# Electronics and Communication Engineering - Exam Questions Papers

1.

If X = 1 in the logic equation [X + Z { Y + (Z + X Y)}] { X + Z (X + Y)} = 1, then

 A. Y = Z B. Y = Z C. Z = 1 D. Z = 0

Explanation:

[1 + z{y + z + y}][0 + z] = 1, z = 1, z = 0.

2.

(22)4 + (101)3 - (20)5 = (x)4 + (4)x+1 where x > 4. The value of x is

 A. 6 B. 4 C. 12 D. 8

Explanation:

(22)4 + (10)10 - (10)10 = (22)4

Since x > 4, i.e. all the number systems with base greater than 4.

All these will contain symbol '4' which will have same value in all bases.

Converting 4 into base '4'

system (4)10 (10)4

Now (22)4 = (x)4 + (10)4

(x)4 = (22)4 - (10)4 = (12)4

x = 12.

3.

Consider a system with the transfer function . Its damping ratio will be 0.5 when the value of k is :

 A. 2/6 B. 3 C. 1/6 D. 6

Explanation:

ξ = 0.5,  We take second term only  .

4.

For the system with given characteristic equation
s5 + 4s4 + 8s3 + 8s2 + 7s + 4 = 0
The number of roots on left hand side, right hand side and imaginary axis are respectively.

 A. 3, 2, 0 B. 4, 0, 1 C. 3, 0, 2 D. 4, 1, 0

Explanation:

Apply Routh Hurwitz criteria.

5.

A series RLC circuit has a resonance frequency of 1 kHz and a quality factor Q = 100. If each of R, L and C is doubled from its original value, the new Q of the circuit is

 A. 25 B. 50 C. 100 D. 200

Explanation:

Resonant frequency Quality factor = where R, L, C all are doubled, then    .