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Multiple choice question for engineering

Set 1

1. Statement (I): Aliasing occurs when the sampling frequency is less than twice the maximum frequency in the signal.
Statement (II): Aliasing is a reversible process.
a) Both statement (I) and Statement (II) are individually true and Statement (II) is the correct explanation of Statement (I).
b) Both Statement (I) and Statement (II) are individually true but Statement (II) is not correct explanation of Statement (I)
c) Statement (I) is true but Statement (II) is false
d) Statement (I) is False but Statement (II) is true

View Answer

Answer: c [Reason:] Aliasing is an irreversible process. Once aliasing has occurred then signal can-not be recovered back.

2. A band limited signal with a maximum frequency of 5 KHz to be sampled. According to the sampling theorem, the sampling frequency which is not valid is:
a) 5 KHz
b) 12 KHz
c) 15 KHz
d) 20 KHz

View Answer

Answer: a [Reason:] fs (min) =2fm fs (min) =2*5 =10 KHz So, fs >=1o KHz.

3. Let x(t) be a continuous-time, real valued signal band-limited to F Hz. The Nyquist sampling rate in Hz, For y(t) =x(0.5t) +x(t)-x(2t) is
a) F
b) 2F
c) 4F
d) 8F

View Answer

Answer: c [Reason:] Expansion in time domain in compression in frequency domain and vice-versa. So, the maximum frequency component in given signal is 2F Hz. And according to sampling theorem. Nyquist rate =2fm =4F Hz.

4. Increased pulse-width in the flat-top sampling leads to:
a) Attenuation of high frequencies in reproduction
b) Attenuation of low frequencies in reproduction
c) Greater aliasing errors in reproduction
d) No harmful effects in reproduction

View Answer

Answer: a [Reason:] As pulse width is increased, the width of the first lobe of the spectrum is decreased. Hence, increased pulse-width in the flat-top sampling, leads to attenuation of high frequencies in reproduction.

5. A bandpass sampling extends from 4-6 kHz. What is the smallest sampling frequency required to retain all the information in the signal.
a) 1 kHz
b) 2 kHz
c) 3 kHz
d) 4 kHz

View Answer

Answer: d [Reason:] fh =6 kHz Bandwidth = 2 kHz Fs =4 kHz.

6. A signal represented by x(t) =5cos 400πt is sampled at a rate 300 samples/sec. The resulting samples are passed through an ideal low pass filter of cut-off frequency 150 Hz. Which of the following will be contained in the output of the LPF?
a) 100 Hz
b) 100 Hz, 150 Hz
c) 50 Hz, 100 Hz
d) 50 Hz, 100 Hz, 150 Hz

View Answer

Answer: a [Reason:] x (t) =5cos400πt fm =200 Hz The output of the LPF will contain frequencies which are less than fc =150 Hz. So, fs-fm =300-200 =100 Hz is the only component present in the output of LPF.

7. A signal m(t) with bandwidth 500 Hz is first multiplied by a signal g(t). The resulting signal is passed through an ideal low pass filter with bandwidth 1 kHz. The output of the low pass filter would be :
a) Impulse
b) m(t)
c) 0
d) m(t)del(t)

View Answer

Answer: c [Reason:] m (t) g (t)->M (f)*G (f) After low pass filtering with fc =1 kHz, hence the output is zero.

8. An LTI system having transfer function s2+1/s2+2s+1 and input x(t) =sin(t+1) is in steady state. The output is sampled at ws rad/s to obtain the final output {y (k)}. Which of the following is true?
a) Y is zero for all sampling frequencies ws
b) Y is non zero for all sampling frequencies ws
c) Y is non zero for ws>2 but zero for ws<2
d) Y is zero for ws>2 but non zero for ws<2

View Answer

Answer: a [Reason:] x (t) =sin (t+1) w = 1 rad/s X(s) = es/s2+1 Y(s) = es/s2+2s+1 Y (∞) =0.

9. A digital measuring instrument employs a sampling rate of 100 samples/second. The sampled input x(n) is averaged using the difference equation:
Y (n) =[x (n)+x (n-1)+x(n-2)+x(n-4)/4]
For a step input, the maximum time taken for the output to reach the final value after the input transition is
a) 20 ms
b) 40 ms
c) 80 ms
d) ∞

View Answer

Answer: b [Reason:] Since output y depends on input, such as no delay, delay by 1 unit, and delay by 2 unit, delay by 4 unit, so it will sum all the samples after 4 Ts (maximum delay), to get one sample of y[n]. T =40 msec.

