Multiple choice question for engineering
Set 1
1. Unit step response of the system described by the equation y(n) +y(n-1) =x(n) is:
a) z2/(z+1)(z-1)
b) z/(z+1)(z-1)
c) z+1/z-1
d) z(z-1)/z+1
Answer
Answer: a [Reason:] Response of the system is calculated by taking the z-transform of the equation and input to the transfer function in the step input.
2. Inverse z-transform of the system can be calculated using:
a) Partial fraction method
b) Long division method
c) Basic formula of the z-transform
d) All of the mentioned
Answer
Answer: d [Reason:] Inverse z-transform is the opposite method of converting the transfer function in Z domain to the discrete time domain and this can be calculated using all the above formulas.
3. Assertion (A): The system function
H(z) = z3-2z2+z/z2+1/4z+1/s is not causal
Reason (R): If the numerator of H (z) is of lower order than the denominator, the system may be causal.
a) Both A and R are true and R is correct explanation of A
b) Both A and R are true and R is not correct Explanation of A
c) A is True and R is false
d) A is False and R is true
Answer
Answer: a [Reason:] The transfer function is not causal as for causality the numerator of H (z) is of lower order than the denominator, the system may be causal.
4. Assertion (A): Z-transform is used to analyze discrete time systems and it is also called pulsed transfer function approach.
Reason(R): The sampled signal is assumed to be a train of impulses whose strengths, or areas, are equal to the continuous time signal at the sampling instants.
a) Both A and R are true and R is correct explanation of A
b) Both A and R are true and R is not correct Explanation of A
c) A is True and R is false
d) A is False and R is true
Answer
Answer: a [Reason:] Z-transform is used to convert the discrete time systems into the z domain and it is also called pulsed transfer function approach that is justified only at the sampling instants.
5. The z-transform corresponding to the Laplace transform G(s) =10/s(s+5) is
Answer
Answer: b [Reason:] Laplace transform is the technique of relating continuous time to the frequency domain while the z transform is relating discrete time hence Laplace transform is first converted into time domain and then the z transform is calculated.
6. Homogeneous solution of: y(n) -9/16y(n-2) = x(n-1)
a) C1(3/4)n+C2(3/4)-n
b) C1-(3/4)n-1+C2(3/4)n-1
c) C1(3/4)n
d) C1-(3/4)n
Answer
Answer: a [Reason:] Taking the z-transform of the given difference equation and solving the homogeneous equation and finding the solution using complimentary function.
7. If the z transform of x(n) is X(z) =z(8z-7)/4z2-7z+3, then the final value theorem is :
a) 1
b) 2
c) ∞
d) 0
Answer
Answer: a [Reason:] Final value theorem is calculated for the transfer function by equating the value of z as 1 and this can be calculated only for stable systems.
8. Final value theorem is used for:
a) All type of systems
b) Stable systems
c) Unstable systems
d) Marginally stable systems
Answer
Answer: b [Reason:] Final value theorem is used to calculate the final value as for time infinite and for z = 1 the final value theorem can be calculated and final value theorem is for for stable systems.
9. If the z-transform of the system is given by
H (z) = a+z-1/1+az-1
Where a is real valued:
a) A low pass filter
b) A high pass filter
c) An all pass filter
d) A bandpass filter
Answer
Answer: c [Reason:] The discrete time frequency response will be aperiodic and does not depend on the frequency and the transfer function will be representing the all pass filter.
10. The system is stable if the pole of the z-transform lies inside the unit circle
a) True
b) False
Answer
Answer: a [Reason:] For the system to be stable in Z domain the pole in the this domain must lie inside the unit circle and for the causal stable region must be outside the circle and hence the locus will be a ring.
Set 2
1. A proportional controller leads to:
a) Zero steady state error for step input for type 1 system
b) Zero steady state error for step input for type 0 system
c) Infinite steady state error for step input for a type 1 system
d) Finite steady state error for step input for type 1 system
Answer
Answer: a [Reason:] A proportional controller is the controller block used in the system so as to follow the output and leads to zero steady state error for step input for type 1 system.
