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Multiple choice question for engineering

Set 1

1. The unit impulse response of a second order system is 1/6e-0.8tsin(0.6t). Then the natural frequency and damping ratio of the system are respectively.
a) 1 and 0.6
b) 1 and 0.8
c) 2 and 0.4
d) 2 and 0.3

Answer: b [Reason:] 1/10[1/(s2+1.6s+1)] w = 1 rad/s 2Gw = 1.6 G = 0.8.

2. In a RLC series circuit, if the resistance R and inductance L are kept constant but capacitance C is decreased, then which one of the following statements is/are correct?
1. Time constant of the circuit is changed.
2. Damping ratio decreases.
3. Natural frequency increases.
4. Maximum overshoot is unaffected.
a) 1 and 2
b) 2 only
c) 2 and 3
d) 3 and 4

Answer: c [Reason:] G = R/2[√C/L] C decreases, G decreases i.e., damping ratio decreases w = 1/√LC Time constant = 2L/R As C decreases, time constant remains unaffected.

3. Consider the following system shown in the diagram :

If the system shown in the above diagram x (t) = sint. What will be the response y (t) in the steady state?
a) sin(t-45)/√2
b) sin(t+45)/√2
c) √2e-5sint
d) sint-cost

Answer: b [Reason:] Y(s) = [-1/2]/s+1+ [1/2]/(s^2+1) + [s/2]/(s^2+1) y(t)= 1/2e-t+ ½[cost+sint].

4. For critically damped second order system, if the gain constant(K) is increased, the system behavior
a) Becomes oscillatory
b) Becomes under damped
c) Becomes over damped
d) Shows no change

Answer: b [Reason:] Gain of the closed loop system is inversely proportional to the damping and hence if the gain of the system is increased then the damping is reduced and becomes less than 1 system becomes undamped .

5. As unity feedback system has a forward path transfer function G(s) = K/s(s+8) where K is the gain of the system. The value of K, for making this system critically damped should be
a) 4
b) 8
c) 16
d) 32

Answer: c [Reason:] Overall transfer function M(s) = K/K+s(s+8) Therefore the characteristic equation is s2+8s+K w = √K , 2Gw = 8 w = 4 and K = 16.

6. Assertion (A): It is desirable that the transient response be sufficiently fast and sufficiently damped.
Reason (R): Oscillations are not tolerated in the transient response.
a) Both A and R are true but R is not the correct explanation of A
b) Both A and R are true but R is correct explanation of A
c) A is true and R is false
d) A is false and R is true

Answer: b [Reason:] Oscillations must not be present in the transient response as it makes the response slow and sluggish and with positive feedback oscillations are increased and hence positive feedback is not used frequently.

7. The maximum overshoot and rise time conflict with each other.
a) True
b) False

Answer: a [Reason:] For the system to be stable the rise time must be less so that the speed of response is increased and maximum peak overshoot should also be less.

8. The maximum overshoot is:
a) To measure the relative stability
b) A system with large overshoot is desirable
c) It occurs at second overshoot
d) Both b and c

Answer: a [Reason:] It is given time domain specification and system is desirable with small overshoot and it occurs at first over shoot.

9. The second order approximation using dominant pole concept of a system having transfer function 5/(s+5)(s2+s+1) is:
a) 5/(s2+s+1)
b) 1/(s2+s+1)
c) 1/(s+5)(s+1)
d) 5/(s+5)(s+1)

Answer: b [Reason:] Given, T.F. = 5/(s+5)(s2+s+1) Neglecting the insignificant pole, s=5 T.F = 1/(s2+s+1).

10. For the system, C(s)/R(s) = 16/(s2+8s+16). The nature of the response will be
a) Overdamped
b) Underdamped
c) Critically damped
d) None of the mentioned

Answer: c [Reason:] Compare the equation with the characteristic equation s2+2Gws+w2. Then the value of w = 4 and value of G = 1 hence the system is critically damped with poles on the imaginary axis.

Set 2

1. Scientist Bode have contribution in :
a) Asymptotic plots
b) Polar plots
c) Root locus technique
d) Constant M and n circle

Answer: a [Reason:] Asymptotic plots are the bode plots that are drawn to find the relative stability of the system by finding the phase and gain margin and this was invented by Scientist Bode.