10. The sinusoid x(t) =6cos10πt is sampled at the rate of 15 Hz and applied to ideal rectangular LPF with cut-off frequency of 10 Hz, then the output of filter contains:
a) Only 10π rad/sec component
b) 10π rad/sec component
c) 10π rad/sec and 20π rad/sec components
d) +10π rad/sec and +20π rad/sec components

View Answer

Answer: b [Reason:] Output filter is the device that is used to filter some frequencies and make some frequencies in the response and in this case it contains 10π rad/sec.

Set 2

1. First column elements of the Routh’s tabulation are 3, 5, -3/4, ½, 2. It means that there are:
a) Is one root in the left half of s-plane
b) Are two roots in the left half of s-plane
c) Are two roots in the right half of the s-plane
d) Is one root in the right half of s-plane

View Answer

Answer: c [Reason:] Routh hurwitz criteria is used to find the stability of the system and this is determined by the number of roots in which the number of roots is equal to the number of sign changes.

2. Assertion (A): Feedback control system offer more accurate control over open-loop systems.
Reason (R): The feedback path establishes a link for input and output comparison and subsequent error correction.
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

View Answer

Answer: a [Reason:] Feedback control system offers more accuracy and also reduces the gain of the system and establishes the link for input and output comparison and subsequent error correction.

3. Consider the following statements:
a) The effect of feedback is to reduce the system error
b) Feedback increases the gain of the system in one frequency range but decreases in the other
c) Feedback can cause a system originally stable to become unstable
d) Both a and c

View Answer

Answer: d [Reason:] Feedback reduces error and can cause stable system to become unstable and also can make unstable system stable.

4. The Routh-Hurwitz criterion cannot be applied when the characteristic equation of the system contains any coefficients which is :
a) Negative real and exponential function
b) Negative real, both exponential and sinusoidal function of s
c) Both exponential and sinusoidal function of s
d) Complex, both exponential and sinusoidal function of s

View Answer

Answer: b [Reason:] The Routh-Hurwitz criterion cannot be applied when the characteristic equation of the system contains any coefficients which is negative real, both exponential and sinusoidal function of s.

5. The following characteristic equation results in stable operation of the feedback system s3+4s2+10s+11=0
a) True
b) False

View Answer

Answer: a [Reason:] Stable operation can be checked using the Routh-Hurwitz criterion where the first row of the the table is checked and with that.

6. Consider the following statements:
Routh-Hurwitz criterion gives:
1. Absolute stability
2. The number of roots lying on the right half of the s-plane
3. The gain margin and the phase margin
a) 1,2 and3
b) 1 and 2
c) 2 and 3
d) 1 and 3

View Answer

Answer: b [Reason:] Routh-Hurwitz criterion gives absolute stability and number of roots lying on the right half of the s-plane.

7. The given characteristic equation s4+s3+2s2+2s+3=0 has:
a) Zero root in the s-plane
b) One root in the RHS of s-plane
c) Two root in the RHS of s-plane
d) Three root in the RHS of s-plane

View Answer

Answer: c [Reason:] The stability analysis is done using Routh-Hurwitz criterion and hence the number of roots on the right is calculated.

8. Which of the following techniques is utilized to determine at the actual point at which the root locus crosses the imaginary axis?
a) Nyquist technique
b) Routh-Hurwitz technique
c) Nichol’s technique
d) Bode technique

View Answer

Answer: b [Reason:] Routh-Hurwitz technique is utilized to determine at the actual point at which the root locus crosses the imaginary axis.

9. The characteristic equation of a control system is given by s6+2s5+8s4+12s3+20s2+16s+16=0 . The number of the roots of the equation which lie on the imaginary axis of s-plane:
a) 0
b) 2
c) 4
d) 6

View Answer

Answer: c [Reason:] The stability analysis is done using Routh-Hurwitz criterion and hence the number of roots on the right is calculated.

10. Assertion (A): A linear, negative feedback control system is invariable stable if its open loop configuration is stable
Reason (R): the negative feedback reduces the overall gain of the feedback.
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

View Answer

Answer: d [Reason:] A linear, negative feedback control system is not necessarily stable if its open loop configuration is stable.

Set 3

1. The characteristic equation of a feedback control system is given bys3+5s2+(K+6)s+K=0. In the root loci diagram, the asymptotes of the root loci for large K meet at a point in the s plane whose coordinates are:
a) (2,0)
b) (-1,0)
c) (-2,0)
d) (-3,0)

View Answer

Answer: c [Reason:] The point is calculated by using Routh Hurwitz table and then equating the S0 term equal to zero.

