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Multiple choice question for engineering

Set 1

1. A control system in which the control action is somehow dependent on the output is known as
a) Closed loop system
b) Semi closed loop system
c) Open system
d) Non feedback control system

View Answer

Answer: a [Reason:] Closed system is a control system in which the feedback is present that can be positive or negative and in which the control action is somewhat dependent on the output.

2. In closed loop control system, with positive value of feedback gain the overall gain of the system will
a) Decrease
b) Increase
c) Be unaffected
d) Exponentially increase

View Answer

Answer: b [Reason:] Closed loop control system, can be both positive and negative and with positive value of feedback gain where the overall gain of the system will increase and also the oscillations.

3. Which of the following is an open loop control system?
a) Field controlled D.C. motor
b) Ward Leonard control
c) Metadyne
d) Stroboscope

View Answer

Answer: a [Reason:] Open loop control systems are the systems which have no feedback and cannot be used to obtain the desired response and field controlled system is an open loop control system.

4. Which of the following statements is not necessarily correct for open control system?
a) Input command is the sole factor responsible for providing the control action
b) Presence of non-linearities causes malfunctioning
c) Less expensive
d) Generally free from problems of non-linearities

View Answer

Answer: b [Reason:] Open loop control system are the systems which have no feedback and cannot be used to obtain the desired response and non-linearities does not cause malfunctioning.

5. In open loop system
a) The control action depends on the size of the system
b) The control action depends on system variables
c) The control action depends on the input signal
d) The control action is independent of the output

View Answer

Answer: d [Reason:] In open loop system the output cannot be used to obtain the desired response and the control action is independent of the output.

6. ___________has tendency to oscillate.
a) Open loop system
b) Closed loop system
c) Open and closed loop systems have tendency to oscillate
d) No Systems have tendency to oscillate

View Answer

Answer: a [Reason:] Open loop control systems are the systems where the output cannot be the desired output and no feedback is used and gain of the system is very high due to this damping is very less and hence system has tendency to oscillate.

7. A good control system has all the following features except
a) Good stability
b) Slow response
c) Good accuracy
d) Sufficient power handling capacity

View Answer

Answer: b [Reason:] A good control system is mainly negative feedback closed loop control system where the gain of system is not very high and damping is present and no oscillations are present and has fast output response.

8. A car is running at a constant speed of 50 km/h, which of the following is the feedback element for the driver?
a) Clutch
b) Eyes
c) Needle of the speedometer
d) Steering wheel

View Answer

Answer: c [Reason:] For car as control system steering wheel is the feedback element for the driver as for driver to maintain constant speed or desired speed steering wheel is the important element and error detector.

9. The initial response when the output is not equal to input is called
a) Transient response
b) Error response
c) Dynamic response
d) All of the mentioned

View Answer

Answer: a [Reason:] Transient response in the response at any time instant other than final response and this response is at any instant which is mainly dependent on the maximum peak overshoot and settling time.

10. A control system working under unknown random actions is called
a) Computer control system
b) Digital data system
c) Stochastic control system
d) Adaptive control system

View Answer

Answer: c [Reason:] A control system is the system which is having feedback and can be both positive and negative and working under unknown random actions is called stochastic control system.

Set 2

1. The impulse response of a LTI system is a unit step function, then the corresponding transfer function is
a) 1/s
b) 1/s2
c) 1
d) s

View Answer

Answer: a [Reason:] The impulse response of a LTI system is the transfer function itself and hence for the unit step function . As input then the transfer function will be 1/s.

2. For a type one system, the steady – state error due to step input is equal to
a) Infinite
b) Zero
c) 0.25
d) 0.5

View Answer

Answer: b [Reason:] The steady state error is defined as the error between the final value and the desired response and the difference in the value of both will be the steady state error due to step input for type one system is zero.

3. The equation 2s4+s3+3s2+5s+10=0 has roots in the left half of s–plane:
a) One
b) Two
c) Three
d) Four

View Answer

Answer: b [Reason:] The roots of the equation can be calculated using Routh-Hurwitz criterion and hence there are 2 sign changes in the first column of the row and therefore the two roots lie on the right half of s-plane.

4. If the Nyquist plot of the loop transfer function G (s)H (s) of a closed-loop system encloses the (1, j0) point in the G (s)H (s) plane, the gain margin of the system is
a) Zero
b) Greater than zero
c) Less than zero
d) Infinity

View Answer

Answer: c [Reason:] Nyquist plot deals with the open loop poles and zero and equals the encirclements to the open loop poles of the system.

5. Consider the function F (s) =5/s (s2+s+2) , where F (s) is the Laplace transform f (t). Then the final value theorem is equal to
a) 5
b) 5/2
c) Zero
d) Infinity

View Answer

Answer: b [Reason:] Final value theorem is given for the stable system only and this is a type 1 system and for step input the final value can be calculated as 5/2.