2. Scientist Evans have contribution in :
a) Asymptotic plots
b) Polar plots
c) Root locus technique
d) Constant M and n circle

Answer: c [Reason:] Root locus technique is used to find the transient and steady state response characteristics by finding the locus of the gain of the system and this was made Scientist Evans .

3. Scientist Nyquist have contribution in:
a) Asymptotic plots
b) Polar plots
c) Root locus technique
d) Constant M and n circle

Answer: b [Reason:] Nyquist plot is used to find the stability of the system by open loop poles and zeroes and the encirclements of the poles and zeroes and satisfying the equation N=P-Z and this is named under the name of scientist Nyquist.

4. For a stable closed loop system, the gain at phase crossover frequency should always be:
a) < 20 dB
b) < 6 dB
c) > 6 dB
d) > 0 dB

Answer: d [Reason:] Phase crossover frequency is the frequency at which the gain of the system must be 1 and for a stable system the gain is decibels must be 0 db.

5. Which one of the following methods can determine the closed loop system resonance frequency operation?
a) Root locus method
b) Nyquist method
c) Bode plot
d) M and N circle

Answer: d [Reason:] Closed loop system resonance frequency is the frequency at which maximum peak occurs and this frequency of operation can best be determined with the help of M and N circle.

6. If the gain of the open loop system is doubled, the gain of the system is :
a) Not affected
b) Doubled
c) Halved
d) One fourth of the original value

Answer: a [Reason:] Gain of the open loop system is doubled then the gain of the system is not affected as the gain of the system is not dependent on the overall gain of the system.

7. Which one of the following statements is correct?
Nichol’s chart is useful for the detailed study of:
a) Closed loop frequency response
b) Open loop frequency response
c) Close loop and open loop frequency responses
d) None of the mentioned

Answer: a [Reason:] Nichol’s chart has constant M and N circles that are used to find the stability of the system and the detailed study of their can be determined with the help of the closed loop frequency response.

8. Constant M- loci:
a) Constant gain and constant phase shift loci of the closed-loop system.
b) Plot of loop gain with the variation in frequency
c) Circles of constant gain for the closed loop transfer function
d) Circles of constant phase shift for the closed loop transfer function

Answer: d [Reason:] By definition, Constant M loci are Circles of constant phase shift for the closed loop transfer function.

9. Constant N-loci:
a) Constant gain and constant phase shift loci of the closed-loop system.
b) Plot of loop gain with the variation in frequency
c) Circles of constant gain for the closed loop transfer function
d) Circles of constant phase shift for the closed loop transfer function

Answer: c [Reason:] Constant N loci are the circles of constant gain for the closed loop transfer function and the intersection point of the M and N is always the point (-1,0).

10. Nichol’s chart:
a) Constant gain and constant phase shift loci of the closed-loop system.
b) Plot of loop gain with the variation in frequency
c) Circles of constant gain for the closed loop transfer function
d) Circles of constant phase shift for the closed loop transfer function

Answer: b [Reason:] Nichol’s chart are plot of loop gain with the variation in frequency and this is used to determine the stability of the system with the variation in the frequency.

Set 3

1. Consider a simple mass spring friction system as given in the figure K1, K2 are spring constants f-friction, M-Mass, F-Force, x-Displacement. The transfer function X(s)/F(s) of the given system will be :

a) 1/(Ms2+fs+K1.K2)
b) 1/(Ms2+fs+K1+K2)
c) 1/(Ms2+fs+K1.K2/K1+K2)
d) K2/(Ms2+fs+K1)

Answer: b [Reason:] Force balance equations are formed where force from both the springs will be balanced by the mass system.

2. The output of an first order hold between two consecutive sampling instants is:
a) Constant
c) Ramp Function
d) Exponential Function

Answer: c [Reason:] Inverse Laplace of the equation of first order hold gives the ramp function and hence the output of an first order hold between two consecutive sampling is ramp function.

3. Which of the following is an example of an open loop system?
a) Household Refrigerator
b) Respiratory system of an animal
c) Stabilization of air pressure entering into the mask
d) Execution of program by computer

Answer: d [Reason:] Execution of a program by a computer is an example of an open loop system as the feedback mechanism is not taken by the computer program and set programs are used to get the set output.