2. The root locus diagram has loop transfer function G(s)H(s) = K/ s(s+4)(s2+4s+5) has
a) No breakaway points
b) Three real breakaway points
c) Only one breakaway points
d) One real and two complex breakaway points

View Answer

Answer: b [Reason:] The breakaway points are the points where the root locus branches break and it is not necessary that this point must lie on the root locus calculated by differentiating the value of K with respect to s and equating it with zero.

3. For asymptotes passing from breakaway point then this point is also centroid
a) True
b) False

View Answer

Answer: True [Reason:] Asymptotes are the lines of infinite length and these are tangents to the root locus that meet at infinity and for these, passing from breakaway point then this point is also centroid.

4. Transportation lag is seen in systems:
a) Amount to be transferred in large
b) Time take to transfer is large
c) Inefficiency of the process
d) Errors

View Answer

Answer: b [Reason:] Transportation lag is the delay that is seen in the systems where the output is not following the input and is seen in systems where the time taken to transfer is very large.

5. Mediums responsible for transportation lag are:
a) Lines
b) Pipes
c) Belt conveyors
d) All of the mentioned

View Answer

Answer: d [Reason:] Transportation lag is the delay that is seen in the systems where the output is not following the input and is mainly seen in the practical mediums where the time of transfer is very large.

6. Linear lumped parameter models are not valid under situations as:
a) Transmission pipe between the hydraulic pump and the motor causes a time lag in transportation of oil from pump to motor
b) Transmission of heat by conduction or convection produces serious transportation lag
c) Transmission pipe causes the time lag and loss of heat by conduction and convection
d) Transmission of pipe causes neither any time lag nor any heat loss

View Answer

Answer: c [Reason:] Linear lumped parameter models are the models that simplifies the description of the behaviour of spatially distributed physical systems into a topology consisting of discrete systems and not valid when the pure time lags are negligible compared to other lags in the system.

7. Practically all the systems have transportation lag :
a) True
b) False

View Answer

Answer: b [Reason:] Not all systems have transportation lag but whose transmission time is more.

8. Transportation lag causes :
a) Instability in system
b) Stability in system
c) System remains unaffected
d) Bandwidth increases

View Answer

Answer: a [Reason:] Transportation lag is the delay that is seen in the systems where the output is not following the input and causes instability in the system.

9. The polar plot of a transfer function passes through the critical point (-1,0).Gain margin is
a) zero
b) -1dB
c) 1dB
d) Infinity

View Answer

Answer: a [Reason:] Gain margin is the point where the at phase cross over frequency gain of the system i 1 dB and of a polar plot passing through the critical point is zero.

10. Consider the following statements:
1. The effect of feedback is to reduce the system error
2. Feedback increases the gain of the system in one frequency range but decreases in another.
3. Feedback can cause a system that is originally stable to become unstable
Which of these statements are correct.
a) 1,2 and 3
b) 1 and 2
c) 2 and 3
d) 1 and 3

View Answer

Answer: c [Reason:] Feedback can be of two types as positive and negative and cause the increase in gain and also can cause stable system to become unstable.

Set 4

1. Stability of a system implies that :
a) Small changes in the system input does not result in large change in system output
b) Small changes in the system parameters does not result in large change in system output
c) Small changes in the initial conditions does not result in large change in system output
d) Small changes in the initial conditions result in large change in system output

View Answer

Answer: a [Reason:] Stability of the system implies that small changes in the system input, initial conditions, and system parameters does not result in large change in system output.

2. A linear time invariant system is stable if :
a) System in excited by the bounded input, the output is also bounded
b) In the absence of input output tends zero
c) Both a and b
d) None of the mentioned

View Answer

Answer: c [Reason:] A system is stable only if it is BIBO stable and asymptotic stable.

3. Asymptotic stability is concerned with :
a) A system under influence of input
b) A system not under influence of input
c) A system under influence of output
d) A system not under influence of output

View Answer

Answer: b [Reason:] Asymptotic stability concerns a free system relative to its transient behavior.

4. Bounded input and Bounded output stability notion concerns with :
a) A system under influence of input
b) A system not under influence of input
c) A system under influence of output
d) A system not under influence of output

View Answer

Answer: a [Reason:] BIBO stability concerns with the system that has input present.

5. If a system is given unbounded input then the system is:
a) Stable
b) Unstable
c) Not defined
d) Linear

View Answer

Answer: c [Reason:] If the system is given with the unbounded input then nothing can be clarified for the stability of the system.

