Quiznetik
Signals and Systems | Set 1
1. Evaluate the following function in terms of t: {integral from 0 to t}{Integral from -inf to inf}d(t)
A. 1⁄t
B. 1⁄t2
C. t
D. t2
Correct : C. t
2. The fundamental period of exp(jwt) is
A. pi/w
B. 2pi/w
C. 3pi/w
D. 4pi/w
Correct : B. 2pi/w
3. Find the magnitude of exp(jwt). Find the boundness of sin(t) and cos(t).
A. 1, [-1,2], [-1,2]
B. 0.5, [-1,1], [-1,1]
C. 1, [-1,1], [-1,2]
D. 1, [-1,1], [-1,1]
Correct : D. 1, [-1,1], [-1,1]
4. Find the value of {sum from -inf to inf} exp(jwn)*d[n].
A. 0
B. 1
C. 2
D. 3
Correct : B. 1
5. Compute d[n]d[n-1] + d[n-1]d[n-2] for n = 0, 1, 2.
A. 0, 1, 2
B. 0, 0, 1
C. 1, 0, 0
D. 0, 0, 0
Correct : D. 0, 0, 0
6. Defining u(t), r(t) and s(t) in their standard ways, are their derivatives defined at t = 0?
A. yes, yes, no
B. no, yes, no
C. no, no, yes
D. no, no, no
Correct : D. no, no, no
7. Which is the correct Euler expression?
A. exp(2jt) = cos(2t) + jsin(t)
B. exp(2jt) = cos(2t) + jsin(2t)
C. exp(2jt) = cos(2t) + sin(t)
D. exp(2jt) = jcos(2t) + jsin(t)
Correct : B. exp(2jt) = cos(2t) + jsin(2t)
8. The range for unit step function for u(t – a), is
A. t < a
B. t ≤ a
C. t = a
D. t ≥ a
Correct : D. t ≥ a
9. Which one of the following is not a ramp function?
A. r(t) = t when t ≥ 0
B. r(t) = 0 when t < 0
C. r(t) = ∫u(t)dt when t < 0
D. r(t) = du(t)⁄dt
Correct : D. r(t) = du(t)⁄dt
10. Unit Impulse function is obtained by using the limiting process on which among the following functions?
A. triangular function
B. rectangular function
C. signum function
D. sinc function
Correct : B. rectangular function
11. When is a complex exponential signal pure DC?
A. σ = 0 and Ω < 0
B. σ < 0 and Ω = 0
C. σ = 0 and Ω = 0
D. σ < 0 and Ω < 0
Correct : C. σ = 0 and Ω = 0
12. What is exp(ja) equal to, where j is the square root of unity?
A. cos ja + jsin a
B. sin a + jcos a
C. cos j + a sin j
D. cos a + jsin a
Correct : D. cos a + jsin a
13. What is the magnitude of exp(2+3j)?
A. exp(2.3)
B. exp(3)
C. exp(2)
D. exp(3/2)
Correct : C. exp(2)
