Electronics and Communication Engineering - Signals and Systems

46. 

Which one is a causal system?

A. y(n) = 3x[n] - 2x[n - 1]
B. y(n) = 3x[n] + 2x[n + 1]
C. y(n) = 3x[n + 1] + 2x[n - 1]
D. y(n) = 3x[n + 1] 2x[n - 1] + x[n]

Answer: Option A

Explanation:

For causal output must depend upon Present and past not on future.


47. 

If , the coefficient of term e-t in f(t) will be

A. 1
B. 0
C. 0.5
D. 2/3

Answer: Option D

Explanation:

Coefficient of e-t = .


48. 

Double integration of a unit step function would lead to

A. an impulse
B. a parabola
C. a ramp
D. a doublet

Answer: Option B

Explanation:

.


49. 

If f(t) = A d(t - a), F(s) is

A. A e-as
B. A eas
C. A a e-as
D. Aa eas

Answer: Option A

Explanation:

It is an impulse having area A and originating at t = a.


50. 

If is the Laplace transform of f(t) then f(0+) is

A. 0
B.
C. 27
D.

Answer: Option C

Explanation:

.


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