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# Multiple choice question for engineering

## Set 1

1. A system is said to be_____________ if it is possible to transfer the system state from any initial state to any desired state in finite interval of time.
a) Controllable
b) Observable
c) Cannot be determined
d) Controllable and observable

Answer: a [Reason:] By definition a system is said to be controllable, if it is possible to transfer the system state from any initial state to any desired state in finite interval of time.

2. A system is said to be_________________ if every state can be completely identified by measurements of the outputs at the finite time interval.
a) Controllable
b) Observable
c) Cannot be determined
d) Controllable and observable

Answer: b [Reason:] By definition, a system is said to be observable, if every state can be completely identified by measurements of the outputs at the finite time interval.

3. Kalman’s test is for :
a) Observability
b) Controllability
c) Optimality
d) Observability and controllability

Answer: d [Reason:] Kalman’s test is the test that is done for the controllability and observability by solving the matrix by kalman’s matrix individually for both tests.

4. Consider a system if represented by state space equation and x1 (t) =x2 (t), then the system is:
a) Controllable
b) Uncontrollable
c) Observable
d) Unstable

Answer: b [Reason:] After calculating the matrix which for controllable system and finding the determinant and should not be zero but in this case comes to be zero.

5. For the system , which of the following statements is true?
a) The system is controllable but unstable
b) The system is uncontrollable and unstable
c) The system is controllable and stable
d) The system is uncontrollable and stable

Answer: By Kalman’s stability test the system is uncontrollable and root of the characteristic equation lies on the right side of the s-plane.

6. A transfer function of the system does not have pole-zero cancellation? Which of the following statements is true?
a) System is neither controllable nor observable
b) System is completely controllable and observable
c) System is observable but uncontrollable
d) System is controllable and unobservable

Answer: b [Reason:] If the transfer function of the system does not have pole-zero cancellation then it is completely controllable and observable.

7. Complex conjugate pair:
a) Center
b) Focus point
d) Stable node

Answer: b [Reason:] Complex conjugate pair is the complex pair of the roots of the equation and has a focus point.

8. Pure imaginary pair:
a) Centre
b) Focus point
d) Stable node

Answer: a [Reason:] Pure imaginary pair is the nature of the root of the equation that has no real part only has the nature of center for linearized autonomous second order system.

9. Real and equal but with opposite sign.
a) Center
b) Focus point
d) Stable node

Answer: c [Reason:] Saddle point are real and equal with opposite sign and these points are called the saddle point as the points are different with real and equal with opposite sign.

10. Real distinct and negative.
a) Center
b) Focus point
d) Stable node

Answer: d [Reason:] Stable node is real distinct and negative and this node is stable as the points or roots are real and neative lying on the left side of the plane.

## Set 2

1. Low power transducers called sensors prefer:
a) Linear relationship between controlled variable and output variable
b) Non-functional relationship between controlled variable and output variable
c) Non-linear relationship between controlled variable and output variable
d) Not related with each other

Answer: a [Reason:] Sensors are different from transducers as in transducers the energy is converted from one form to another while in sensors only the energy is sensed not converted and it is possible to get the accurate results in less time.

2. The chief advantage offered by the electronics is:
a) Differencing and stable amplification by Op-Amp
b) Stable amplification of power level by use of power transistor and SCR’s
c) Differencing and stable amplification of power level by Op-Amp
d) No amplification with the Op-Amp

Answer: c [Reason:] Advantage of electronics is that every type of energy is converted into measurable and storage energy and electronically differencing to get the error signal and its amplifier.

3. Which of the motions in actuators are preferred:
a) Translator
b) Rotary
c) Stationary
d) Non-Stationary

Answer: b [Reason:] An actuator in a control systems perform variety of task in hydraulic, pneumatic and electrical system but majorly they are all controlling rotary motions.

4. Assertion (A): Electric actuators are used control system for high torque applications.
Reason (R): Due to linear speed-Torque characteristics.
a) Both A and R are true and R is correct explanation of A
b) Both A and R are true but R is not correct explanation of A
c) A is true but R is false
d) A is false but R is true

Answer: a [Reason:] Electric actuators are the devices that are used to convert non measurable form of energy into measurable and are used in high torque applications due to linear speed torque characteristics but not used in low speed where hydraulic actuators are still used.