4. A tachometer is added to servomechanism because:
c) It reduces steady state error
d) It converts velocity of the shaft to a proportional Dc voltage

Answer: b [Reason:] A tachometer is a device to control the speed and adjust damping and it is used in servomechanism to adjust damping and mainly is used in AC servomotors.

5. A synchro Transmitter is used with control transformer for:
a) Feedback
b) Amplification
c) Error detection
d) Remote sensing

Answer: c [Reason:] Synchro transmitter is used as the error detector to get the desired speed and it is accompained with the synchro transformer which is used as an amplifier.

6. The below figure represents:

b) Lag network
c) PI controller
d) PD controller

Answer: b [Reason:] The equations of performance are B1(dX1/dt-dX2/dt)+k1(X1-X0)=k2X0 T=k1(1+B1s/K1)/k1+k2(1+sB1/k1+k2) X0(s)/X1(s)=1/a(1+aTs/1+Ts).

7. Backlash in a stable control system may cause:
a) Under damping
b) Over damping
c) High level oscillations
d) Low level oscillations

Answer: d [Reason:] In a servo system, the gear backlash may cause sustained oscillations or chattering phenomenon and the system may even turn unstable for large backlash.

8. Tachometer feedback in a D.C. position control system enhances stability?
a) True
b) False

Answer: a [Reason:] Tachometer feedback is derivative feedback and hence increases the stability and speed of response, so tachometer adds zero at origin.

9. For a tachometer, if a(t) is the rotor displacement, e(t) is the output voltage and K is the tachometer constant, then the transfer function is given by:
a) Ks2
b) K/s
c) Ks
d) K

Answer: c [Reason:] e(t)=Kw E(s)=Ksa(s) E(s)/a(s)=Ks.

10. Gear train in the motor is used to reduce the gear ratio?
a) True
b) False

Answer: b [Reason:] Gear ratio refers to the ratio of the number of teeths in the respective gears and gear train in the motor is specifically used to increase the gear ratio.

11. Assertion (A): Servomotors have heavier rotors and lower R/X ratio as compared to ordinary motors of similar ratings.
Reason (R): Servomotor should have smaller electrical and mechanical time constants for faster response.
a) Both A and R are true and R is the 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: d [Reason:] Ac servomotors are essentially induction motor with low X/R ratio for the rotor which has very low inertia.

12. Assertion (A): DC servomotors are more commonly used in armature controlled mode than field controlled mode.
Reason (R): Armature controlled Dc motors have higher starting torque than fiels controlled motors.
a) Both A and R are true and R is the 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:] To get higher speed in field controlled dc motor, field current is decreased with decrease in torque.

13. In case of DC servomotor, the back emf is equivalent to an “electric friction” which tends to:
a) Slowly decrease the stability of the system
b) Improve stability of the system
c) Very rapidly decrease the stability of the system
d) Have no effect of stability

Answer: b [Reason:] As Back emf in dc servomotors provides necessary centrifugal force to control the speed of the motor that increases the stability of the system.

14. The lagrangian is defined as:
a. Sum of kinetic energy and hydraulic energy
b. Mechanical energy
c. Difference of kinetic and potential energy
d. None of these

Answer: c [Reason:] By definition lagrangian is defined as difference of kinetic and potential energy. L=K-P.

15. A gantry robot consists of a manipulator mounted on an overhead system that allows movement only in ________ plane.
a) Horizontal
b) Inclined
c) Vertical
d) None of the mentioned

Answer: a [Reason:] Gantry robot allows motion only in horizontal plane and this is made in this geometry to fulfill the respective work.

16. An object stationary or moving in a uniform motion w.r.t A will appear to be traveling in a straight path w.r.t B. This apparent path is attributed to Coriolis acceleration.
a) True
b) False

Answer: b [Reason:] An object stationary or moving in a uniform motion w.r.t A will appear to be traveling in a curved path w.r.t B. This apparent path curvature is attributed to Coriolis acceleration.

Set 4

1. State variable analysis has several advantages overall transfer function as:
a) It is applicable for linear and non-linear and variant and time-invariant system
b) Analysis of MIMO system
c) It takes initial conditions of the system into account
d) All of the mentioned

Answer: d [Reason:] State variable analysis has several advantages overall transfer function as it is applicable for linear and non-linear and variant and time-invariant system, analysis of MIMO system, it takes initial conditions of the system into account.

