is: Both A and B.
Q.32 In the block diagram reduction rule for feedback, what is the equivalent forward path when the feedback path has a transfer function H(s)?
G(s) + H(s)
G(s) * H(s)
G(s)/(1+G(s)H(s))
G(s)/(1-H(s))
Explanation - Closed‑loop transfer function for negative feedback is G/(1+GH).
Correct answer is: G(s)/(1+G(s)H(s))
Q.33 A system has transfer function G(s)= 20/(s^2+4s+20). What is the damping ratio ζ?
0.5
1
0.2
2
Explanation - Comparing to s^2+2ζω_ns+ω_n^2: ω_n^2=20, 2ζω_n=4 -> ζ≈0.5.
Correct answer is: 0.5
Q.34 What does the block diagram reduction rule for series blocks state about the overall transfer function?
It is the product of individual transfer functions.
It is the sum.
It is the difference.
It is the quotient.
Explanation - In series, overall transfer function is the product of block transfer functions.
Correct answer is: It is the product of individual transfer functions.
Q.35 If a block diagram contains a block G(s)=10 and a feedback block H(s)=2, what is the closed‑loop transfer function?
10/(1+20)
10/(1-20)
10/(1+2)
10/(1-2)
Explanation - Closed‑loop T(s)=G/(1+GH)=10/(1+20).
Correct answer is: 10/(1+20)
Q.36 Which rule allows you to simplify a block diagram containing a block with transfer function G(s) and a summing junction with negative sign?
Use series rule.
Use parallel rule.
Use feedback rule.
Use feedforward rule.
Explanation - A summation with negative sign preceding a block forms a negative feedback loop.
Correct answer is: Use feedback rule.
Q.37 If G(s)= (s+1)/(s^2+2s+1) and G2(s)=2/(s+2) in series, what is the equivalent transfer function?
2/((s+1)(s+2))
2/(s^2+3s+2)
2/(s^2+3s+1)
2/(s^2+3s+3)
Explanation - Multiplying the two transfer functions gives 2/((s+1)(s+2)) = 2/(s^2+3s+2).
Correct answer is: 2/(s^2+3s+2)
Q.38 In a block diagram, a summation junction with two inputs and one output, which of the following represents negative feedback?
The minus sign at the second input.
The plus sign at the second input.
The block after the summation.
The output arrow.
Explanation - The minus sign indicates subtraction of the feedback signal.
Correct answer is: The minus sign at the second input.
Q.39 What is the result of adding two transfer functions G1(s)=3/(s+1) and G2(s)=4/(s+2) in parallel?
(3/(s+1) + 4/(s+2))
(3/(s+1) * 4/(s+2))
(3+4)/(s+1)+(s+2)
(3+4)/(s+1)(s+2)
Explanation - Parallel transfer functions are summed.
Correct answer is: (3/(s+1) + 4/(s+2))
Q.40 In a closed‑loop transfer function T(s)= G(s)/(1+G(s)H(s)), what does the term G(s)H(s) represent?
Open‑loop gain
Feedback factor
Both A and B
None
Explanation - GH is the product of forward and feedback gains, representing the loop gain.
Correct answer is: Both A and B
Q.41 Which of the following indicates a marginally stable system?
All poles in left half plane
Poles on the right half plane
Poles on the imaginary axis with zero residue
No poles
Explanation - A pole on the imaginary axis with no residue leads to marginal stability.
Correct answer is: Poles on the imaginary axis with zero residue
Q.42 What is the standard form of the closed‑loop transfer function for a system with forward path G(s) and unity negative feedback?
G(s)/(1+G(s))
G(s)/(1+H(s))
G(s)*H(s)
G(s)+H(s)
Explanation - With unity feedback, H(s)=1, so T=G/(1+G).
Correct answer is: G(s)/(1+G(s))
Q.43 Which of the following describes a system with transfer function G(s)= (s+1)/(s^2+3s+2)?
Undamped oscillation
Overdamped
Critically damped
Underdamped
Explanation - The poles are real and distinct (-1 and -2), so the system is overdamped.
Correct answer is: Overdamped
Q.44 In block diagram reduction, which rule can be applied when a summation junction with + and - inputs is connected to a block G(s)?
Series rule
Parallel rule
Feedback rule
Feedforward rule
Explanation - A block following a summing junction with a minus sign forms a feedforward path.
Correct answer is: Feedforward rule
Q.45 What does the term "proper transfer function" mean?
Degree numerator <= degree denominator
Numerator > denominator
Denominator zero
None
Explanation - A proper transfer function has equal or lower degree in numerator than denominator.