14. What is the fundamental frequency of exp(2pi*w*j)?
A. 1pi*w
B. 2pi*w
C. w
D. 2w
Correct : C. w
15. Total energy possessed by a signal exp(jwt) is?
A. 2pi/w
B. pi/w
C. pi/2w
D. 2pi/3w
Correct : A. 2pi/w
16. Sinusoidal signals multiplied by decaying exponentials are referred to as
A. amplified sinusoids
B. neutralized sinusoids
C. buffered sinusoids
D. damped sinusoids
Correct : D. damped sinusoids
17. What is the period of exp(2+pi*j/4)t?
A. 4
B. 8
C. 16
D. 20
Correct : B. 8
18. exp(jwt) is periodic
A. for any w
B. for any t
C. for no w
D. for no t
Correct : A. for any w
19. Define the fundamental period of the following signal x[n] = exp(2pi*j*n/3) + exp(3*pi*j*n/4)?
A. 8
B. 12
C. 18
D. 24
Correct : D. 24
20. exp[jwn] is periodic
A. for any w
B. for any t
C. for w=2pi*m/n
D. for t = 1/w
Correct : C. for w=2pi*m/n
21. The most general form of complex exponential function is:
A. eσt
B. eΩt
C. est
D. eat
Correct : C. est
22. A complex exponential signal is a decaying exponential signal when
A. Ω = 0 and σ > 0
B. Ω = 0 and σ = 0
C. Ω ≠ 0 and σ < 0
D. Ω = 0 and σ < 0
Correct : D. Ω = 0 and σ < 0
23. When is a complex exponential signal sinusoidal?
A. σ =0 and Ω = 0
B. σ < 0 and Ω = 0
C. σ = 0 and Ω ≠ 0
D. σ ≠ 0 and Ω ≠ 0
Correct : C. σ = 0 and Ω ≠ 0
24. An exponentially growing sinusoidal signal is:
A. σ = 0 and Ω = 0
B. σ > 0 and Ω ≠ 0
C. σ < 0 and Ω ≠ 0
D. σ = 0 and Ω ≠ 0
Correct : B. σ > 0 and Ω ≠ 0
25. Determine the nature of the signal: x(t) = e-0.2t [cosΩt + jsinΩt].
A. exponentially decaying sinusoidal signal
B. exponentially growing sinusoidal signal
C. sinusoidal signal
D. exponential signal
Correct : A. exponentially decaying sinusoidal signal
26. A signal is a physical quantity which does not vary with
A. time
B. space
C. independent variables
D. dependent variables
Correct : D. dependent variables
27. Most of the signals found in nature are
A. continuous-time and discrete-time
B. continuous-time and digital
C. digital and analog
D. analog and continuous-time
Correct : D. analog and continuous-time
28. Which one of the following is not a characteristic of a deterministic signal?
A. exhibits no uncertainty
B. instantaneous value can be accurately predicted
C. exhibits uncertainty
D. can be represented by a mathematical equation
Correct : C. exhibits uncertainty
29. Sum of two periodic signals is a periodic signal when the ratio of their time periods is
A. a rational number
B. an irrational number
C. a complex number
D. an integer
Correct : A. a rational number
30. Determine the Time period of: x(t)=3 cos(20t+5)+sin(8t-3).
A. 1/10 sec
B. 1/20 sec
C. 2/5 sec d 2/4 sec
Correct : C. 2/5 sec d 2/4 sec
31. Determine the odd component of the signal: x(t)=cost+sint.
A. sint
B. 2sint
C. cost
D. 2cost
Correct : C. cost
32. Is the signal sin(t) anti-symmetric?
A. yes
B. no
Correct : A. yes
33. For an energy signal
A. e=0
B. p= ∞
C. e= ∞
D. p=0
Correct : D. p=0
34. Determine the power of the signal: x(t) = cos(t).
A. 1/2
B. 1
C. 3/2
D. 2
Correct : A. 1/2
35. Is the following signal an energy signal? x(t) = u(t) – u(t – 1)
A. yes
B. no
Correct : A. yes
36. A signal is anti-causal if
A. x(t) = 0 for t = 0
B. x(t) = 1 for t < 0
C. x(t) = 1 for t > 0
D. x(t) = 0 for t > 0
Correct : D. x(t) = 0 for t > 0
37. Is the signal x(t)= eat u(t) causal?
A. yes
B. no
Correct : A. yes
38. Is the signal x(n) = u(n + 4) – u(n – 4) causal?
A. yes
B. no
Correct : B. no
39. The type of systems which are characterized by input and the output capable of taking any value in a particular set of values are called as
