# Multiple choice question for engineering

## Set 1

1. A minimum phase unity feedback system has a bode plot with a constant slope of -20dB/decade for all frequencies. What is the value of the maximum phase margins of the system?

a) 0°

b) 90°

c) -90°

d) 180°

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2. The range of K for the stability of system is 0<K<100. For K =10, The gain Margin of the system

a) 10

b) 5

c) 0.1

d) 0.5

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3. The frequency at which the Nyquist diagram cuts the unit circle is known as:

a) Gain crossover frequency

b) Phase crossover frequency

c) Damping frequency

d) Corner frequency

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4. The forward path transfer function of a unity feedback system is given by G(s) = 1/(1+s)^{^}2.

What is the phase margin of the system?

a) –π rad

b) 0 rad

c) π/2 rad

d) π rad

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5. Consider the following statements:

1. The delay time is the time required to reach 50% of the final value in the first time.

2. The rise time is the time required for the response to rise from 10% to 90% of its final value for underdamped systems.

3. The rise time is the time required for the response to rise from 0 to 100% for the underdamped systems.

Which of these statements are correct?

a) 1,2 and 3 only

b) 1 and 2 only

c) 1 and 3 only

d) 2 and 3 only negative real axis

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6. For minimum phase systems:

a) Pole must lie on left plane

b) Zeroes must lie on left plane

c) Poles and zeroes must lie on left plane

d) Both must lie on right plane

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7. For non-minimum phase systems:

a) Poles and zeroes must lie on the right s-plane

b) Zeroes must lie on right of s-plane

c) Both lie on left of s-plane

d) Poles must be on the left and zeroes can be on the right s –plane.

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8. For all-pass systems:

a) Poles must lie on right of the s-plane

b) Zeroes must lie on the left of s-plane

c) Poles must lie on the left and zeroes on the mirror image of the pole can be on the right

d) None of the mentioned

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9. All pass system and minimum phase system constitute_________________

a) Pole must lie on left plane

b) Minimum phase system

c) Non-minimum phase system

d) Both must lie on right plane

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10. Minimum phase systems have unique relationship between its phase and magnitude curves

a) True

b) False

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## Set 2

1. The output of a feedback control system must be a function of

a) Reference and output

b) Reference and input

c) Input and feedback signal

d) Output and feedback signal

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2. A control system with excessive noise, is likely to suffer from?

a) Saturation in amplifying stages

b) Loss of gain

c) Vibrations

d) Oscillations

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3. Zero initial condition for a system means?

a) Input reference signal is zero

b) Zero stored energy

c) Initial movement of moving parts

d) System is at rest and no energy is stored in any of its components

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4. Transfer function of a system is used to calculate which of the following?

a) The order of the system

b) The time constant

c) The output for any given input

d) The steady state gain

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5. The band width, in a feedback amplifier.

a) Remains unaffected

b) Decreases by the same amount as the gain increase

c) Increases by the same amount as the gain decrease

d) Decreases by the same amount as the gain decrease

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6. On which of the following factors does the sensitivity of a closed loop system to gain changes and load disturbances depend?

a) Frequency

b) Loop gain

c) Forward gain

d) All of the mentioned

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7. The transient response, with feedback system,

a) Rises slowly

b) Rises quickly

c) Decays slowly

d) Decays quickly

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8. The second derivative input signals modify which of the following?

a) The time constant of the system

b) Damping of the system

c) The gain of the system

d) The time constant and suppress the oscillations

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9. Which of the following statements is correct for any closed loop system?

a) All the co-efficient can have zero value

b) All the co-efficient are always non-zero

c) Only one of the static error co-efficient has a finite non-zero value

d) Only two of the static error co-efficient has a finite non-zero value

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10. Which of the following statements is correct for a system with gain margin close to unity or a phase margin close to zero?

a) The system is relatively stable

b) The system is highly stable

c) The system is highly oscillatory

d) The system is stable

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## Set 3

1. The phase margin (in degrees) of a system having the loop transfer function G(s) H(s)=2√3/s(s+1) is:

a) 45°

b) -30°

c) 60°

d) 30°

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2. The system with the open loop transfer function G(s) H(s) =1/s(s^{^}2+s+1) has the gain margin of :

a) -6 dB

b) 0 dB

c) 3.5 dB

d) 6 dB

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3. The phase angle of the system, G(s) =s+5/s^{2}+4s+9, varies between :

a) 0° and 90°

b) 0° and -90°

c) 0° and -180°

d) -90° and -180°

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4. The polar plot of the transfer function G(s) = 10(s+1)/s+10 will be in the :

a) First quadrant

b) Second quadrant

c) Third quadrant

d) Fourth quadrant

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5. As the polar plot moves toward the point (-1, 0) then the system becomes :

a) Stable

b) Marginally stable

c) Conditionally stable

d) Unstable

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6. Polar plots moving toward the imaginary axis makes the system:

a) Stable

b) Marginally stable

c) Conditionally stable

d) Unstable

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7. The concepts used to measure relative stability are:

a) Phase margin

b) Gain margin

c) Phase and Gain margin

d) Stable

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8. Phase and gain margin are applicable to open and closed loop systems both.

