# Viva Questions on Signals

## 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.

Viva Questions on Systems

### 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=1

and  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}dt

A 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}dt

A 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 sec

Q.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)dt

Ans. \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:

1. Graphical representation
2. Functional representation
3. Tabular representation
4. 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};

=4

Q.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