This set of Signals & Systems Questions and Answers for Freshers focuses on “Signal Classification and Properties – 2”.

1. A signal is a physical quantity which does not vary with ____________

a) Time

b) Space

c) Independent Variables

d) Dependent Variables

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Explanation: A signal is a physical quantity which varies with time, space or any other independent variables. Therefore, it does not vary with dependent variables.

2. Most of the signals found in nature are _________

a) Continuous-time and discrete-time

b) Continuous-time and digital

c) Digital and Analog

d) Analog and Continuous-time

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Explanation: Signals naturally are continuous-time signals. These are also known as analog signals. Continuous-time or analog signals are defined for all values of time t.

3. Which one of the following is not a characteristic of a deterministic signal?

a) Exhibits no uncertainty

b) Instantaneous value can be accurately predicted

c) Exhibits uncertainty

d) Can be represented by a mathematical equation

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Explanation: Deterministic signal is one which exhibits no uncertainty and its instantaneous value can be accurately predicted from its mathematical equation. Therefore, a deterministic signal doesn’t exhibit uncertainty. However, a random is always uncertain.

4. Determine the fundamental period of the following signal:sin60t.

a) 1/60 sec

b) 1/30 sec

c) 1/20 sec

d) 1/10 sec

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Explanation: Consider the equation: sinΩ

_{0}t. Comparing this equation with the one given in the question: sin60t

⇒ Ω

_{0}=60π

5. Sum of two periodic signals is a periodic signal when the ratio of their time periods is ____________

a) A rational number

b) An irrational number

c) A complex number

d) An integer

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Explanation: Sum of two periodic signals is a periodic signal only when the ratio of their time periods is a rational number or it is the ratio of two integers. For e.g., T1/T2 = 5/7 → Periodic; T1/T2 = 5 → Aperiodic.

6. Determine the Time period of: x(t)=3 cos(20t+5)+sin(8t-3).

a) 1/10 sec

b) 1/20 sec

c) 2/5 sec

d 2/4 sec

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7. What is the even component of a discrete-time signal?

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8. Determine the odd component of the signal: x(t)=cost+sint.

a) sint

b) 2sint

c) cost

d) 2cost

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9. Is the signal sin(t) anti-symmetric?

a) YES

b) NO

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Explanation: A signal is said to be anti-symmetric or odd signal when it satisfies the following condition:

⇒ x(t) = – x(t)

Now, here, x(t) = sin(t) ⇒ x(-t) = sin(-t) = – sin(t)

∴ Sin(t) is an anti-symmetric signal or an odd signal.

10. For an energy signal __________

a) E=0

b) P= ∞

c) E= ∞

d) P=0

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Explanation: A signal is called an energy signal if the energy satisfies 0<E< ∞ and power P=0.

11. Determine the power of the signal: x(t) = cos(t).

a) 1/2

b) 1

c) 3/2

d) 2

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12. Is the following signal an energy signal?

x(t) = u(t) – u(t – 1)

a) YES

b) NO

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13. A signal is anti-causal if ______________

a) x(t) = 0 for t = 0

b) x(t) = 1 for t < 0

c) x(t) = 1 for t > 0

d) x(t) = 0 for t > 0

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Explanation: A signal is said to be anti-causal when x(t) = 0 for t > 0.

14. Is the signal x(t)= e^{at} u(t) causal?

a) YES

b) NO

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Explanation: A signal is said to be causal if it is 0 for t < 0.

Now, we know, u(t) = 1 for t ≥ 0.

∴ x(t)= e

^{at}for t ≥0 .

∴ The signal is 0 for t < 0.

∴ The signal is causal.

15. Is the signal x(n) = u(n + 4) – u(n – 4) causal?

a) YES

b) NO

View Answer

Explanation: A signal is said to be causal if it is 0 for t < 0.

⇒ u (n + 4) = 1 for n ≥ – 4

⇒ u(n – 4) = 1 for n ≥ 4

∴ The signal x (t) is defined for the interval [-4, 4] and it is zero for all other n values.

∵ The signal is defined for both n > 0 and n < 0

∴ The signal is non-causal.

**Sanfoundry Global Education & Learning Series – Signals & Systems.**

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