# Multiple choice question for engineering

## Set 1

1. Consider the following statements regarding a linear discrete-time system:

H (z) = z^{2}+1/(z+0.5)(z-0.5)

1. The system is stable

2. The initial value of h(0) of the impulse response is -4

3. The steady-state output is zero for a sinusoidal discrete time input of frequency equal to one-fourth the sampling frequency

Which of these statements are correct?

a) 1,2 and 3

b) 1 and 2

c) 1 and 3

d) 2 and 3

### View Answer

2. The minimum number of delay elements required realizing a digital filter with transfer function

H (z) =

a) 2

b) 3

c) 4

d) 5

### View Answer

3. A system can be represented in the form of state equations as:

S (n+1) =A S (n) +B x (n)

Y (n) = C S (n) +D x (n)

Where, A, B, C, D are the matrices , S(n) is the state vector , x(n) is the input and y(n) is the output . The transfer function of the system.

H (z) =Y (z)/X (z) is given by:

a) A(ZI – B)^{-1} C + D

b) B(ZI – C)^{-1} D + A

c) C(ZI – A)^{-1} B + D

d) D(ZI – A)^{-1} C + B

### View Answer

4. Assertion (A): The signals a^{n}u(n) and a^{n}u(-n-1) have the same Z transform, z/(z-a)

Reason (R): the region of convergence of a^{n}u(n) is |z|>|a|, whereas the ROC for a^{n}u(-n-1) is |z|<|a|.

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

### View Answer

5. What is the number of roots of the polynomial F(z) = 4z^{3}-8z^{2}-z+2, lying outside the unit circle?

a) 0

b) 1

c) 2

d) 3

### View Answer

6. Assertion (A): The discrete time system described by y[n] =2x[n] +4x[n-1] is unstable

Reason (R): It has an impulse response with a finite number of non-zero samples

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

### View Answer

7. What is the z-transform of the signal x[n] = a^{n}u(n)?

a) X(z) =1/z-1

b) X(z) = 1/1-z

c) X(z) = z/z-a

d) X(z) = 1/z-a

### View Answer

8. Which one of the following rules determine the mapping of s-plane to z-plane?

a) Right side of the s-plane maps into outside of the unit circle in z-plane

b) Left half of s-plane maps into inside of the unit circle

c) Imaginary axis in s-plane maps into the circumference of the unit circle

d) All of the mentioned

### View Answer

9. Assertion (A): The z-transform of the output of the sampler is given by the series.

Reason (R): The relationship is the result of the application of z = e^{-sT}, where T stands for the time gap between the samples.

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

### View Answer

10. Convolution of two sequences X1[n] and X2[n] are represented by:

a) X1(z)*X2(z)

b) X1(z)X2(z)

c) X1(z)+X2(z)

d) X1(z)/X2(z)

### View Answer

## Set 2

1. The discrete-time signal x (n) = (-1)^{n} is periodic with fundamental period

a) 6

b) 4

c) 2

d) 0

### View Answer

2. The frequency of a continuous time signal x (t) changes on transformation from x (t) to x (α t), α > 0 by a factor

a) α

b) 1/α

c) α^{2}

d) α

### View Answer

3. Two sequences x1 (n) and x2 (n) are related by x2 (n) = x1 (- n). In the z- domain, their ROC’s are

a) The same

b) Reciprocal of each other

c) Negative of each other

d) Complements of each other

### View Answer

4. The ROC of z-transform of the discrete time sequence x(n) = is:

a) 1/3>|z|<1/2

b) |z|>1/2

c) |z|<1/3

d) 2>|z|<3

### View Answer

5. Which one of the following is the correct statement? The region of convergence of z-transform of x[n] consists of the values of z for which x[n] is:

a) Absolutely integrable

b) Absolutely summable

c) Unity

d) <1

### View Answer

^{-n}is absolutely summable.

6. The region of convergence of the z-transform of a unit step function is:

a) |z|>1

b) |z|<1

c) (Real part of z)>0

d) (Real part of z)<0

### View Answer

7. If the region of convergence of x1[n]+x2[n] is 1/>|z|<2/3, the region of convergence of x1[n]-x2[n] includes:

a) 1/3>|z|<3

b) 2/3>|z|<3

c) 3/2>|z|<3

d) 1/3>|z|<2/3

### View Answer

8. A sequence x (n) with the z-transform X (z) = Z^{4} + Z^{2} – 2z + 2 – 3Z^{-4} is applied to an input to a linear time invariant system with the impulse response h (n) = 2δ (n-3). The output at n = 4 will be:

a) -6

b) Zero

c) 2

d) -4

### View Answer

^{-3}Then taking the inverse Laplace transform of the equation of Y (z) at n=4 y(n) =0.

9. H (z) is discrete rational transfer function. To ensure that both H(z) and its inverse are stable:

a) Poles must be inside the unit circle and zeros must be outside the unit circle

b) Poles and zeroes must be inside the unit circle

c) Poles and zeroes must be outside the unit circle

d) Poles must be outside the unit circle and zeros must be inside the unit circle

### View Answer

10. Z and Laplace transform are related by:

a) s = ln z

b) s =ln z/T

c) s =z

d) s= T/ln z

### View Answer

^{st}s =ln z/T.

