SIGNALS & SYSTEMS

UNIT-1

1. Which signal is continuous function of an independent variable? level-1

(a) Analog (b) Digital (c) Discrete

2. Which signal can be represented by a rotating vector in a complex plane? level-2

(a) Complex Exponential (b) Exponential (c) Complex

3. Which of the following is a periodic signal? level-1

(a) x(t)= Au(t) (b) x(t)= Ae-jbt (c) x(t)= Aebt (d). x(t)= At

4. Which of the following statement is false? level-1

(a) Product of two odd signal is an odd signal

(b). Product of two even signal is an even signal

(c ) Product of odd & even signal is even signal

(d) Product of odd & even signal is odd signal.

5. Which signal is casual? level-1

(a) x(t)=A (b) x(t)=t (c) x(t)=u(t) (d)x(t)= eat

6. Which of the following statement is true? level-2

(i) Periodic signals are power signals

(ii) Non Periodic signals are energysignals

(iii) For energy signals power is zero

(iv) For power signals energy is zero

(a).i only (b) i & iionly (c) i & iii only (d) All the above

7. What about the stability of system in level-3

(a) system is stable

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(b) unstable

(c ) stable at 0.4

(d) Cant say

8.

8.

9.8. Which one is most appropriate dynamic system? level-2

(a) y(n) + y(n - 1) + y(n + 1)

(b) y(n) + y(n - 1)

(c) y(n) = x(n)

(d) y(n) + y(n - 1) + y(n + 3) = 0

9. The unit step response of a system starting from rest is given by c(t) = 1 - e-2t for t ≥ 0. The

transfer function of the system is level-2

(a)

( b ).

( c)

(d)

10. check the following system for causality level-2

1. y[n] = x[n] + 2x[n - 1]

2. y[n] = x[n - k]

3. y[n] = x[2n]

(a) (1) and (2)

(b) (2) and (3)

(c) (1) only

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(d) (1) and (3)

12. Which one of following is correct condition to check the stability of system? level-1

(a) Bounded I/P unbounded O/P

(b) Bounded I/P and O/P

(c) Bounded O/P and I/P

(d) Bounded I/P Bounded O/P

13 . An impulse train is level-2

(a) a number of pulses

(b) a number of pulses spaced from each other

(c) a number of pulses all originating together

(d) none of the above

14. The differentiation of unit step signal is, level-1

(a) Ramp signal (B) Impulse signal (c) Exponential signal (d) Parabolic signal.

15. Integral of unit impulse signal is level-1

(a) Infinity (b) Zero (c) One (d) Constant

16. Which of the following response of LTi system does not depend on initial condition? level-3

(a) Natural response (b) Free response (c) Forced response (d) Total response

17 Which system is casual system? level-2

(a) y(t)=x( t2) (b) y(t)=x2(t) (c ) y(t)=x(-t) (d) y(t)=x(2t)

18. Which system is stable system? level-2

(a) y(t)=tx(t) (b) y(t)=t2x(t) (c ) y(t)=etx(t) (d) y(t)= e-t x(t)

19.Which of the following impulse response of LTI system represents a stable system? level-3

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(a).h(t)= et cos u(t) (b) h(t)= et sin u(t) (c ) h(t)= e-t cos u(t) (d). h(t)= t sint u(t)

20. If h1(t) and h2(t) are impulse response of stable system in cascade then overall impulse response is

(a) .h1(t)* h2(t) (b) .h1(t) h2(t) (c ). h1(t)+ h2(t) (d) .h1(t)- h2(t)

level-3

Answers to the Objective Type Questions

UNIT-1

Q.no 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Answers a a b a c c a a b c a b b b c c b d c a

Levels 1 2 1 1 1 2 3 2 2 2 1 1 2 1 1 3 2 2 3 3

UNIT-II

ANALYSIS OF CONTINUOUS TIME SIGNALS

1. Fourier series applies to level-1

(a) Only Periodic Signals (c) only aperiodic signals

(b) both aperiodic and periodic signals (d) only random signals

2. The net areas of sinusoids over complete periods are level-1

(a) finite (b) infinite (c) Zero (d) none of these

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3. The trigonometric Fourier Series representation of a function with half wave Symmetry

consists of level-2

(a) Cosine Terms only (c) Odd harmonics

(b) sine terms only (d) Even harmonics

4. The Frequency Spectrum of a periodic signal is level-1

(a) Continuous (c) both continuous and discrete

(b) discrete (d) none of the above

5. The time domain representation of a signal graphically is called level-1

(a) waveform (b) spectrum (c) magnitude (d) Phase

6. In the Trignometric Fourier series representation of a signal, a0(or A0) is the level-1

(a) RMS value (c) Peak value

(b) Average value (d) Mean square value

7. An Exponential Fourier Series has level-2

(a) A one sided spectrum (c) both one sided and Two sided Spectrum

(b) A two sided Spectrum (d) none of the above

8. In the Frequency Spectrum of an Aperiodic signal, the spacing among the components is level-1

(a) large (b) small (c) Infinity (d) Zero

9. The Fourier Transform of DC signal x(t)=A is level-2

(a) AΩ (b) A2ΠΩ (c)A2Πδ(Ω) (d)A2Π

10. The Fourier Transform of rect (t/τ) is level-2

(a) τ/2 sinc Ωτ/2 (b) τ sin Ωτ/2 (c) τ/2 sinc2 Ωτ/4 (d) τ sinc2 Ωτ/2

11. The Fourier Transform of X(at) is level-1

(a) 1/|a| X(Ω/a) (b) 1/|a| X(aΩ) (c) 1/|a| X(a/Ω) (d) 1/| Ω | X(Ω/a)