5. Low power DC and AC motors are also known as _________
a) Servomotors
b) Tachogenerators
c) A.C. generators
d) D.C. generators

Answer: a [Reason:] Electric actuators are of two kinds’ ac and dc motors and with low power rating they are called ac servomotors.

6. The torque developed by the motor when stationary with the full applied voltage__________
a) Stalled torque
b) Torque
c) Force
d) Couple

Answer: a [Reason:] Stalled torque is the important figure of merit of Servomotor which is important for linearity characteristics.

7. High torque/inertia ratio means:
a) Stalled torque
b) Stalled inertia
c) Stalled toque/inertia ratio
d) Lower motor time constant

Answer: d [Reason:] High torque/inertia ratio means the ration of torque to the inertia should be high as for higher torque the inertia must be very low and this indicates lower time constant as it leads to dynamic response.

8. Electric actuators for stepped motion are known as stepper motor.
a) True
b) False

Answer: a [Reason:] Stepper motors are the motors in which the motion generated is in the form of steps with respect to the time and works on the same principle as electric actuators but with stepped motion.

9. DC motors can be modeled as:
a) Armature controlled
b) Field Controlled
c) Both a and b
d) None of the mentioned

Answer: c [Reason:] DC motors are the motors that work o the direct current and commutators are replaced by slip rings and can be classified based on the construction as armature controlled or field controlled.

10. Assertion (A): Pneumatic actuators are not as messy as hydraulic ones.
Reason (R): Pneumatic suffer from leakages and inherent inaccuracies.
a) Both A and R are true and R is correct explanation of A
b) Both A and R are true but R is not correct explanation of A
c) A is true but R is false
d) A is false but R is true

Answer: b [Reason:] Pneumatic actuators are the devices that convert the motion of air into measurable form of the energy and can also be used in low speed applications but they suffer leakages and inherent in accuracies.

11. DC motors are constructed using:
a) Permanent Magnet
b) Electromagnet.
c) Magnets are not used
d) Plastics

Answer: a [Reason:] DC motors are are the motors that work o the direct current and commutators are replaced by slip rings and now constructed using permanent magnets having high flux density.

12. Permanent magnets used for DC motors because of:
a) High residual flux density
b) High coercivity
c) Both a and b
d) Retentivity

Answer: c [Reason:] Permanent magnets are hard magnets with the area og B-H curve more and they are less used at core of the magnet and are used for DC servomotors as they have high residual flux density and high coercivity.

## Set 3

1. The forward path transfer function of a unity feedback system is given by G(s) = 100/(s2+10s+100). The frequency response of this system will exhibit the resonance peak at:

Answer: c [Reason:] G(s) = 100/(s2+10s+100) wn = 10rad/sec G = 10/2wn =0.5 wr = 0.707 rad/s.

2. Assertion (A): All the systems which exhibit overshoot in transient response will also exhibit resonance peak in frequency response.
Reason (R): Large resonance peak in frequency response corresponds to a large overshoot in transient response.
a) Both A and R are true and R is the correct explanation of A
b) Both A and R are true and R is not the correct explanation of A
c) A is true but R is false
d) A is false but R is true

Answer: a [Reason:] For G<1/√2 frequency parameters ex Mr resonant peak and time response parameters eg. Mp peak overshoot are well correlated. For G>1/√2 the resonant peak Mr does not exist and the correlation breaks down. This is not a serious problem as for this range of G, the step response oscillations are well-damped and Mp is hardly perceptible.

3. The transfer function of a system is given by Y(s)/X(s) = e−0.1s/1+s. If x(t) is 0.5sint, then the phase angle between the output and the input will be:
a) -39.27°
b) -45°
c) -50.73°
d) -90°

Answer: c [Reason:] Phase angle = -tan−1-0.1*180°/π w =1 rad/sec Phase angle =-50.73°.

4. The critical value of gain for the system is 40. The system is operating at a gain of 20. The gain margin of the system is :
a) 2 dB
b) 3 dB
c) 6 dB
d) 4 dB

Answer: c [Reason:] G.M. =Kmarginal/Kdesire Kmarginal =40 Kdesire = 20 G.M. =2 G.M. (dB) = 6dB.