a) True

b) False

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9. Gain margin is:

a) It is a factor by which the system gain can be increased to drive it to the verge of instability

b) It is calculated at gain cross over frequency

c) It is calculated at phase cross over frequency

d) Both a and c

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10. Phase margin is:

a) It is amount of additional phase lag at the gain cross over frequency required to bring the system to the verge of instability

b) It is always positive for stable feedback systems

c) It is calculated at gain cross over frequency

d) All of the mentioned

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## Set 4

1. Consider the block diagram shown below:

If the transfer function of the system is given by T(s)=G1G2+G2G3/1+X. Then X is:

a) G2G3G4

b) G2G4

c) G1G2G4

d) G3G4

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2. For the block diagram given in the following figure, the expression of C/R is:

a) G1G2G3/1-G2G1

b) G1G2/1-G1G2G3

c) G1G2G3/1-G1G2G3

d) G1G2/G3(1-G1G2)

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3. The transfer function from D(s) to Y(s) is :

a) 2/3s+7

b) 2/3s+1

c) 6/3s+7

d) 2/3s+6

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4. The closed loop gain of the system shown in the given figure is :

a) -9/5

b) -6/5

c) 6/5

d) 9/5

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5. The advantage of block diagram representation is that it is possible to evaluate the contribution of each component to the overall performance of the system.

a) True

b) False

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6. The overall transfer function from block diagram reduction for cascaded blocks is :

a) Sum of individual gain

b) Product of individual gain

c) Difference of individual gain

d) Division of individual gain

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7. The overall transfer function of two blocks in parallel are :

a) Sum of individual gain

b) Product of individual gain

c) Difference of individual gain

d) Division of individual gain

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8. Transfer function of the system is defined as the ratio of Laplace output to Laplace input considering initial conditions________

a) 1

b) 2

c) 0

d) infinite

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9. In the following block diagram, G1=10/s G2=10/s+1 H1=s+3, H2=1. The overall transfer function is given by :

a) 10/11s^{2}+31s+10

b) 100/11s^{2}+31s+100

c) 100/11s^{2}+31s+10

d) 100/11s^{2}+31s

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^{2}+31s+100.

10. Oscillations in output response is due to :

a) Positive feedback

b) Negative feedback

c) No feedback

d) None of the mentioned

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## Set 5

1. Assertion (A): Relative stability of the system reduces due to the presence of transportation lag.

Reason (R): Transportation lag can be conveniently handled by Bode plot.

a) Both A and R are true but R is correct explanation of A

b) Both A and R are true but R is correct explanation of A

c) A is true but R is false

d) A is false but R is true

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2. Assertion (A): The phase angle plot in Bode diagram is not affected by the variation in the gain of the system.

Reason(R): The variation in the gain of the system has no effect on the phase margin of the system.

a) Both A and R are true but R is correct explanation of A

b) Both A and R are true but R is correct explanation of A

c) A is true but R is false

d) A is false but R is true

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3. A system has poles at 0.01 Hz, 1 Hz and 80Hz, zeroes at 5Hz, 100Hz and 200Hz. The approximate phase of the system response at 20 Hz is :

a) -90°

b) 0°

c) 90°

d) -180°

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4. The constant M-circle represented by the equation x^{^}2+2.25x+y^{^}2=-1.25 has the value of M equal to:

a) 1

b) 2

c) 3

d) 4

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5. What is the value of M for the constant M circle represented by the equation 8x^{2}+18x+8y^{2}+9=0?

a) 0.5

b) 2

c) 3

d) 8

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6. The constant N loci represented by the equation x^{^}2+x+y^{^}2=0 is for the value of phase angle equal to:

a) -45°

b) 0°

c) 45°

d) 90°

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7. All the constant N-circles in G planes cross the real axis at the fixed points. Which are these points?

a) -1 and origin

b) Origin and +1

c) -0.5 and 0.5

d) -1 and +1

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8. Consider the following statements:

Nichol’s chart gives information about.

i. Closed loop frequency response.

ii. The value of the peak magnitude of the closed loop frequency response Mp.

iii. The frequency at which Mp occurs.

Which of the above statements are correct?

a) 2 and 3

b) 1 and 2

c) 1 and 3

d) 1,2 and 3

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9. Which one of the following statements is correct? Nichol’s chart is useful for the detailed study analysis of:

a) Closed loop frequency response

b) Open loop frequency response

c) Close loop and open loop frequency responses

d) None of the above

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10. In a bode magnitude plot, which one of the following slopes would be exhibited at high frequencies by a 4th order all-pole system?

a) -80dB/decade

b) -40 dB/decade

c) 40 dB/decade

d) 80 dB/decade

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^{4}terms in denominator. One pole exhibits -20dB/decade slope, so 4 pole exhibits a slope of -80 dB /decade.

11. Frequency range of bode magnitude and phases are decided by :

a) The lowest and higher important frequencies of dominant factors of the OLTF

b) The lowest and highest important frequencies of all the factors of the open loop transfer function

c) Resonant frequencies of the second factors

d) None of the above

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12. OLTF contains one zero in right half of s-plane then

a) Open loop system is unstable

b) Close loop system is unstable

c) Close loop system is unstable for higher gain

d) Close loop system is stable

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13. The critical value of gain for a system is 40 and gain margin is 6dB. The system is operating at a gain of:

a) 20

b) 40

c) 80

d) 120

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14. Nichol’s chart is useful for the detailed study and analysis of:

a) Closed loop frequency response

b) Open loop frequency response

c) Close loop and open loop frequency responses

d) open loop and Close loop frequency responses

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15. The roots of the characteristic equation of the second order system in which real and imaginary part represents the :

a) Damped frequency and damping

b) Damping and damped frequency

c) Natural frequency and damping ratio

d) Damping ratio and natural frequency