## Set 3

1. The DFT of a signal x(n) of length N is X(k). When X(k) is given and x(n) is computed from it, the length of x(n)

a) Is increased to infinity

b) Remains N

c) Becomes 2N – 1

d) Becomes N2

### View Answer

2. The system having input x (n) related to output y(n) as y (n) = log |x (n)| is:

a) Nonlinear, causal, stable

b) Linear, noncausal, stable

c) Nonlinear, causal, not stable

d) Linear, noncausal, not stable

### View Answer

3. Zero-order hold used in practical reconstruction of continuous-time signals is mathematically represented as a weighted-sum of rectangular pulses shifted by:

a) Any multiples of the sampling interval

b) Integer multiples of the sampling interval

c) One sampling interval

d) 1 second intervals

### View Answer

4. When two honest coins are simultaneously tossed, the probability of two heads on any given trial is:

a) 1

b) 3/4

c) 1/2

d) ¼

### View Answer

5. A continuous-time periodic signal x(t), having a period T, is convolved with itself. The resulting signal is

a) Not periodic

b) Periodic having a period T

c) Periodic having a period 2T

d) Periodic having a period T/2

### View Answer

6. If the Fourier series coefficients of a signal are periodic then the signal must be

a) Continuous-time, periodic

b) Discrete-time, periodic

c) Continuous-time, non-periodic

d) Discrete-time, non-periodic

### View Answer

7. The region of convergence of a causal finite duration discrete-time signal is

a) The entire z-plane except z = 0

b) The entire z-plane except z = ∞

c) The entire z-plane

d) A strip in z-plane enclosing jω–axis

### View Answer

8. The probability cumulative distribution function must be monotone and

a) Increasing

b) Decreasing

c) Non-increasing

d) Non-decreasing

### View Answer

9. Convolution is used to find:

a) The impulse response of an LTI System

b) Frequency response of a System

c) The time response of a LTI system

d) The phase response of a LTI system

### View Answer

10. The Fourier Transform of a rectangular pulse is

a) Another rectangular pulse

b) Triangular pulse

c) Sinc function

d) Impulse

### View Answer

## Set 4

1. The most important consideration for designing of control system are:

a) Transient response measures

b) Steady state error

c) Temporary response

d) Final response

### View Answer

2. Steady state error is usually specified in terms of :

a) Error constants

b) Damping factor

c) Speed of response

d) Bandwidth

### View Answer

3. Transient response measure is usually specified in terms of :

a) Error constants

b) Damping factor

c) Speed of response

d) Both b and c

### View Answer

4. In time domain the measure of relative stability is:

a) Damping factor

b) Maximum peak overshoot

c) Damping factor and Maximum peak overshoot

d) Speed of response

### View Answer

5. In frequency domain the measure of relative stability is:

a) Resonant peak

b) Phase margin

c) Resonant peak and phase margin

d) Maximum peak overshoot

### View Answer

6. In time domain the speed of response is measured in terms of :

a) Rise time

b) Settling time

c) Natural frequency

d) All of the mentioned

### View Answer

7. In frequency domain the speed of response is measured in terms of:

a) Resonant frequency

b) Bandwidth

c) Resonant peak and bandwidth

d) Maximum peak overshoot

### View Answer

8. The compensator for the system can be:

a) Electrical

b) Mechanical

c) Hydraulic

d) All of the mentioned

### View Answer

9. The compensator transfer function can be placed in:

a) Cascade or series compensation

b) Feedback or parallel compensation

c) Positive

d) Negative

### View Answer

10. Lead compensator speeds up the transient response and increases the margin of stability of a system.

a) True

b) False

### View Answer

## Set 5

1. If the speed of rotation of a separately excited dc machine is halved and the filed strength is also reduced to half of the original. Then the emf induced in the armature

a) reduces to 1/4th of original

b) reduces to half of original

c) remains same

d) doubles

### View Answer

2. If the speed of rotation for a four pole, 220V dc machine is 1 m/s, flux density as 2T having length of bore as 0.1m and radius of 0.5m.

The emf induced under pole faces will be

a) 0.2 V

b) 0.1 V

c) 0.2*pi V

d) 220 V

### View Answer

3. The induced emf in the armature of a 4-pole dc machine is

a) directly proportional to speed and field strength applied to it

b) directly proportional to speed

c) directly proportional to field strength applied to it

d) inversely proportional to speed and inversely proportional to field strength applied to it

### View Answer

4. If the armature current is by mistake increased to 50% for the dc machine,

a) then the induced emf remains unchanged

b) then the induced emf doubles

c) then the induced emf halves

d) none of the mentioned

### View Answer

5. For a four pole, 16 slot armature with two coil-side/slot having lap connected progressive winding has single turn coils. The same machine is then wave wound, the emf induced in the lap wound dc machine to that of wave wound will be

a) 2

b) 0.5

c) 1

d) 4

### View Answer

6. A duplex lap wound armature is used in six pole dc machine with six brush set. The number of current paths in this machine is

a) 12

b) 6

c) 3

d) 2

### View Answer

7. For a four pole, 16 slot armature with two coil-side/slot having wave connected progressive winding has single turn coils has simplex winding.

The number of current paths

a) 2

b) 6

c) 3

d) 4

### View Answer

8. For a four pole, 200 V dc shunt generator having armature resistance of 1 ohms. The current flowing in the armature is 10 A. What is the back emf generated if the terminal voltage of 220 V supply is fed?

a) 230 Volts

b) 210 Volts

c) 190 Volts

d) 200 Volts

### View Answer

9. For a 4 pole 200 V, 20 A dc generator running at the rated rpm with no load will be

a) zero no load losses

b) 4000 W no load losses

c) negligible no load losses

d) none of the mentioned

### View Answer

10. Which of the following cannot reduce the terminal voltage of a dc shunt generator?

a) Commutation

b) Armature reaction

c) Armature ohmic losses

d) Any of the mentioned

### View Answer

11. The emf vs speed characteristics of a dc generator is

a)

b)

c)

d)