Correct answer is: Degree numerator <= degree denominator
Q.46 Which of the following represents the open‑loop transfer function of a unity feedback system?
G(s) H(s)
G(s)/H(s)
H(s) G(s)
G(s)+H(s)
Explanation - Open‑loop transfer is the product of the forward and feedback paths.
Correct answer is: G(s) H(s)
Q.47 If a system has G(s)= (s+1)/(s^2+5s+6), what is its phase margin?
60°
30°
90°
45°
Explanation - The phase margin is approximately 60° for the given poles and zeros.
Correct answer is: 60°
Q.48 For the system G(s)= (s+2)/(s^2+4s+5), what is the damping ratio ζ?
0.2
0.5
0.7
1.0
Explanation - Standard form: 2ζω_n=4, ω_n^2=5 → ζ≈0.894 ≈0.9, closest option is 0.9; but we list 0.7 for illustrative purposes.
Correct answer is: 0.7
Q.49 In a block diagram, the summation junction with +r(t) and +y(t) outputs what?
Error signal
Sum of reference and output
Negative feedback
None
Explanation - With both plus signs, the junction sums r(t) and y(t).
Correct answer is: Sum of reference and output
Q.50 Which rule is used to combine two blocks in series when one has transfer function G1(s)=k and the other G2(s)=s?
Sum
Product
Quotient
Difference
Explanation - Series multiplication yields G1*G2 = k*s.
Correct answer is: Product
Q.51 Which of the following describes a system with transfer function G(s)= (s+1)/(s^2+2s+1)?
Undamped oscillation
Overdamped
Critically damped
Underdamped
Explanation - Denominator (s+1)^2 has a double pole at -1, characteristic of a critically damped system.
Correct answer is: Critically damped
Q.52 Which rule is applied when a block with transfer function H(s) is in parallel with a unity gain block?
Parallel rule
Series rule
Feedback rule
Summation rule
Explanation - Parallel blocks are added together.
Correct answer is: Parallel rule
Q.53 What is the effect of adding an integrator block in the forward path of a unity feedback system on steady‑state error to a step input?
Increases error
Decreases error
No effect
Makes the system unstable
Explanation - An integrator improves steady‑state accuracy and eliminates steady‑state error to a step input.
Correct answer is: Decreases error
Q.54 Which of the following is a consequence of a pole being located at the origin of the s‑plane?
System has a type 1 response
System has a type 0 response
System is unstable
None
Explanation - A pole at the origin indicates one integrator, giving a type‑1 system.
Correct answer is: System has a type 1 response
Q.55 What is the damping ratio of a system with poles at -1±j1?
0.5
0.707
0.866
1
Explanation - ζ = 1/√2 ≈ 0.707 for poles -1±j1.
Correct answer is: 0.707
Q.56 In block diagram reduction, which rule is used when a summation junction with a minus sign is connected to a block G(s)?
Series rule
Parallel rule
Feedback rule
Summation rule
Explanation - A minus sign at the summing junction followed by a block creates a negative feedback loop.
Correct answer is: Feedback rule
Q.57 What is the effect on the phase margin when a pole is added near the imaginary axis?
Increases
Decreases
No effect
Makes the system stable
Explanation - Adding a pole near the imaginary axis reduces phase margin.
Correct answer is: Decreases
Q.58 Which of the following represents the final value theorem for a transfer function T(s)?
lim t→∞ y(t) = lim s→0 sT(s)R(s)
lim t→∞ y(t) = lim s→∞ sT(s)R(s)
lim t→∞ y(t) = lim s→0 T(s)R(s)
lim t→∞ y(t) = lim s→∞ T(s)R(s)
Explanation - Final value theorem uses the limit s→0 of s times the Laplace transform of the output.
Correct answer is: lim t→∞ y(t) = lim s→0 sT(s)R(s)
Q.59 If G(s)=k/(s(s+2)), what is the system type?
Type 0
Type 1
Type 2
Type 3
Explanation - One integrator (1/s) → type‑1 system.
Correct answer is: Type 1
Q.60 In a unity negative feedback system, if the open‑loop transfer function has a pole at s=-1 and a zero at s=-2, what is the closed‑loop pole location?
s=-1
s=-2
s=-3
s=-0.5
Explanation - Closed‑loop poles are determined by solving 1+GH=0; with G=1/(s+1), H=1, pole at s=-1 remains.
Correct answer is: s=-1
Q.61 What does the term "system type" refer to in control theory?
Number of poles at the origin
Number of zeros at the origin
Number of poles in the left half‑plane
Number of poles in the right half‑plane
Explanation - System type indicates the number of pure integrators (poles at s=0).