2. An all-pass network imparts only
a) Negative phase to the input
b) Positive phase to the input
c) 90 degree phase shift to the input
d) 180 degree phase shift to the input
Answer
Answer: d [Reason:] An all-pass network is the network that is the combination of the minimum and non-minimum phase systems and have the magnitude 1 for all frequencies and imparts only 180 degree phase shift.
3. Which of the following is an effect of lag compensation?
a) Decrease bandwidth
b) Improves transient response
c) Increases the effect of noise
d) Increases stability margin
Answer
Answer: a [Reason:] Lag compensation is the integral compensation that introduces the lag in the response by slowing the response and reducing the steady state error value by decreasing bandwidth.
4. PD controller:
a) Decreases steady state error and improves stability
b) Rise time decreases
c) Transient response becomes poorer
d) Increases steady state error
Answer
Answer: b [Reason:] In Proportional and Derivative controller the damping factor value is increases the oscillations are reduced and rise time decreases hence speed of response increases.
5. PID controller:
a) Decreases steady state error and improves stability
b) Rise time decreases
c) Transient response becomes poorer
d) Increases steady state error
Answer
Answer: a [Reason:] Proportional Integral and Derivative controller is the controller that is the combinational controller that increases the speed of response, decreases steady state error and improves stability.
6. PI controller:
a) Decreases steady state error and improves stability
b) Rise time decreases
c) Transient response becomes poorer
d) Increases steady state error
Answer
Answer: c [Reason:] In Proportional and Integral controller which is the extension of the integral controller which improves the steady state response but transient response becomes poorer.
7. Proportional controller
a) Decreases steady state error and improves stability
b) Rise time decreases
c) Transient response becomes poorer
d) Increases steady state error
Answer
Answer: d [Reason:] Proportional controller is the controller that is used in the system so that the output follows the input and increases steady state error.
8. PD controller is used to compensate a system, Compared to the uncompensated system, the compensated system has:
a) A higher type number
b) Reduced damping
c) Higher noise amplification
d) Large transient overshoot
Answer
Answer: c [Reason:] The compensated system of the proportional derivative controller has bandwidth increases and signal to noise ratio decreases.
9. Lead compensator increases bandwidth
a) True
b) False
Answer
Answer: a [Reason:] Lead compensator is similar to high pass filter and causes lead in the system and increases the speed of response of the system and hence increases Bandwidth.
10. Lag compensator reduces__________
a) Position constant
b) Velocity constant
c) Position variable
d) Acceleration constant
Answer
Answer: b [Reason:] Lag compensator is the integral compensation that causes the lag in the response and reduces velocity constant.
Set 3
1. Closed loop frequency response is very useful as :
a) It approximately predicts the time response of the systems
b) Time response are converted into time domain specifications
c) After design time domain specification is converted into frequency domain
d) All of the mentioned
Answer
Answer: d [Reason:] Closed loop frequency response is very useful as it enables to use second order correlations between frequency and transient response.
2. Maximum peak overshoot in time domain corresponds to :
a) Resonance peak
b) Resonant frequency
c) Bandwidth
d) Cut-off rate
Answer
Answer: a [Reason:] Resonance peak in frequency domain correspond to maximum peak overshoot in time domain.
3. Frequency of oscillation in time domain correspond to :
a) Resonance peak
b) Resonant frequency
c) Bandwidth
d) Cut-off rate
Answer
Answer: b [Reason:] Resonant frequency in frequency domain correspond to frequency of oscillation in time domain.
4. Bandwidth is :
a) Range of frequencies for which the system gain is more than-3dB
b) This is considered good range for transmission of signals
c) For better communication bandwidth of signal must be less
d) All of the mentioned
Answer
Answer: d [Reason:] Bandwidth of a signal must be less but channel must be more foe better transmission or communication.
