Important Short Questions and Answers: Classification of Signals and Systems

1.    Define unit impulse and unit step signals.

Unit Impulse signal:

Amplitude of unit impulse is 1 as its width approaches zero. Then it has zero value at all other values.

Unit Step Signal:

The unit step signal has amplitude of 1 for positive values of independent variable and amplitude of 0 for negative of independent variable.

2. Give the mathematical and graphical representation of CT (continuous time) and DT (discrete time) impulse function.

CT and DT impulse function:

3. Define step and impulse function in discrete signals.

4. State the two properties of unit impulse function.

5. Find the fundamental period of signal

6.    Check e time whether the discrete signal sin 3n is periodic? The frequency of the discrete time signal is 3, because it is not a multiple of .

·              Therefore the signal is aperiodic.

7. Distinguish between deterministic and random signals.   or

       Define random signal and deterministic signal.

Random Signal:

       It has some degree of uncertainty before it actually occurs. The random signal cannot be defined by mathematical expressions.       

Deterministic Signal:

       There  is  no  uncertainty  occurrence.  It  is  completely  represented  by mathematical expressions.        

8. Determine the period of the signal

9.    When is a system said to be memory less? Give an example.

If the system output does not depend the previous input, it only depends the present input. Then the system is called memory less or static system.

 Eg:

y(t) = 2x(t) + x(t)

y(n) = x(n) + √x(n)

10. Define energy and power signals.

Energy Signal:                        

•  A signal is said to be an energy signal if its normalized energy is non zero and finite.               

•  For an energy signal, P = 0.

i.e., 0 < E < ∞

Power Signal: 

• A signal is said to be the power signal if it satisfies 0 < P < ∞

• For a power signal, E = ∞

11. What is the classification of system?

The classification of systems is,                          

(i). Linear and Non-Linear systems                     

(ii). Time invariant and Time varying systems.            

(iii). Causal and Non causal systems.

(iv). Stable and unstable systems.

(v). Static and dynamic systems.

(vi). Invertible and non invertible systems.

12. Verify whether the system described by the equation : y(t)=x(t)^z is linear and time invariant.

·              The system is linear since output is direct function of input.

·              The system is time variant since time parameter is squared in the given equation.

13. Draw the signal x(n) = u(n) – u(n-3)

14.      Check whether the following system is static/dynamic and casual/non casual y(n) = x(2n).

·              If n=1, y(1) = x(2). This means system requires memory. Hence it is dynamic system.

·              Since y(1) = x(2), the present output depends upon future input. Hence the system is non casual.

15.      Distinguish between static and dynamic system.

Static system:

• Does not require memory

• Impulse response is of the form h(t)=cω(t)

Dynamic system:

• Requires memory

• Impulse response can be any form except h(t)=cω(t)