6. The transfer function of a phase-lead controller is given by
a) (1+aTs)/(1+Ts) , a>1 T>0
b) (1+aTs)/(1+Ts) , a<1 T>0
c) (1-aTs)/(1+Ts) , a>1 T>0
d) (1±Ts)/(1+Ts) , a<1 T>0

View Answer

Answer: a [Reason:] For the phase lead controller in which the stability and speed of response is more for the system, the magnitude of the pole must be greater than the magnitude of the zero.

7. If the system matrix of a linear time invariant continuous system is given by
Its characteristic equation is given by:
a) s2+5s+3=0
b) s2-3s-5=0
c) s2+3s+5=0
d) s2+s+2=0

View Answer

Answer: a [Reason:] The transfer function is calculated by the state variable analysis and hence the transfer function is calculated by state transition matrix and taking the inverse Laplace transform.

8. Given a unity feedback control system with G (s) = K/s(s+4), the value of K for which the damping ratio is 0.5.
a) 1
b) 16
c) 64
d) 32

View Answer

Answer: b [Reason:] The value is found by using the Routh- Hurwitz criteria and equating one of the row of the Routh-Hurwitz criteria equal to zero and hence finding the value of K.

9. The LVDT is used in the measurement of:
a) Displacement
b) Acceleration
c) Velocity
d) Humidity

View Answer

Answer:a [Reason:] The LVDT is the linear variable differential transformer and it is used to calculate the displacement with the inductor process.

10. A system with gain margin close to unity and phase margin close to zero is :
a) Highly stable
b) Oscillatory
c) Relatively stable
d) Unstable

View Answer

Answer: c [Reason:] A system is relative stable not stable if the phase margin is close to zero then the stability is checked by gain margin.

Set 3

1. The output of the system is considered near :
a) 1
b) 2
c) 3
d) 0

View Answer

Answer: d [Reason:] Our main objective in the optimal control problem is to reduce the performance index of the system as minimize the output and make it near equal to zero.

2. A performance index written in terms of :
a) 1 variable
b) 2 variable
c) 3 variable
d) 5 variable

View Answer

Answer: Generally the performance index be of any variables but in standard form we consider the performance index to be in 2 variable only.

3. Matrix Q is :
a) Positive semi definite symmetric matrix
b) Positive definite non-symmetric matrix
c) Negative definite symmetric matrix
d) Negative definite non-symmetric matrix

View Answer

Answer: a [Reason:] Matrix Q defines positive definite or non-definite symmetric matrix which is used in the performance index so as to give equal weightage to each element.

4. Matrix R is :
a) Positive semi definite symmetric matrix
b) Positive definite non-symmetric matrix
c) Negative definite symmetric matrix
d) Negative definite non-symmetric matrix

View Answer

Answer: a [Reason:] Matrix R defines positive definite or non-definite symmetric matrix which is used in the performance index so as to give equal weightage to each element.

5. The major requirement of making the output of the system small in output regulator problem is :
a) The system must be controllable
b) The system must be stable
c) The system must be observable
d) The system must be LTI

View Answer

Answer: c [Reason:] We are concerned with making the output of the output regulator problem small this is achieved when the system is observable.

6. Minimum principle was given by:
a) Pontryagin
b) Hamiltonian
c) Bellman
d) Jacobi

View Answer

Answer: a [Reason:] The minimum principle to minimize the performance index is given by Pontryagin.

7. Dynamic programming is developed by:
a) Pontryagin
b) Hamiltonian
c) Bellman
d) Jacobi

View Answer

Answer: c [Reason:] Dynamic programming for minimizing the performance index is given by Bellman.

8. The performance index is reduced by:
a) State variable constraint
b) Input constraint
c) Control function minimization
d) Control function constraint

View Answer

Answer: c [Reason:] Once the performance index is calculated the next task is to find the control function which is used to minimize the performance index.

9. Minimum principle is based on :
a) Concepts of calculus of variations
b) Principle of calculus
c) Principle of invariant imbedding
d) Principle of optimality

View Answer

Answer: a [Reason:] Minimum principle of Pontryagin is based on the concept of calculus of variations.

10. Dynamic programming is based on :
a) Principle of calculus
b) Principle of invariant imbedding
c) Principle of optimality
d) All of the mentioned

View Answer

Answer: d [Reason:] Dynamic programming is based on principle of calculus, invariant imbedding and optimality and these are the basic laws of the nature and does not need complex mathematical development to explain its validity.

Set 4

1. The main step for solving the optimal control problem:
a) Transfer function of system which is optimal with respect to the given performance criterion
b) Compensators for the system
c) Minimizing the quadratic function
d) All of the mentioned

View Answer

Answer: d [Reason:] For solving the problem using optimal control problem various steps are required as first is to form the transfer function and then to compute the compensators and the major requirement is to minimize the quadratic function.

2. For minimizing the transfer function the condition is :
a) Second differentiation of the function must be zero
b) Second differentiation of the function must be positive
c) Second differentiation of the function must be negative
d) Second differentiation of the function must be complex

View Answer

Answer: c [Reason:] In optimal control problems the main objective is to reduce the performance criterion which is used only when the second differentiation of the function must be negative.

