Quiz: Electrical Engineering 2 June 2021

Quiz: Electrical Engineering
Exam: DFCCIL
Topic: Signals and systems

Each question carries 1 mark.
Negative marking: 1/4 mark
Time: 10 Minute

Q1. For even function, the necessary condition is
(a) f(t) = -f(-t)
(b) f(t) = +f(-t)
(c) f(t) = 1/(f(-t))
(d) f(t) = -f (t ± T/2)

Q2. Energy of the signal A 𝛿[n] is
(a) A^2
(b) A^2/2
(c) A^2/4
(d) 0

Q3. Which one of the following is correct?
Power of an Energy signal is
(a) finite
(b) zero
(c) infinite
(d) between 0 and ∞

Q4. Laplace Transform of sin2t is
(a) 4/(s^2 + 2)
(b) 4/(s^2 + 4)
(c) 2/(s^2 + 4)
(d) 2/(s^2 + 2)

Q5. For Half-wave(odd) symmetry, with T_o = period of x(t), which one of the following is correct?

(a) x(t ± To/2) = -x(t)
(b) x(t ± To/2) = x(t)
(c) x(t ± To) = -x(t)
(d) x(t ± To) = x(t)

Q6. The signal x(n) shown in the below figure is a

(a) periodic discrete time signal
(b) periodic signal
(c) non-periodic signal
(d) periodic discrete time signal consisting of 3 non-zero samples

Q7. Which one of the following must be satisfied if a signal is to be periodic for -∞ < t < ∞?
(a) x(t + To) = x(t)
(b) x(t + To) = dx(t)/dt
(c) x(t + To) = ∫_t^(To)▒〖x(t)〗dt
(d) x(t + To) = x(t) + kTo

Q8. What is the period of the sinusoidal signal x(n) = 5cos[0.2πn]?
(a) 10
(b) 5
(c) 1
(d) 0

Q9. A Discrete signal is said to be even or symmetric if X(-n) is equal to __
(a) 0
(b) X(n)
(c) –X(n)
(d) –X(-n)

Q10. Determine the fundamental period of the signal

x(t)=cos⁡(2t+π/4)
(a) π sec.
(b) 2π sec.
(c) π/4 sec.
(d) π/2 sec.

SOLUTIONS

S3. Ans.(b)
Sol.
A power signal has infinite energy and an energy signal has zero average power.
Transient (finite duration) signals are energy signals while periodic signals are power signals.

S4. Ans.(c)
Sol. We know that Laplace Transform of sinωt is ω/(s^2 + ω^2 )
So, Laplace Transform of sin2t is 2/(s^2 + 4)

S5. Ans.(a)
Sol. For Odd half-wave symmetry –
x(t) = -x(t±To/2)

S6. Ans.(c)
Sol. It is a Discrete Time non-periodic signal.

S7. Ans.(a)
Sol. A signal is a periodic signal if it completes a pattern within a measurable time frame, called a period and repeats that pattern over identical subsequent periods.
i.e., x(t)=x(t + To)
where; T_o= fundamental period of the signal

S8. Ans.(a)
Sol. Given:
x(n) = 5cos[0.2πn]
We know that, Time period of a discrete time signal is –
⇒ N = 2π/ω
Here,
ω = 0.2π
So, N = 2π/0.2π = 10

S9. Ans.(b)
Sol. Any signal is said to be even or symmetric if f(x) = f(-x) is True otherwise system may be asymmetric.
Hence, A Discrete signal is said to be even or symmetric if X(-n) = X(n)

S10. Ans.(a)
Sol. Given; x(t)=cos⁡(2t+π/4)
Here, ω=2
Fundamental period(T_0 )=2π/ω=2π/2=π sec.

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