6. Linear mathematical model applies to :
a) Linear systems
b) Stable systems
c) Unstable systems
d) All of the mentioned

View Answer

Answer: b [Reason:] As the output exceeds certain magnitude then the linear mathematical model no longer applies.

7. For non-linear systems stability cannot be determined due to:
a) Possible existence of multiple equilibrium states
b) No correspondence between bounded input and bounded output stability and asymptotic stability
c) Output may be bounded for the particular bounded input but may not be bounded for the bounded inputs
d) All of the mentioned

View Answer

Answer: d [Reason:] For non-linear systems stability cannot be determined as asymptotic stability and BIBO stability concepts cannot be applied, existence of multiple states and unbounded output for many bounded inputs.

8. If the impulse response in absolutely integrable then the system is :
a) Absolutely stable
b) Unstable
c) Linear
d) None of the mentioned

View Answer

Answer: a [Reason:] The impulse response must be absolutely integrable for the system to absolutely stable.

9. The roots of the transfer function do not have any effect on the stability of the system.
a) True
b) False

View Answer

Answer: b [Reason:] The roots of transfer function also determine the stability of system as they may be real, complex and may have multiplicity of various order.

10. Roots with higher multiplicity on the imaginary axis makes the system :
a) Absolutely stable
b) Unstable
c) Linear
d) None of the mentioned

View Answer

Answer: b [Reason:] Repetitive roots on the imaginary axis makes the system unstable.

Set 5

1. In a control system integral error compensation _______steady state error
a) Increases
b) Minimizes
c) Does not have any effect on steady state error
d) All of the mentioned

View Answer

Answer: b [Reason:] Integral compensation is the phase lag compensation as it reduces or minimizes the steady state error by not affecting the damping factor but reducing the natural frequency.

2. With feedback _____ reduces.
a) System stability
b) System gain
c) System stability and gain
d) Damping

View Answer

Answer: b [Reason:] With feedback damping increases and system gain reduces as they are inversely proportional to each other and for the good control system the speed of response must be high with low gain and oscillations.

3. An amplidyne can give which of the following characteristics?
a) Constant current
b) Constant voltage
c) Constant current as well as constant voltage
d) Constant current, constant voltage and constant power

View Answer

Answer: d [Reason:] An amplidyne is the device so constructed so as can give constant current, voltage and power and it is the important device as single device can achieve all these features.

4. Which of the following cannot be measured by LVDT?
a) Displacement
b) Velocity
c) Acceleration
d) Pressure

View Answer

Answer: d [Reason:] LVDT is the linear variable differential transformer and it is an inductive transformer and can measure displacement, velocity and acceleration but pressure cannot be measured by using LVDT.

5. __________directly converts temperature into voltage.
a) Thermocouple
b) Potentiometer
c) Gear train
d) LVDT

View Answer

Answer: a [Reason:] Among all the instruments Thermocouple is the instrument that has two different metals with different temperatures and the difference in temperature is converted into the potential difference.

6. The transfer function technique is considered as inadequate under which of the following conditions?
a) Systems having complexities and nonlinearities
b) Systems having stability problems
c) Systems having multiple input disturbances
d) All of the mentioned

View Answer

Answer: d [Reason:] State variable analysis is used as Transfer function approach cannot be practically used in the systems having complexities, nonlinearities, stability problems and multiple input.

7. Which of the following is the output of a thermocouple?
a) Alternating current
b) Direct current
c) A.C. voltage
d) D.C. voltage

View Answer

Answer: d [Reason:] Thermocouple is the instrument that has two different metals with different temperatures and the difference in temperature is converted into the potential difference and gives output in D.C. Voltage.

8. A.C. servomotor is basically a
a) Universal motor
b) Single phase induction motor
c) Two phase induction motor
d) Three phase induction motor

View Answer

Answer: c [Reason:] A.C. Servomotor is the servomotor in which the input is mainly the alternating current and is basically two phase induction motor.

9. The first order control system, which is well designed, has a
a) Small bandwidth
b) Negative time constant
c) Large negative transfer function pole
d) None of the mentioned

View Answer

Answer: c [Reason:] The first order control system which is the system with maximum one root which can be at origin and has well designed large negative transfer function pole.

10. Which of the following is exhibited by Root locus diagrams?
a) The poles of the transfer function for a set of parameter values
b) The bandwidth of the system
c) The response of a system to a step input
d) The frequency response of a system

View Answer

Answer: a [Reason:] Root locus diagrams is constructed by the locus traced by the gain of the system with the varying frequency and have the poles of the transfer function for a set of parameter values.