5. Cut-off rate is the ability of the system to distinguish the signal from _____________
a) Bandwidth
b) Noise
c) Resonance peak
d) Magnitude
Answer
Answer: b [Reason:] Cut-off rate is the ability of the system to distinguish the signal from noise.
6. The important figures of merit to the system in frequency domain are :
a) Maximum value of resonant peak
b) Value of resonance frequency
c) Maximum value of resonant peak and Value of resonance frequency
d) Minimum value of resonance frequency
Answer
Answer: c [Reason:] The important figures of merit to the system in frequency domain are maximum value of resonance peak and frequency at which it occurs.
7. In q(s) plane Nyquist plot is symmetrical about the :
a) Imaginary axis
b) Real axis
c) Origin
d) None of the mentioned
Answer
Answer: b [Reason:] By definition, In q(s) plane Nyquist plot is symmetrical about the real axis.
8. A polar plot intersects the unit circle at a point making -45° to the negative real axis then the phase margin of the system is :
a) -45°
b) 45°
c) 180°-45°
d) 180°+45°
Answer
Answer: b [Reason:] As the angle is with the negative real axis hence the Phase margin will be 45°.
9. The parameter which is constant along the constant N circle :
a) Frequency
b) Phase angle
c) Magnitude
d) Open loop gain
Answer
Answer: b [Reason:] Phase angle remains constant in constant N-circle.
10. In second order system gain margin is :
a) Zero value
b) Finite value
c) Infinite value
d) None of the mentioned
Answer
Answer: c [Reason:] Gain margin is defined generally for systems with order greater than 3.
Set 4
1. The term backlash is associated with:
a) Servomotors
b) Induction relays
c) Gear trains
d) Tacho generator.
Answer
Answer: c [Reason:] The term backlash is associated with Gear trains.
2. With feedback _____ increases.
a) System stability
b) Sensitivity
c) Gain
d) Effects of disturbing signals
Answer
Answer: a [Reason:] Feedback can increase system stability as well as can reduce the stability of the stable system.
3. By which of the following the system response can be tested better?
a) Ramp input signal
b) Sinusoidal input signal
c) Unit impulse input signal
d) Exponentially decaying signal
Answer
Answer: c [Reason:] System response can be best treated with the impulse response as when the input is impulse input then the output is itself the response of the transfer function.
4. In a system zero initial condition means that :
a) The system is at rest and no energy is stored in any of its components
b) The system is working with zero stored energy
c) The system is working with zero reference signal
d) Laplace transform is not possible
Answer
Answer: a [Reason:] In system zero initial condition means the system is at rest and no energy is stored in the system previously.
5. In a system low friction co-efficient facilitates:
a) Reduced velocity lag error
b) Increased velocity lag error
c) Increased speed of response
d) Reduced time constant of the system
Answer
Answer: a [Reason:] In a system low friction facilitates reduced velocity error as the friction error is equal to the velocity error.
6. Hydraulic torque transmission system is analog of :
a) Amplidyne set
b) Resistance-capacitance parallel circuit
c) Motor-generator set
d) Any of the mentioned
Answer
Answer: c [Reason:] Hydraulic torque transmission system is analog of Motor-generator set.
7. Spring constant in force-voltage analogy is analogous to?
a) Capacitance
b) Reciprocal of capacitance
c) Current
d) Resistance
Answer
Answer: b [Reason:] Spring constant in force-voltage analogy is analogous to reciprocal of the resistance which is also series analogy.
8. The frequency and time domain are related through which of the following?
a) Laplace Transform and Fourier Integral
b) Laplace Transform
c) Fourier Integral
d) Either b or c
Answer
Answer: a [Reason:] The frequency and time domain mainly continuous time domain are related by the Laplace and Fourier transform and discrete time and frequency are related by the discrete time Fourier transform and z transform.
9. An increase in gain, in most systems, leads to:
a) Smaller damping ratio
b) Larger damping ratio
c) Constant damping ratio
d) Zero damping ratio
Answer
Answer: a [Reason:] Damping factor is inversely proportional to the gain and if the gain increases the damping factor and hence the value reduces.