2. The minimum number of states require to describe the two degree differential equation:
a) 1
b) 2
c) 3
d) 4

Answer: b [Reason:] The number of states required to describe a network is equal to the number of energy storing elements in the electrical network.

3. For a system with the transfer function H(s) = 3(s-2)/s3+4s2-2s+1 , the matrix A in the state space form is equal to:

Answer: b [Reason:] Taking the inverse Laplace of the equation and converting it into differential equation and solving the state space by considering various matrices.

4. The transfer function Y(s)/U(s) of a system described by the state equations dx/dt=-2x+2u and y(t) = 0.5x is:
a) 0.5/(s-2)
b) 1/(s-2)
c) 0.5/(s+2)
d) 1/(s+2)

Answer: d [Reason:] Taking Laplace transform of the equation X(s) = 2U(s)/(s+2) Then Y(s)/U(s) =1/(s+2).

5. A linear time invariant single input single output system has the state space model given by dx/dt=Fx+Gu, y=Hz, where . Here, x is the state vector, u is the input, and y is the output. The damping ratio of the system is:
a) 0.25
b) 0.5
c) 1
d) 2

Answer: b [Reason:] T(s) = 1/(s2+2s+4) G = 0.5.

6. Given the matrix the Eigen value are___________
a) 1,2,3
b) 1
c) -1,-2,-3
d) 0

Answer: c [Reason:] Solving the characteristic equation|SI-A| =0.

7. A transfer function of control system does not have pole-zero cancellation. Which one 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 but unobservable

Answer: b [Reason:] If the input-output transfer function of a linear time-invariant system has pole-zero cancellation, the system will be neither controllable nor observable.

8. The analysis of multiple input multiple output is conveniently studied by;
a) State space analysis
b) Root locus approach
c) Characteristic equation approach
d) Nicholas chart

Answer: a [Reason:] State space analysis is different from the transfer function approach as this can be used for the analysis of multiple input and multiple output system.

9. The state equation in the phase canonical form can be obtained from the transfer function by:
b) Direct decomposition
c) Inverse decomposition
d) Parallel decomposition

Answer: d [Reason:] The state equation from transfer function by parallel decomposition in the phase canonical form.

10. A logarithmic spiral extending out of the singular point is__________
a) Stable
b) Unstable focus
c) Conditionally stable
d) Marginally stable

Answer: b [Reason:] Unstable focus is a logarithmic spiral extending out of the singular point.

Set 5

1. Which of the following programs is not a popular desktop publishing program?
b) Microsoft Publisher
c) Lotus AmiPro
d) QuarkXPress

Answer: c [Reason:] Lotus AmiPro is a word processing package.

2. Programs used to create or modify bitmap images are called __________
a) Illustration programs
b) Paint programs
c) Graphical modifiers
d) Bit publishing packages

Answer: b [Reason:] Image editors (also known as paint programs) are programs for creating and editing bitmap images.

3. Paint programs and image editors are used for creating and editing __________
a) Bitmap images
b) Vector images
c) Text
d) HTML codes

Answer: a [Reason:] Paint programs and image editors are programs for creating and editing bitmap images.

4. Raster images are also known as :
a) Bitmap images
b) Vector images
c) Clip art images
d) Multimedia images

Answer: a [Reason:] Raster images are also known as bitmap images.

5. Images made up of thousands of pixels are called ___________
a) Bitmap
b) Vector
c) Story boards
d) Graphics

Answer: a [Reason:] Bitmap images use thousands of dots or pixels to represent images.

6. Which of the following programs is not a popular professional image editor program?
b) Microsoft Paint
d) Corel Photo Paint

7. Vector images are __________
a) Composed of pixels
b) Composed of thousands of dots
c) Slightly more difficult to manipulate than other images
d) Composed of objects such as lines, rectangles, and ovals

Answer: d [Reason:] Vector images use geometric shapes or objects.

8. Programs used to create or modify vector images are called __________
a) Illustration programs
b) Image editors
c) Graphical modifiers
d) Bit publishing packages

Answer: a [Reason:] Illustration programs (also known as drawing programs) are used to create and to edit vector images.

9. CorelDraw is an example of a(n) __________
a) Groupware application
b) Bit publishing package
c) Paint program
d) Graphics suite