12. Parsevals Identity States that = level-1

(a) (c) 1/2Π

(b) 1/2Π (d) 1/2Π

13. The Signum function X(t) can be written as level-3

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(a) u(t)-1 (b) 2u(t)-1 (c) 1-u(t) (d) u(t)+u(-t)

14. The Laplace Transform of eat cos(bt) is equal to level-2

(a) s+a /(s+a)2+b2 (b) s-a/( s-a)2+ b2 (c) s-a/( s+a)2+ b2 (d) (s+a) /(s-b)2

15. If L[f(t)]=F(s) then L[f(t-T)] is equal to level-3

(a) estF(s) (b) e-stF(s) (c) F(s)/1+esT (d)F(s)/1+e-sT

16. The function f(t) shown in the given figure will have a laplace transform as level-3

f(t)

1.0 ----------

0 1 2 t

(a) (c)

(b) (d)

17. If δ(t) denotes a unit impulse ,then the Laplace transform of will be level-2

(a) 1 (b) s2 (c) s (d) s-2

18. The following table lists some of the time functions and their Laplace transforms level-1

f(t) F(s)

δ(t) s

u(t) 1/s

tu(t) 2/s2

t2 u(t) 2/s3

of these, the correctly matched pair is

(a) 2 and 4 (b) 1 and 4 (c) 3 and 4 (d) 1 and 2

19. If x(t) and its first derivative are Laplace Transformable and the Laplace Transform

of x(t) is X(s),then lim X 0 x(t) is given by level-3

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(a) lim s sX(s) (b) lim s sX(s) (c) lim s (d) lim s

20. The final value of L-1 is level-2

(a) (b) 2 (c) 1 (d) 0

Answers to the Objective Type Questions

UNIT-2

Q.no 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Answers a c c b a b b d c b a c b b b d b a a c

Levels 1 1 2 1 1 1 2 1 2 2 1 1 3 2 3 3 2 1 3 2

UNIT-III LTI Continuous Time systems

1. The Fourier transform of the exponential signal j_ t e 0 is level-1(A) a constant. (B) a rectangular gate.(C) an impulse.

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(D) a series of impulses.

2. The Fourier transform (FT) of a function x (t) is X (f). The FT of dx(t )/ dt will be level-1(A) dX(f )/ df . (B) j2лf X(f ).(C) jf X(f ). (D) X(f )/(jf ).

3. The FT of a rectangular pulse existing between t = − T / 2 to t = T / 2 is a level-2(A) sinc squared function. (B) sinc function.(C) sine squared function. (D) sine function.

4. A given system is characterized by the differential equation:d2y(t)/dt2 – dy(t)/dt-2y(t)=x(t). The system is: (A) linear and unstable. level-1(B) linear and stable.(C) nonlinear and unstable. (D) nonlinear and stable.

5. The continuous time system described by y(t) = x (t2) is level-2(A) causal, linear and time varying.(B) causal, non-linear and time varying.(C) non causal, non-linear and time-invariant.(D) non causal, linear and time-invariant

6. The Laplace transform of u(t) is A(s) and the Fourier transform of u(t) is B(jw).Then level-1(A) 1/s and 1/jw(B) 2/s(C) 1/s and jw(D) 1/jw and 1/s

7. The impulse response of a system described by the differential equation d2y(t)/dt2 +y(t)=x(t)(A) a constant. (B) an impulse function.. level-2(C) a sinusoid. (D) an exponentially decaying function.

8 . The order of a linear constant-coefficient differential equation representing a system refers to the number of(A) active devices. level-2(B) elements including sources.(C) passive devices. (D) none of those.

9. Region of convergence of a causal LTI system level-1

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(A) is the entire s-plane. (B) is the right-half of s-plane.(C) is the left-half of s-plane. (D) does not exist.

10. The system having input x(n) related to output y(n) as y(n) = log10 x(n) is: level-1(A) nonlinear, causal, stable. (B) linear, noncausal, stable.(C) nonlinear, causal, not stable. (D) linear, noncausal, not stable.

11 Convolution is used to find: level-1(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

12. The Fourier Transform of a rectangular pulse is level-2(A) Another rectangular pulse (B) Triangular pulse(C) Sinc function (D) Impulse.

13. The property of Fourier Transform which states that the compression in time domain is equivalent to expansion in the frequency domain is(A) Duality. level-1(B) Scaling.(C) Time Scaling. (D) Frequency Shifting.

14. The function which has its Fourier transform, Laplace transform, and Z transform unity is(A) Gausian level-1(B) impulse(C) Sinc (D) pulse

15. The autocorrelation of a rectangular pulse is level-2(A) another rectangle pulse (B) Square pulse(C) Triangular pulse (D) Sinc pulse16. If the Fourier series coefficients of a signal are periodic then the signal must be level-2(A) continuous-time, periodic (B) discrete-time, periodic(C) continuous-time, non periodic (D) discrete-time, non periodic

17. A transmission is said to be _____________ if the response of the system is exact replica of the input signal. level-2

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(A) LTI (B) Distorted(C) Distortionless (D) Causal

18. The autocorrelation of a sinusoid is level-2(A) Sinc pulse (B) another sinusoid(C) Rectangular pulse (D) Triangular pulse

19. The Fourier transform of impulse function is level-1(A) d(w) (B) 2pw(C) 1 (D) sinc f

20 .The spectral density of white noise is level-2(A) Exponential (B) Uniform(C) Poisson (D) Gaussian

Q.no 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Answers c b b a d a c d b a c c b b c b c b c b

Levels 1 1 2 1 2 1 2 2 1 1 1 2 1 1 2 2 2 2 1 2

LEVELS CREDITS

1 Easy

2 Moderate

3 Difficult

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