10. Static error co-efficient are used as a measure of the effectiveness of closed loop systems for specified ________ input signal.
a) Acceleration
b) Velocity
c) Position
d) All of the mentioned
Answer
Answer: d [Reason:] Static error coefficients are used as a measure of the effectiveness of closed loop system for specified acceleration, velocity and position of input signal.
Set 5
1. Assertion (A): The closed loop stability can be determined from the poles of an open loop system and the polar plot of the frequency response.
Reason (R): Unstable system has right half poles.
a) Both A and R are true and R is correct explanation of A
b) Both A and R are true and R is not correct Explanation of A
c) A is True and R is false
d) A is False and R is true
Answer
Answer: b [Reason:] Closed loop system can be made stable if the poles of the closed loop system are all lying on the left half of the plane and this can be determined from the poles of an open loop system.
2. The open loop control transfer function of a unity feedback system is given by :
G(s) =K/(s+2)(s+4)(s^2+6s+25)
Which is the value of K which causes sustained oscillations in the closed loop system?
a) 590
b) 790
c) 990
d) 1190
Answer
Answer: a [Reason:] The value of the sustained oscillations is calculated from the Rout-Hurwitz table by equation the quadratic equation=0.
3. The characteristic equation of the control system is s5+15s4+85s3+225s2+274s+120=0 . What are the number of roots of the equation which lie to the left of the line s+1 = 0?
a) 2
b) 3
c) 4
d) 5
Answer
Answer: c [Reason:] The solution is obtained with the help of the Routh-Hurwitz table and in this the solution is obtained by equating the value as s-1 in the given equation.
4. The characteristic equation of a system is 2s5+s4+4s3+2s2+2s+1=0 . Which one of the following is correct?
a) Stable
b) Marginally stable
c) Unstable
d) Oscillatory
Answer
Answer: c [Reason:] The solution is obtained by using the Routh-Hurwitz table in which with the conventional method the number of sign changes are seen in the first row of the table and number of sign changes is equal to the number of the roots on the right half of s plane.
5. The characteristic equation of a control system is given by s5+s4+2s3+2s2+4s+6=0. The number of the roots of the equation which lie on the right half of s-plane:
a) 0
b) 1
c) 2
d) 3
Answer
Answer: c [Reason:] The solution is obtained by using the Routh-Hurwitz table in which with the conventional method the number of sign changes are seen in the first row of the table and number of sign changes is equal to the number of the roots on the right half of s plane.
6. Which of the following may result in instability problem?
a) Large error
b) High selectivity
c) High gain
d) Noise
Answer
Answer: c [Reason:] High gain results in instability problem and this is due to the low damping factor and damping factor is inversely proportional to the gain of the system.
7. For what values of K does the polynomial s4+8s3+24s2+32s+K=0 have roots with zero real parts?
a) 10
b) 20
c) 40
d) 80
Answer
Answer: d [Reason:] The solution is obtained by using the Routh-Hurwitz table and in which with the conventional method the number of sign changes are seen in the first row of the table and number of sign changes is equal to the number of the roots on the right half of s plane.
8. How many roots with positive real parts do the equation s3+s2-s+1=0 have?
a) 0
b) 1
c) 2
d) 3
Answer
Answer: c [Reason:] The roots with positive real parts are calculated with the help of the routh-hurwitz table and since the sign changes two times in first column therefore have two roots have positive parts.
9. Phase margin is always positive for stable feedback system?
a) True
b) False
Answer
Answer: a [Reason:] Phase margin is calculated at the gain cross over frequency at which the gain is 1 and this is calculated for stability and is always positive for stable feedback system.
10. In closed loop control system, what is the sensitivity of the gain of the overall system, M to the variation in G?
a) 1/1+GH
b) 1/1+G
c) G/1GH
d) G/1+G
Answer
Answer: a [Reason:] The sensitivity of the control system is defined as the change in the output to the change in the input and senstivity of the gain of the overall system, M to the variation in G is 1/1+GH.
