Digital Signal Processing Multiple Choice Questions on “Classification of Signals”.
1. Which of the following is done to convert a continuous time signal into discrete time signal?
A. Modulating
B. Sampling
C. Differentiating
D. Integrating
Answer: B
Clarification: A discrete time signal can be obtained from a continuous time signal by replacing t by nT, where T is the reciprocal of the sampling rate or time interval between the adjacent values. This procedure is known as sampling.
2. The deflection voltage of an oscilloscope is a ‘deterministic’ signal.
A. True
B. False
Answer: A
Clarification: The behavior of the signal is known and can be represented by a saw tooth wave form. So, the signal is deterministic.
3. The even part of a signal x(t) is?
A. x(t)+x(-t)
B. x(t)-x(-t)
C. (1/2)*(x(t)+x(-t))
D. (1/2)*(x(t)-x(-t))
Answer: C
Clarification: Let x(t)=xe(t)+xo(t)
=>x(-t)=xe(-t)-xo(-t)
By adding the above two equations, we get
xe(t)=(1/2)*(x(t)+x(-t)).
4. Which of the following is the odd component of the signal x(t)=e(jt)?
A. cost
B. j*sint
C. j*cost
D. sint
Answer: B
Clarification: Let x(t)=e(jt)
Now, xo(t)=(1/2)*(x(t)-x(-t))
=(1/2)*(e(jt) – e(-jt))
=(1/2)*(cost+jsint-cost+jsint)
=(1/2)*(2jsint)
=j*sint.
5. For a continuous time signal x(t) to be periodic with a period T, then x(t+mT) should be equal to ___________
A. x(-t)
B. x(mT)
C. x(mt)
D. x(t)
Answer: D
Clarification: If a signal x(t) is said to be periodic with period T, then x(t+mT)=x(t) for all t and any integer m.
6. Let x1(t) and x2(t) be periodic signals with fundamental periods T1 and T2 respectively. Which of the following must be a rational number for x(t)=x1(t)+x2(t) to be periodic?
A. T1+T2
B. T1-T2
C. T1/T2
D. T1*T2
Answer: C
Clarification: Let T be the period of the signal x(t)
=>x(t+T)=x1(t+mT1)+x2(t+nT2)
Thus, we must have
mT1=nT2=T
=>(T1/T2)=(k/m)= a rational number.
7. Let x1(t) and x2(t) be periodic signals with fundamental periods T1 and T2 respectively. Then the fundamental period of x(t)=x1(t)+x2(t) is?
A. LCM of T1 and T2
B. HCF of T1and T2
C. Product of T1 and T2
D. Ratio of T1 to T2
Answer: A
Clarification: For the sum of x1(t) and x2(t) to be periodic the ratio of their periods should be a rational number, then the fundamental period is the LCM of T1 and T2.
8. All energy signals will have an average power of ___________
A. Infinite
B. Zero
C. Positive
D. Cannot be calculated
Answer: B
Clarification: For any energy signal, the average power should be equal to 0 i.e., P=0.
9. x(t) or x(n) is defined to be an energy signal, if and only if the total energy content of the signal is a ___________
A. Finite quantity
B. Infinite
C. Zero
D. None of the mentioned
Answer: A
Clarification: The energy signal should have a total energy value that lies between 0 and infinity.
10. What is the period of cos2t+sin3t?
A. pi
B. 2*pi
C. 3*pi
D. 4*pi
Answer: B
Clarification: Period of cos2t=(2*pi)/2=pi
Period of sin3t=(2*pi)/3
LCM of pi and (2*pi)/3 is 2*pi.