3. For the stability in optimal control poles of the transfer function must be :
a) Located on the right half of s plane
b) Left half of s plane
c) On the s plane
d) None of the mentioned

View Answer

Answer: b [Reason:] For the stability point of view the basic definition continues that the poles must be located on the left half of s plane.

4. The method of choosing compensator is the configuration must be:
a) Forward path
b) Cascade and feedback compensation
c) Feed forward configuration
d) All of the mentioned

View Answer

Answer: d [Reason:] The above mentioned are the various configurations of choosing a compensator.

5. When some of the states are inaccessible, then we may set the feedback coefficients equal to zero.
a) True
b) False

View Answer

Answer: a [Reason:] This is done to adjust coefficients to realize the transfer function and if it is not possible then reconstruction of signals can be done.

6. Z-transform is used in:
a) Continuous optimal control problem
b) Discrete optimal problem
c) Control systems
d) None of the mentioned

View Answer

Answer: b [Reason:] Z-transform by definition can is used in discrete case only both in optimal and normal control functions.

7. For the stable system in discrete optimal control systems:
a) Poles must lie outside the unit circle
b) Poles must lie within the unit circle
c) Poles must be on the unit circle
d) Pole must be in infinity

View Answer

Answer: b [Reason:] Poles in discrete system must be inside the unit circle and for causal system it must be outside the circle but no including the infinity.

8. The special case of the tracking problem with input equal to zero:
a) Free response
b) Regulator problem
c) Forced response
d) Output regulator problem

View Answer

Answer: d [Reason:] For zero input output is zero if all the initial conditions are zero the response are due to non-initial conditions which are caused due to disturbances.

9. The primary objective of the output regulator problem is to damp out:
a) Initial conditions quickly
b) Reducing the effect of excessive oscillations
c) Reducing the effect of excessive overshoot
d) All of the mentioned

View Answer

Answer: d [Reason:] The primary objective of the output regulator problem is to damp out the initial conditions quickly and also reduce the effect of excessive oscillations and overshoot.

10. The limitation of the transfer function approach are:
a) The spectral factorization becomes quite complex
b) It is restricted to the systems with all performance index
c) Multi input and multi output systems are not obvious
d) It is useful for time varying and linear systems

View Answer

Answer: a [Reason:] The limitation of transfer function approach is that is it useful only for quadratic performance index and multi input and multi output systems are obvious and also it is ineffective for time varying and non-linear systems.

Set 5

1. For output regulator problem in performance index the parameter which is set to zero:
a) Input vector
b) Output vector
c) Control vector
d) State vector

View Answer

Answer: b [Reason:] As the problem is to minimize the performance index involving output vector then the output vector must be close to zero.

2. In tracking problem the parameter reduced is :
a) Error
b) Output
c) Input
d) State

View Answer

Answer: a [Reason:] In tracking problem the main objective is to reduce error and this is the main concern so as to reduce error.

3. Riccati equation is formed by using:
a) Output regulator problem
b) Finite state regulator problem
c) Infinite state regulator problem
d) Tracking problem

View Answer

Answer: d [Reason:] Riccati equation can be formed using the results of the tracking problem as it is mainly applied in the cases where the errors are reduced to the minimum.

4. The value of K must further follow the following constraint that the closed loop system must be:
a) Asymptotically stable
b) Stable
c) Marginally stable
d) Conditionally stable

View Answer

Answer: a [Reason:] The value of Ki must further follow the following constraint that the closed loop system must be asymptotically stable and this is due to the fact that the value of k matrix can be varied.

5. For suboptimal control the value of R is assumed to be:
a) Positive definite
b) Non-positive definite
c) Negative
d) Complex

View Answer

Answer: b [Reason:] For suboptimal control the value of R is not assumed to be positive definite but it can also be assumed to be zero.

6. Which one of the following compensation is required for improving the transient response of the system?
a) Phase lead compensation
b) Phase lag compensation
c) Gain compensation
d) Both phase lag compensation and gain compensation

View Answer

Answer: a [Reason:] For increasing or improving the transient response derivative controller is used and which is the phase lead compensation.

7. Pneumatic controller
a) Flexible operation
b) High torque high speed operation
c) Fire and explosion proof operation
d) No leakage

View Answer

Answer: c [Reason:] Pneumatic controllers are fire and explosion proof operation as they require air and gas fuel for its operation.

8. Hydraulic controller:
a) Flexible operation
b) High torque high speed operation
c) Fire and explosion proof operation
d) No leakage

View Answer

Answer: b [Reason:] Hydraulic controller must have no leakage and also it requires high torque and high speed operation due to high density of the controller.

9. Electronic Controller:
a) Flexible operation
b) High torque high speed operation
c) Fire and explosion proof operation
d) No leakage

View Answer

Answer: a [Reason:] Flexible in all sense as it does not require heavy components or extra torque or high speed operations.

10. Which one of the following statement is correct?
A plant controlled by a proportional controller. If a time delay element is introduced in the loop its:
a) Phase margin remains the same
b) Phase margin increases
c) Phase margin decreases
d) Gain margin increases

View Answer

Answer: c [Reason:] The introduction of a time delay element decreases both the phase and gain margin.