Viva Questions on Signals
Viva Questions on Signals, Introduction to signals viva questions, Short Questions on Signals, continuous-time signal viva questions, discrete-time Signals viva questions, digital signal viva questions, Electronics Viva Questions, Signal & Systems Viva Questions.
Short Questions and Answers
Q.1. Define a signal.
Ans. A signal is defined as any physical quantity that varies with time, space, or any other independent variable.
Q.2. Define deterministic and random signals.
Ans.
Deterministic Signal: A deterministic signal is a signal exhibiting no uncertainty of its value at all instants. Its instantaneous value can be accurately predicted by specifying a mathematical relation.
Random Signal: A random signal is a signal characterized by uncertainty before its actual occurrence. (or) A random signal can not be predicted before its actual occurrence.
Q.3. Define step function and Delta function.
Ans. A step function is defined as
x(t)=\begin{cases}A & \text{ for } t\geqslant 0 \\0 & \text{ for } t< 0 \end{cases}A delta function is defined as
\int_{-\infty }^{\infty }\delta (t)dt=1and δ(t) = 0 for t ≠ 0.
Q.4. Define periodic and aperiodic signals.
Ans. A signal x(t) is periodic with period T if and only if
x(t + T) = x(t) for all t
If there is no value of T that satisfies the above equation the signal is called aperiodic.
Q.5. Define symmetric and antisymmetric signals.
Ans. A real valued signal x(t) is called symmetric if
x(-t) = x(t)
on the otherhand, a signal x(t) is called antisymmetric if
x(-1) = – x(t)
Q.6. Define energy and power signals.
Ans. The energy of a signal x(t) is defined as
E=\int_{-\infty }^{\infty }\left| x(t)\right|^{2}dtA signal x(t) is called an energy signals if the energy is finite and power IS Zero.
The average power of a signal x(t) is defined as
P=\displaystyle \lim_{T \to \infty }\int_{-T/2 }^{T/2 }\left| x(t)\right|^{2}dtA signal x(t) is called a power signal if the average power P is finite and Energy is infinite.
Q.7. What is the period T of the signal x(t)=2\cos (\frac{t}{4})
Ans.
x(t)=2\cos (\frac{t}{4});
\Omega _{0}=\frac{1}{4};
T=\frac{2\Pi }{\Omega _{0}}=\frac{2\Pi }{1/4}=8\Pi secQ.8. Define continuous-time, discrete-time and digital signals.
Ans.
- Continuous-time signals: The signals that are defined at all instants of time are known as continuous-time signals.
- Discrete-time signals: The signals that are defined at discrete instants of time are known as discrete-time signals.
- Digital signals: The signals that are discrete in tune and quantized in amplitude are digital signals
Q.9. What is the value of the following integral?
\int_{-\infty }^{\infty }x(t)\delta (at-b)dtAns. \frac{1}{\left| a\right|}x\left ( \frac{b}{a} \right )
Q.10. What are the different types of representation of discrete-time signals?
Ans. Discrete-time Signal representation types are:
- Graphical representation
- Functional representation
- Tabular representation
- Sequence representation
Q.11. Consider the discrete-time signal x(n)=1-\sum_{k=3}^{\infty }\delta (n-1-k). Determine the value of the signals M and k so that x(n) may be expressed as x(n)=u(Mn-k)

The signal x(n) is sketched in above figure.
Ans.
The signal x(n) is equivalent to folding x(n) and then shifting the folded signal by 3 to the right. Therefore x(n) = u(-n+3). Comparing u(-n – 3) with u(Mn – nk) we get M = -1 and k = -3.
Q.12. Consider a continuous-time signal x(t)=\delta (t+2)-\delta (t-2). Calculate the value E_{\infty } of for the signal y(t)=\int_{-\infty }^{t}x(\tau )d\tau

y(t)=\int_{-\infty }^{t}x(\tau )d\tau =\int_{-\infty }^{t}[\delta (\tau +2)-\delta (\tau -2)]dt;
y(t)=u(t+2)-u(t-2);
E_{\infty }=\int_{-2}^{2}\left| y(t)\right|^{2}dt=[t]_{-2}^{2};
=4Q.13. Find the even and components of the signal x(t)=e^{jt}
Ans.
x_{e}(t)=\frac{x(t)+x(-t)}{2}=\frac{e^{jt}+e^{-jt}}{2}=\cos t;
x_{0}(t)=\frac{x(t)+x(-t)}{2}=\frac{e^{jt}-e^{-jt}}{2}=j\sin t