5. The phase angle of the system G(s) =s+5/s2+4s+9;varies between
a) 0° and 90°
b) 0° and -90°
c) 0° and -180°
d) -90° and -180°

Answer: b [Reason:] Phase = tan−1−11w−w3/45−2.

6. The open loop transfer function of a system is :
G(s) H(s) =K/ (1+s) (1+2s) (1+3s)
The phase crossover frequency wpc is:
a) √2
b) 1
c) Zero
d) √3

7. Which one of the following statements is correct for gain margin and phase margin of two closed-loop systems having loop functions G(s) H(s) and exp(-s) G(s) H(s)?
a) Both gain and phase margins of the two systems will be identical
b) Both gain and phase margins of G(s) H(s) will be more
c) Gain margins of the two systems are the same but phase margins of G(s) H(s) will be more
d) Phase margins of the two systems are the same but gain margin of G(s) H(s) will be less

Answer: c [Reason:] The factor exp (-st) is the cause of the term transportation lag (time delay). The effect of e-st term is simply to rotate each point of the G(s) H(s) plot by an angle wT rad in the clockwise direction. So the phase margin of the system reduces as T increases. But since |e-s| =1, therefore the gain margins of both the systems are the same.

8. In a feedback control system, phase margin(PM) is
1. Directly proportional to G
2. Inversely proportional to G
3. Independent of G
4. Zero when G =0
Which of the above statements are correct?
a) 1 and 2
b) 2 and 3
c) 3 and 4
d) 1 and 4

Answer: d [Reason:] For small values of G, PM is directly proportional to G and at G =0. P.M. =0.

9. The gain margin in dBs of a unity feedback control system whose open loop transfer function, G(s) H(s) =1/s(s+1) is
a) 0
b) 1
c) -1
d) ∞

Answer: d [Reason:] wpc = ∞ Magnitude of the transfer function =0 Gain Margin =∞ dB.

10. The loop transfer function of a system is given by G(s) H(s) =10e-Ls/s. The phase crossover frequency is 5rad/s. The value of the dead time L is
a) π/20
b) π/10
c) -π/20
d) Zero

Answer: b [Reason:] – π/2-180/π*L*5 = -π 5L =π/2 L =π/10.

## Set 4

1. Which one of the following statements is correct?
The effects of the phase lead compensator or gain cross over frequency and the bandwidth are:
a) That both are decreased
b) That gain cross over frequency reduces but BW is increased
c) That gain cross over frequency increases but BW is decreased
d) That both are increased

Answer: d [Reason:] Phase lead compensator acts like a high pass filter. So gain crossover frequency and bandwidth both increases.

2. How does cascading an integral controller in the forward path of a control system affect the relative stability (RS) and the steady-state error of that system?
a) RS and SSE are increased
b) RS is reduced nut SSE is increased
c) RS is increased but SSE is reduced
d) RS and SSE are reduced

Answer: d [Reason:] Integral Controller acts like a low pass filter. It reduces the stability as well as steady state error.

3. With regard to the filtering property, the lead compensator and the lag compensator are respectively :
a) Low pass and high pass filters
b) High pass and low pass filters
c) Both high pass filter
d) Both low pass filters

Answer: b [Reason:] Lead compensator is a high pass filter and Lag compensator is a low pass filter.

4. What is the effect of phase-lag compensation on the performance of the servo system?
a) For a given relative stability, the velocity constant is increased
b) For a given relative stability, the velocity constant is decreased
c) The bandwidth of the system is increased
d) The time response is made faster

Answer: a [Reason:] Phase lag compensation is an integrator. It reduces the steady state error. Velocity constant = 1/ (steady state error). So, the velocity constant is increased.

5. Which one of the following is an advantage of a PD controller in terms of damping and natural frequency?
a) G remains fixed but natural frequency increases
b) G remains fixed but natural frequency decreases
c) Natural frequency fixed but G increases
d) Natural frequency fixed but G decreases

Answer: c [Reason:] Comparing with the characteristic equation natural frequency remains fixed but the value of G that increases hence the transient response is improved.

6. Which one of the following is a disadvantage of proportional controller?
a) It is destabilizes the system
b) It produces offset
c) It makes the response faster
d) It has very simple implementation

Answer: b [Reason:] Main disadvantage of proportional controller is produces the permanent error is called offset error.