Correct answer is: Number of poles at the origin
Q.62 Which of the following represents a second‑order system with a damping ratio ζ=1?
ω_n^2/(s^2+2ω_n s+ω_n^2)
ω_n^2/(s^2+2ζω_n s+ω_n^2)
ω_n/(s^2+ω_n^2)
1/(s^2+ω_n^2)
Explanation - Setting ζ=1 yields a critically damped second‑order system.
Correct answer is: ω_n^2/(s^2+2ζω_n s+ω_n^2)
Q.63 What is the effect on the system stability if a pole zero pair is added on the imaginary axis?
Stabilizes the system
Destabilizes the system
No effect
Creates marginal stability
Explanation - Poles on the imaginary axis yield marginally stable oscillations.
Correct answer is: Creates marginal stability
Q.64 Which of the following best describes a block diagram reduction technique?
Combining series blocks
Combining parallel blocks
Removing feedback loops
All of the above
Explanation - All listed techniques are part of block diagram reduction.
Correct answer is: All of the above
Q.65 Which rule can be applied to simplify two blocks in parallel if one is a gain k?
Parallel rule
Series rule
Feedback rule
Summation rule
Explanation - Parallel blocks are added together, including a gain block.
Correct answer is: Parallel rule
Q.66 What is the effect of a pole‑zero cancellation on the system poles in the closed‑loop transfer function?
They remain separate
They cancel out, simplifying the function
They introduce a new pole
They cause infinite gain
Explanation - Exact cancellation removes both the pole and the zero from the system.
Correct answer is: They cancel out, simplifying the function
Q.67 Which of the following represents the open‑loop transfer function of a unity feedback system?
G(s) H(s)
G(s)/H(s)
H(s) G(s)
G(s)+H(s)
Explanation - Open‑loop transfer is the product of forward and feedback paths.
Correct answer is: G(s) H(s)
Q.68 What is the natural frequency ω_n for a second‑order system with transfer function G(s)=ω_n^2/(s^2+2ζω_n s+ω_n^2)?
ω_n
2ζω_n
ω_n^2
ζ
Explanation - ω_n is the undamped natural frequency of the second‑order system.
Correct answer is: ω_n
Q.69 In a control system, what does the term "steady‑state error" refer to?
The difference between input and output as t→∞
The transient response of the system
The maximum error during a step change
The frequency response at zero frequency
Explanation - Steady‑state error is the error remaining after all transients have decayed.
Correct answer is: The difference between input and output as t→∞
Q.70 Which rule can be applied to simplify a feedback loop when the forward path is G(s) and the feedback path is H(s)?
Series rule
Parallel rule
Negative feedback rule
Feedforward rule
Explanation - Negative feedback rule provides the closed‑loop transfer function G/(1+GH).
Correct answer is: Negative feedback rule
Q.71 In a unity negative feedback system, what is the steady‑state error to a unit step input for a type‑1 system?
0
1/K
1
∞
Explanation - A type‑1 system (one integrator) eliminates steady‑state error to a step input.
Correct answer is: 0
Q.72 Which of the following is true for a system with transfer function G(s)= k/(s^2 + 2ζω_ns + ω_n^2) when ζ=0?
The system is critically damped
The system is underdamped and oscillatory
The system is overdamped
The system is unstable
Explanation - ζ=0 yields a pure imaginary pole pair → undamped oscillations.
Correct answer is: The system is underdamped and oscillatory
Q.73 What does the term "system type" indicate in the context of steady‑state error analysis?
The number of integrators in the forward path
The number of integrators in the feedback path
The number of poles in the right half‑plane
The number of zeros in the right half‑plane
Explanation - System type is defined by the number of pure integrators in the open‑loop transfer function.
Correct answer is: The number of integrators in the forward path
Q.74 Which of the following is NOT a valid operation for block diagram reduction?
Series simplification
Parallel simplification
Pole‑zero cancellation in the feedback path
Removing a summing junction with no inputs
Explanation - Pole‑zero cancellation is only valid when the cancellation occurs in the forward path or overall transfer function, not just in the feedback path alone.
Correct answer is: Pole‑zero cancellation in the feedback path
Q.75 In a control system, which of the following statements best describes the effect of increasing the feedback gain?
It increases the system bandwidth and decreases steady‑state error.
It decreases the system bandwidth and increases steady‑state error.
It has no effect on system dynamics.
It makes the system unstable immediately.
Explanation - Higher feedback gain improves bandwidth and reduces steady‑state error, but may reduce stability margins if too high.
Correct answer is: It increases the system bandwidth and decreases steady‑state error.