This set of Digital Communications Multiple Choice Questions & Answers (MCQs) focuses on “Classification of Signals”.

1. What is the period of a signal x(t) ?

a) T

b) 2T

c) T/2

d) None of the mentioned

View Answer

Explanation: A signal is said to be periodic if the duration of one complete cycle is T and it repeats itself after this duration.

2. Which of the given signals are periodic?

a) x(t) = 4 cos(5πt)

b) x(t) = u(t) – 1/2

c) x(t) = 4u(t) + 2sin(3t)

d) x[n] = 2sin(3n)

View Answer

Explanation: T=2π / 5π = 2/5 , periodic with period 2/5.

3. Check whether the signal is periodic or not?

x(t) = cos(4t) + 2sin(8t)

a) Periodic with period π/2

b) Periodic with period 2

c) Periodic with period 2/π

d) Not periodic

View Answer

Explanation: T1=2π /4 T2=2π /8, T1/T2 = 2 T=T1 or 2T2 , T=π /2

4. Find the periodicity of the following signal. x(t)=cos((2π/7)t)sin((3π/5)t)

a) 30

b) 7

c) 35

d) 5/3

View Answer

Explanation: T1=2π/2π/7 = 7 , T2=2π/3π/5=5/3 , T1/T2=5/21 , T=21T1 or 5T2 , T=35

5. Find the fundamental period of 1+sin^2 (3π/5)n .

a) 10/3

b) 5

c) 3π/5

d) None of the mentioned

View Answer

Explanation: sin^2(3π/5)n = (1-cos(6π/5)n)/2 = 1/2-1/2cos(6π/5)n ; period = 6π/(5*2π) = k/N = 3/5 ; N=5

6. Which signal is called as energy signal?

a) Finite energy and zero power

b) Finite energy and non-zero power

c) Infinite energy and zero power

d) Infinite energy and non-zero power

View Answer

Explanation: A signal is said to be energy signal if it has finite energy and zero average power.

7. Which signal is said to be power signal?

a) Infinite power and zero energy

b) Infinite power and non-zero energy

c) Finite power and infinite energy

d) Finite power and zero energy

View Answer

Explanation: A signal is said to be power signal if it has finite power and infinite energy.

8. Determine the periodicity and also find whether it is a power or energy signal?

e^(-at)u(t)

a) Periodic and energy signal

b) Non periodic and energy signal

c) Periodic and power signal

d) Periodic and energy signal

View Answer

Explanation: This is non periodic as it does not repeat itself after any period. And on calculating we will get energy as 1/2a which is finite.Thus it is an energy signal.

9. Continuous Impulse signal is a power or energy signal?

a) Power signal

b) Energy signal

c) Both power and energy

d) Neither power nor energy signal

View Answer

Explanation: On calculating using the power and energy calculation formula we will arrive at it is neither power nor energy signal.

10. Discrete impulse signal is a power or energy signal?

a) Power signal

b) Energy signal

c) Both power and energy signal

d) Neither power or energy signal

View Answer

Explanation: On calculating using energy formula we will get energy of this signal as 1 which is a finite value.Thus it is a energy signal.

11. An unit impulse function has ?

a) Large amplitude

b) Zero pulse width

c) Unity weight

d) All of the mentioned

View Answer

Explanation: An impulse function has infinite or large amplitude, zero pulse width and unity weight which is concentrated at zero.

**Sanfoundry Global Education & Learning Series – Digital Communications.**

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