# Electronics and Communication Engineering - Exam Questions Papers

11.

The reduced form of the function
X(E, A, B, C, D) = ∑(0, 1, 2, 3, 4, 7, 8, 9, 10, 12, 15, 16, 17, 18, 19, 20, 23, 24, 25, 26, 28, 31) is

 A. B. C. D. Explanation: X =(A + B + D)(A + B + D) (A + B + C + D)

=(D + A D + B D + AB + A D + A B + B D) (A + B + C + D)

=(D + AB + A B)(A + B + C + D) .

12.

Consider the probability density f(x) = ae-b|x| where x is a random variable whose allowable values range from x = - ∞ to x = + ∞. The Cdf (Cumulative distribution function) for x ≥ 0 is :

 A. B. C. D. Explanation: .

13.

The electric field of uniform plane wave is given by E = 20 sin (2 p x 108t- pz) x + 20 cos (2 p x 108t - pz) y. The corresponding magnetic field is

 A. B. C. D. Explanation: H = Hx + Hy .

14.

Find I for circuit shown below A. 3 A B. 1 A C. 2 A D. 0 A

Explanation:

Mesh Analysis Apply KVL at loop 2

125i2 - 100i3 = 0 ...(i)

Apply KVL at loop 3

120i3 - 100i2 - 20i1 = 0

i1 = 5A

120i3 - 100i2 - 100 = 0

120i3 - 100i2 = 100 ...(ii)

From (i) 125i2 - 100i3 = 0 ...(iii)

Put equation (iii) in eq. (ii)

120i 3 - 100i2 = 100

120 x - 100i2 = 100

150i2 - 100i2 = 100

50i2 = 100

i2 = 2A.

15.

A n-type silicon sample contains a donor concentration of Nd = 2 x 1016 cm-3. The minority carrier hole lifetime is tp0 = 5 μs. The thermal equilibrium generation rate of hole is:

 A. 1.125 x 109 cm-3 s-1 B. 0.625 x 109 cm-3 s-1 C. 4.5 x 109 cm-3 s-1 D. 2.25 x 109 cm-3 s-1

Explanation: Then thermal generation rate = 2.25 x 109 cm3 S-1 .