# Electronics and Communication Engineering - Exam Questions Papers

6.

i1(t) for t > 0 is given by A. 2.5 - 2.5e-2t B. 2.5 - 1.25e-2t C. 1.25 - 1.25e-2t D. None of these

Explanation:

The time constant t is given by As Req = 4 || 4 = 2 Ω

i1(t) = iF - (iF - i1)e-t/t

ifinal = = 2.5 A

i1(t) = 2.5 - (2.5 - 1.25)e-t/1/2

i1(t) = 2.5 - 1.25e-2t.

7.

Find I in 4 Ω resistor.  A. 1 A B. 0.5 A C. 0.75 A D. 0.95 A

Explanation:

Apply KVL to first to first loop

6i1 - 2i2 = 10

(4 + R)i2 - 2i1 - 2i3 = 0

4i3 - 2i2 = 0

but i3 = 0.5 A

2 - 2i2 = 0

i2 = 1 A, 6i1 - 2 = 10

i1 = 2 A, (4 + R) - 2 X 2 -1 = 0

R = 1 Ω

Using Nodal analysis for loop 2

At node A, VA - 20 + VA + VA - VB = 0

3VA - VB - 20 = 0

3VA - VB = 20 ...(i)

At node B, 2VB - 2VA + 2VB + VB = 0

5VB - 2VA = 0 ...(ii)

Multiplying (i) by 2 and (ii) by 3

6VA - 2VB = 40

- 6VA - 15VB = 0

13VB = 40

VB ≅ 3 V 8.

Which of the following Boolean Expression correctly represents the relation between P, Q, R and M1? A. M1 = (P OR Q) XOR R B. M1 = (P AND Q) XOR R C. M1 = (P NOR Q) XOR R D. M1 = (P XOR Q) XOR R

Explanation:

M1 = Z XOR R

M1 = (X, Y) XOR R

= M1 = [P.Q.(P + Q)]XOR R

= (PQ + PQ) XOR R = (P XOR Q) XOR R.

9.

A sequential multiplexer is connected as shown in figure. Each time the multiplexer receives the clock, it switches to the next channel from 6 to 1. If the input signals are :
A = 10 cos 2p(4 x 103t)
B = 15 cos 2p(5 x 103t)
C = 20 cos 2p(6 x 103t)
D = 10 cos 2p(10 x 103t)
The minimum clock frequency should be __________ kHz. A. 8 kHz B. 50 kHz C. 20 kHz D. 10 kHz

Explanation:

Minimum clock freq. = 2fm

Where fm is highest freq. component = 2 x 10 kHz = 10 kHz.

10.

The Boolean function realized by the logic circuit shown is A. F = Σm(0, 1, 3, 5, 9, 10, 14) B. F = Σm(2, 3, 5, 7, 8, 12, 13) C. F = Σm(1, 2, 4, 5, 11, 14, 15) D. F = Σm(2, 3, 5, 7, 8, 9, 12)

Explanation: F = Σm (2, 3, 5, 7, 8, 9, 15).