# Electronics and Communication Engineering - Signals and Systems

### Exercise :: Signals and Systems - Section 2

1.

If f=0

 A. XL = 0 and XC = 0 B. XL = ∞, XC = ∞ C. XL = 0 and XC = ∞ D. XL = ∞ and XC = 0

Explanation: .

2.

An ac circuit has an impedance of (2 - j 9) Ω for third harmonic. The impedance for fundamental is

 A. 6 - j 27 Ω B. C. 2 - j 27 Ω D. 2 - j 3 Ω

Explanation: .

3.

The ROC of sequence x[n] = (0.8)n ∪[n] + (0.4)n ∪[n]

 A. |z| > 0.8 B. |z| > 0.4 C. 0.4 < |z| < 0.8 D. |z| < 0.8

Explanation: ROC ⇒ 1 - 0.8 z-1 < 0 1 - 0.4 z-1

⇒ 1 > 0.8 z-1z > 0.4

or z > 0.8

By combining both condition

ROC because z > 0.4

If you consider z > 0.8 then ROC between the limit 0 to 0.4 excluded.

4.

Pick the odd one

 A. variance B. standard deviation C. expectation D. chebyshev inequality

Explanation:

Because Variance, standard Deviation, Expectation are related to each other.

5.

The sampling of a function f(l) = sin 2pf0t starts from a zero crossing. The signal can be detected if sampling time T is

 A. B. C. D. Because fs ≤ 2f0, Ts .