7. A process is controlled by PID controller. The sensor has high, measurement noise. How can the effect be reduced?
a) By use of bandwidth limited derivative term
b) By use of proportional and derivative terms in the forward path
c) By use of high proportional band
d) By use of low integral gain

Answer: b [Reason:] The effect of noise can be reduced by the use of proportional and derivative controller in the forward path.

8. Consider the following statements for a PI compensator for control system.
1. It is equivalent to adding a zero at origin
2. It reduces overshoot
3. It improves the steady state error of the system
Which of the statements given above are correct?
a) 1 and 3
b) 1,2 and 3 only
c) 2 and 3
d) 1 only

Answer: c [Reason:] PI compensator adds one open loop pole at origin and open loop zero at negative real axis.

9. The input to a controller is :
a) Sensed signal
b) Error signal
c) Desired variable value
d) Signal of fixed amplitude not dependent on desired value

Answer: b [Reason:] Input to the controller is always the parameter of the system which is to be controlled that is the desirable value.

10. What is the characteristic of a good control system?
a) Sensitive to parameter variation
b) Insensitive to the input command
c) Neither sensitive to parameter variations not sensitive to input commands
d) Insensitive to the parameter variation but sensitive to the input commands

Answer: In a good control system, output is sensitive to input variations but insensitive to parameter variations.

## Set 5

1. What should be the nature of bandwidth for a good control system?
a) Large
b) Small
c) Medium
d) All of the mentioned

Answer: a [Reason:] Bandwidth is defined as the difference in the highest frequency and lowest frequency and bandwidth must be large for the good control system and for higher bandwidth noise is also large.

2. Which system exhibits the initiation of corrective action only after the output gets affected?
a) Feed forward
b) Feedback
c) Both a and b
d) None of the mentioned

Answer: b [Reason:] Feedback is the process in which the output of the system is desired by comparing the output with the input and with the feedback system exhibits the initiation of corrective action only after the output gets affected.

3. A good control system should be sensitive to __________
a) Internal disturbances
b) Environmental parameters
c) Parametric variations
d) Input signals (except noise)

Answer: c [Reason:] A good control system is the system with high speed of response and steady state error must be less and bandwidth should be large and noise must be very low and must be sensitive to parametric variations.

4. What is the value of steady state error in closed loop control systems?
a) Zero
b) Unity
c) Infinity
d) Unpredictable

Answer: a [Reason:] Steady state error is the error which is the difference in the final output to the desired output and the value of steady state error for the good control system must be zero.

5. Into which energy signal does the position sensor convert the measured position of servomotor in servomechanisms?
a) Mechanical
b) Electrical
c) Thermal
d) Light

Answer: a [Reason:] In mechanical system the sensors are used in which the mechanical motion is converted into electrical energy and generally in mechanical system position sensor convert the measured position of servomotor in servomechanism.

6. Which among the following controls the speed of D.C. motor?
a) Galvanometer
b) Gauss meter
c) Potentiometer
d) Tachometer

Answer: d [Reason:] D.C. motor is the motor which operates with the direct current as in the construction of DC motors slip rings not commutators and tachometer control the speed of DC motor.

7. Which among the following represents an illustration of closed loop system?
a) Automatic washing machine
b) Automatic electric iron
d) Electric hair drier

Answer: a [Reason:] Closed loop control system is the system with the positive or negative feedback and this is made so as to avoid the disadvantages of open loop control system and in the above options automatic washing machine represents closed loop system.

8. Which notation represents the feedback path in closed loop system representation?
a) b(t)
b) c(t)
c) e(t)
d) r(t)

Answer: c [Reason:] Feedback can be positive and negative and feedback is so used to reduce the error of the system by comparing the final output with the desired output and reducing the error and this error is denoted with the symbol as e(t).

9. Which among the following is not an advantage of an open loop system?
a) Simplicity in construction & design
b) Easy maintenance
c) Rare problems of stability
d) Requirements of system re-calibration from time to time

Answer: d [Reason:] Open loop system is the system with no feedback and the parameter variations in the open loop system are more as compared to the closed loop system and the system has to be re-calibrated as per the requirement as automatic calibration is not present in this system.

10. Which terminology deals with the excitation or stimulus applied to the system from an external source for the generation of an output?
a) Input signal
b) Output signal
c) Error signal
d) Feedback signal