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Electronics and Communication Engineering - Signals and Systems

Exercise : Signals and Systems - Section 3
16.
Which one is a non-causal system?
y(n) = x(2n)
y(n) = x(n/2)
y(n) = x(n/2) + x(n)
all
Answer: Option
Explanation:

Because in (a) if you put n = 1 then y(n) = x(2) which shows output depend upon future value.

While in (b), (c) input converted to Past or Present and past.

Note that n cannot be in fraction so for x(n/2) you will put n = 2, 4, ... etc. not 1, 3, 5 .... etc.

17.
A linear system is characterized by H(ω) = Be-2ω2 the system is physically
unrealizable
realizable
depends upon B
depends upon constant 2
Answer: Option
Explanation:

Exponential function cannot be linear.

18.
The current in a circuit with 10 Ω resistance is i = 3 + 4 sin (100 t + 45°) + 4 sin (300 t + 60°) A. The rms current and power dissipated are
41 A and 410 W
35 A and 350 W
5 A and 250 W
11 A and 1210 W
Answer: Option
Explanation:

.

19.
Fourier transform pair are
autocorrelation and power spectral density
autocorrelation and convoloution
convolution and power spectral density
autocorrelation and energy
Answer: Option
Explanation:

This is property of autocorrelation.

F[R1, 1 (t)] = s(f) where s(f) is Power spectral density.

20.
The function x(t) is shown in the given figure. Even and odd parts of a unit step function ∪ (t) are respectively,
Answer: Option
Explanation:

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