A. analog
B. discrete
C. digital
D. continuous
Correct : D. continuous
40. An example of a discrete set of information/system is
A. the trajectory of the sun
B. data on a cd
C. universe time scale
D. movement of water through a pipe
Correct : B. data on a cd
41. A system which is linear is said to obey the rules of
A. scaling
B. additivity
C. both scaling and additivity
D. homogeneity
Correct : C. both scaling and additivity
42. A time invariant system is a system whose output
A. increases with a delay in input
B. decreases with a delay in input
C. remains same with a delay in input
D. vanishes with a delay in input
Correct : C. remains same with a delay in input
43. Should real time instruments like oscilloscopes be time invariant?
A. yes
B. sometimes
C. never
D. they have no relation with time variance
Correct : A. yes
44. All real time systems concerned with the concept of causality are
A. non causal
B. causal
C. neither causal nor non causal
D. memoryless
Correct : B. causal
45. A system is said to be defined as non causal, when
A. the output at the present depends on the input at an earlier time
B. the output at the present does not depend on the factor of time at all
C. the output at the present depends on the input at the current time
D. the output at the present depends on the input at a time instant in the future
Correct : D. the output at the present depends on the input at a time instant in the future
46. When we take up design of systems, ideally how do we define the stability of a system?
A. a system is stable, if a bounded input gives a bounded output, for some values of the input
B. a system is unstable, if a bounded input gives a bounded output, for all values of the input
C. a system is stable, if a bounded input gives a bounded output, for all values of the input
D. a system is unstable, if a bounded input gives a bounded output, for some values of the input
Correct : C. a system is stable, if a bounded input gives a bounded output, for all values of the input
47. All causal systems must have the component of
A. memory
B. time invariance
C. stability
D. linearity
Correct : A. memory
48. What are fourier coefficients?
A. the terms that are present in a fourier series
B. the terms that are obtained through fourier series
C. the terms which consist of the fourier series along with their sine or cosine values
D. the terms which are of resemblance to fourier transform in a fourier series are called fourier series coefficients
Correct : C. the terms which consist of the fourier series along with their sine or cosine values
49. Which are the fourier coefficients in the following?
A. a0, an and bn
B. an
C. bn
D. an and bn
Correct : A. a0, an and bn
50. Do exponential fourier series also have fourier coefficients to be evaluated.
A. true
B. false
Correct : A. true
51. The fourier series coefficients of the signal are carried from –T/2 to T/2.
A. true
B. false
Correct : A. true
52. What is the polar form of the fourier series?
A. x(t) = c0 + ∑cncos(nwt+ϕn)
B. x(t) = c0 + ∑cncos(ϕn)
C. x(t) = ∑cncos(nwt+ϕn)
D. x(t) = c0+ ∑cos(nwt+ϕn)
Correct : A. x(t) = c0 + ∑cncos(nwt+ϕn)
53. What is a line spectrum?
A. plot showing magnitudes of waveforms are called line spectrum
B. plot showing each of harmonic amplitudes in the wave is called line spectrum
C. plot showing each of harmonic amplitudes in the wave is called line spectrum
D. plot showing each of harmonic amplitudes called line spectrum
Correct : B. plot showing each of harmonic amplitudes in the wave is called line spectrum
54. Fourier series is not true in case of discrete time signals.
A. true
B. false
Correct : B. false
55. What is the disadvantage of exponential Fourier series?
A. it is tough to calculate
B. it is not easily visualized
C. it cannot be easily visualized as sinusoids
D. it is hard for manipulation
Correct : C. it cannot be easily visualized as sinusoids
56. Fourier series uses which domain representation of signals?
A. time domain representation
B. frequency domain representation
C. both combined
D. neither depends on the situation
Correct : B. frequency domain representation
57. How does Fourier series make it easier to represent periodic signals?
A. harmonically related
B. periodically related
C. sinusoidally related
D. exponentially related
Correct : A. harmonically related
58. Which of the following is correct regarding to impulse signal?
A. x[n]δ[n] = x[0]δ[n]
B. x[n]δ[n] = δ[n]
C. x[n]δ[n] = x[n]
D. x[n]δ[n] = x[0]
Correct : A. x[n]δ[n] = x[0]δ[n]
