Electronics and Communication Engineering - Signals and Systems

21. 

If then for this to be true x(t) is

A. exp (j2p f/t)
B. exp (-j2p f/t)
C. exp (j2p ft)
D. exp (-j2p f/t)

Answer: Option C

Explanation:

If

.


22. 

For the discrete time system of the given figure

A. yk - 0.5 yk - 1 - 0.25 yk - 2 = uk
B. yk + 0.5 yk - 1 - 0.25 yk - 2 = uk
C. yk - 0.5 yk - 1 + 0.25 yk - 2 = uk
D. yk + 0.5 yk - 1 + 0.25 yk - 2 = uk

Answer: Option C

Explanation:

uk + 0.5 yk - 1 - 0.25 yk - 2 = yk.


23. 

The analog signal m(t) is given below m(t) = 4 cos 100 pt + 8 sin 200 pt + cos 300 pt, the Nyquist sampling rate will be

A. 1/100
B. 1/200
C. 1/300
D. 1/600

Answer: Option C

Explanation:

m (t) = 4 cos 100 pt + 8 sin 200 pt + cos 300 pt

Nyquist sampling freq fs ≤ 2fm where fm is highest frequency component in given signal and highest fm in 3rd part

2pfmt = 300 pt

fm = 150 Hz

fs = 2 x 150 p 300 Hz

.


24. 

The ROC of sequence in the Z.T. of sequence x[n] = an ∪ [n] is

A. z > a
B. z < a
C. |z| > a
D. |z| < a

Answer: Option C

Explanation:

The simplest method to find the ROC. Put denominator to greater than zero.


25. 

In Laplace transform, multiplication by e-at in time domain becomes

A. translation by a in s domain
B. translation by (-a) in s domain
C. multiplication by e-as in s domain
D. none of the above

Answer: Option A

Explanation:

£e-at f(t) = F(s + a).