# ECE - Questions and solutions set-8

Electronics and communication Engineering Questions and solutions set-8
Question:-
Option (A)
(et-e3t)u(t)
Option (B)
(e-t-3-3t)u(t)
Option (C)
(e-t+e-3t)u(t)
Option (D)
(et+e3t)u(t)
Correct Option:
B
Question Solution:
Y(s) = {2(s+2) / (s+1)(s+3)} x (1/ (s+2)) = { 2 / (s+1)(s+3)} , y(t) = (e-t -e-3t) u(t)
Question:-
Option (A)
1 / 16
Option (B)
1 / 8
Option (C)
1 /4
Option (D)
5 / 16
Correct Option:
D
Question Solution:
4 head & 0 tail 0r 3 head & 1 tail P = 4C0(1/2)4(1/2)0 + 4C3(1/2)3(1/2)1 = (5/16)
Question:-
Option (A)
n(x) = K exp(x/L)
Option (B)
n(x) = K exp(-x/ ÖL )
Option (C)
n(x) = K2 exp(-x/L)
Option (D)
n(x) = K exp(-x/L)
Correct Option:
D
Question Solution:
(d2x / dx2) – (n(x) / L2) = 0
{s2 - (1/L2) } n(x) = 0 , n(x) = Ae-x/2 + Bex/2
n(¥) = 0 \ B =0 , n(0) = k \ B =k
Question:-
Option (A)
(1 /10p) cos(3 x 108t + y)a^x A/m
Option (B)
(1/20p) cos(3 x 108t + y)a^x A/m
Option (C)
-(1/20p) cos(3 x 108t + y)a^x A/m
Option (D)
-(1/10p) cos(3 x 108t + y)a^x A/m
Correct Option:
A
Question Solution:

r = [40-120] p / [40+120] p = (-1/2)

\ r = -Ve `E will change direction & M will not change its direction

direction of `M for incident field is in x, so direction of `M in the reflected field is also is in x.

|Mc| = (|Ei r| / h) = {(24x(1/2)) / 120 p} = (1/10 p)
Question:-
Option (A)
Ö3
Option (B)
2 / Ö3
Option (C)
1
Option (D)
Ö3/2
Correct Option:
B
Question Solution:
|y(t)| = |M(w)||x (t)|
1 = (wp / Ö(w2 + p2))

w2 + p2 = w2 p2, 4 + p2 = 4p2
3p2 = 4, p = (2/Ö3)
Question:-
Option (A)
Gc(s) = (s+1)/(s+2)
Option (B)
Gc(s) = (s+2)/(s+1)
Option (C)
Gc = (s+1)(S+4) / (s+2)(s+3)
Option (D)
Gc(s) = 1+ (2/s) + 3s
Correct Option:
D
Question Solution:
E(s) = { sR(s) / (1+[G(s) + Gc(s)] H(s) }

So, Gc(s)|s ®0 should be maximum for error = ¥ Gc (s)|s ®0