59. Weighted superposition of time-shifted impulse responses is termed as for discrete-time signals.
A. convolution integral
B. convolution multiple
C. convolution sum
D. convolution
Correct : C. convolution sum
60. Find the convolution sum of sequences x1[n] = (1, 2, 3) and x2[n] = (2, 1, 4).
A. {2, 5, 12, 11, 12}
B. {2, 12, 5, 11, 12}
C. {2, 11, 5, 12, 12}
D. {-2, 5,-12, 11, 12}
Correct : A. {2, 5, 12, 11, 12}
61. The Fourier series for the function f (x) = sin2x is
A. 0.5 + 0.5 sin 2x
B. 0.5 – 0.5 sin 2x
C. 0.5 + 0.5 cos 2x
D. 0.5 – 0.5 cos 2x
Correct : D. 0.5 – 0.5 cos 2x
62. The type of systems which are characterized by input and the output capable of taking any value in a particular set of values are called as
A. analog
B. discrete
C. digital
D. continuous
Correct : D. continuous
63. Then, y[k] = x[3k-2] is
A. y[k] = 1, for k = 0, 1 and 0 otherwise
B. y[k] = 1, for k = 1 and -1 for k=-1
C. y[k] = 1, for k = 0, 1 and -1 otherwise
D. y[k] = 1, for k = 0, 1 and 0 otherwise
Correct : A. y[k] = 1, for k = 0, 1 and 0 otherwise
64. The system described by the difference equation y(n) – 2y(n-1) + y(n-2) = X(n) – X(n-1) has y(n) = 0 and n<0. If x (n) = δ(n), then y (z) will be?
A. 2
B. 1
C. 0
D. -1
Correct : C. 0
65. A Discrete signal is said to be even or symmetric if X(-n) is equal to
A. x(n)
B. 0
C. –x(n)
D. –x(-n)
Correct : A. x(n)
66. Impulse response is the output of system due to impulse input applied at time=0?
A. linear
B. time varying
C. time invariant
D. linear and time invariant
Correct : D. linear and time invariant
67. For a causal L.T.I. system, the impulse response is 0 for
A. t<0
B. t=0
C. t>0
D. always
Correct : A. t<0
68. The convolution of a discrete signal with itself is
A. squaring the signal
B. doubling the signal
C. adding two signals
D. is not possible
Correct : A. squaring the signal
69. The convolution of a function with an impulse function delayed to an instant 3 in time results in
A. an advance in the function by 3 units in time
B. the function itself
C. a delay in the function by 3 units in time
D. cannot be determined
Correct : C. a delay in the function by 3 units in time
70. A continuous signal can be represented as the product of an impulse function and the signal itself.
A. true
B. false
Correct : A. true
71. What is the Scope value if the signal generator has a frequency of 2 Hz only?
A. an attenuated signal of same frequency
B. the entire signal at the same frequency
C. the entire signal at reduced frequency
D. an attenuated signal at reduced frequency
Correct : A. an attenuated signal of same frequency
72. If two LTI systems with impulse response h1 (t) and h2 (t) and are connected in parallel then output is given by
A. y(t) = x(t) *(h1(t) + h2(t))
B. y(t) = x(t) + (h1(t) + h2(t))
C. y(t) = x(t) * (h1(t) h2(t))
D. y(t) = (x(t) * h1(t)) + h2(t)
Correct : A. y(t) = x(t) *(h1(t) + h2(t))
73. When two LTI systems with impulse responses ha (t) and hb (t) are cascaded then equivalent response is given by
A. h(t) = ha(t) + hb(t)
B. h(t) = ha(t) – hb(t)
C. h(t) = ha(t) hb(t)
D. h(t) = ha(t) * hb(t)
Correct : D. h(t) = ha(t) * hb(t)
74. The condition for memory-less system is given by
A. h[k] = cδ[k]
B. h[k] = cδ[n-k]
C. h[k] = ch[k]δ[k]
D. h[k] = ch[n-k]δ[k]
Correct : A. h[k] = cδ[k]
75. The causal continuous system with impulse response should satisfy equation.
A. h(t)=0,t<0
B. h(t)=0,t>0
C. h(t)≠0,t<0
D. h(t)≠0,t≤0
Correct : A. h(t)=0,t<0
76. Causal systems are
A. anticipative
B. non anticipative
C. for certain cases anticipative
D. for certain cases anticipative and non anticipative
Correct : B. non anticipative
77. The impulse response of discrete-time signal is given by h [n] = u [n+3]. Whether the system is causal or not?
A. causal
B. non-causal
C. insufficient information
D. the system cannot be classified
Correct : B. non-causal