# 8 multiple choice ECET 345

1. (TCO 1) A signal that is a function of time has following properties or the following applies to it.(Points : 4)       it is impossible to change the properties of a signal.

A signal can be modified by a system which applies a transformation to it.

an electrical signal can only be transformed into an electrical signal.

an electrical signal can only be transformed into a non-electrical signal.

 Question 2. 2. (TCO 1) A sinusoidal signal, 4 sin(ωt), passing through an LTI system, undergoes a gain of 1.5 and a 45-degree phase lag. The resulting output signal will be mathematically described as(Points : 4)

5.5 sin(ωt).

6 sin(ωt – π/4).

6 sin(ωt + π/4).

5.5 sin(ωt – π/4).

 Question 3. 3. (TCO 1) Determine which of the following is a linear system by applying the principle of superposition. (Points : 4)

y = x2

y= 2 x + 2

y = 2x

 Question 4. 4. (TCO 1) A continuous time system has an output, y, which is given by . It is sampled at a frequency of 2 Hz. Determine the expression that correctly represents the discrete signal obtained after sampling and its value for n = 2. (Points : 4)

y(n) = , value at n = 2 is -1

y(n) = , value at n = 2 is 0.0174

y(n) = , value at n = 2 is 0

y(n) = , value at n = 2 is 0.841

 Question 5. 5. (TCO 1) A signal given by 5 Cos (20*pi*t) + 20 Sin (40*pi*t) is sampled at a rate of 15 Hz. Is the Nyquist theorem violated? (Points : 4)

No, it is not violated.

Yes, it is violated.

Insufficient data to answer the question

Question cannot be answered because sampling time is unknown

 Question 6. 6. (TCO 1) A continuous signal is described by 15 sin( 100t + pi/2). Its numerical value at t = 0 seconds is given by (Points : 4)

15.

pi/2.

100.

0.

 Question 7. 7. (TCO 1) A discrete time sequence is shown below in a figure. All values not shown can be assumed to be zero. Describe the sequence as a sum of undelayed (if any) and delayed step functions. (Points : 3)

– 2δ(n-1) – 2 δ(n-2) + δ (n-3) +δ (n-4)

δ(n-1) – 2 δ(n-2) – 2 δ (n-3) – δ (n-4)

-2δ(n) –  δ(n-1) –  δ (n-2) +  + δ(n-3)

δ(n-1) + 2 δ(n-2) + δ(n-3) +2 δ (n-4)

 Question 8. 8. (TCO 1)  A discrete time sequence is shown below in a figure. All values not shown can be assumed to be zero. Describe the sequence as a sum of undelayed (if any) and delayed step functions. (Points : 3)

2U(n) -4 U(n-1) + 3 U(n-2)

2U(n) -4 U(n-1) + 3 U(n-2) – U(n-3)

-2U(n) +4 U(n-1) + 3 U(n-2) – 3U(n-3)

2U(n) + 4 U(n-1) + 3 U(n-2) – 3U(n-3)

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