Electronics and Communication Engineering - Exam Questions Papers

11.
The z-transform of a signal converges if and only if
Answer: Option
Explanation:

For u(n), a right handled sequence,

|z| > , |z| =

|3z| > 1; |2z| > 1

< 1; < 1.


12.
If the characteristic equation of a closed loop system is s2 + 2s + 2, then the system is :
over damped
critically damped
under damped
undamped
Answer: Option
Explanation:

1 + G(s) H(s) = 0

s2 + 2s + 2 = 0

ξ < 1, under damped.


13.
Given digits 2, 2, 3, 3, 3, 4, 4, 4, 4 how many distinct 4 digit numbers greater than 3000 can be formed?
50
51
52
54
Answer: Option
Explanation:

The given digits are 2, 2, 3, 3, 3, 4, 4, 4, 4 we have to find the numbers that are greater than 300

The first digit can be 3 or 4 but not 2.

Now, let us fix the first, second and third digits as 3, 2, 2, then the fourth place can be filled in 3 ways.

The number of ways is 3 similarly, we fix first third and fourth place as 3, 2 and 2 respectively (4) so the second place can be filled in 3 ways again,

The number of ways is 3

Now, we fix first, second and fourth, previous cases and we obtain the same result.

The number of ways is 3 so, the total number of ways is 9 similarly this can done by fixing the numbers as 3 and 4 (instead of 2) and thereby we obtain the a ways each

The number of numbers starting with 3 is 27

Similarly by taking 4 as the first digit we get 27 numbers

The number of numbers that are greater than 3000 is 27 + 27 = 54

But, 3222, 4222, is not possible as there are only two 2's, 3333 is not possible as there are only three 3's

The total number of numbers that are greater than 3000 is 54 - 3 = 51.


14.
Consider circuit with 4 : 16 Demux below: Now:
  1. f1 = (2, 6, 11, 12)
  2. f2 = (2, 5, 14)
  3. = p(2, 3, 4, 5, 9, 13, 14)

only 1 and 3 are correct
only 1 is correct
only 2 is correct
2 and 3 are correct
Answer: Option
Explanation:

f1 = y2 + y6 + y11 + y12

and f2 = y1 + yl0 + yl3

f1(m, n, o, p) = (3, 4, 9, 13)

f2(m, n, o, p) = (2, 5, 14)

= Π(2, 3, 4, 5, 9, 13, 14).


15.
The value of the integral is
Answer: Option
Explanation:

Compare this with

where s = 3.