Electronics and Communication Engineering - Exam Questions Papers

36. 

In the following transistor circuit VBE = 0. 7 V, rc = 25mV/IE, and β and the capacitance are very large

The value of DC current IE is

A. 1 mA
B. 2 mA
C. 5 mA
D. 10 mA

Answer: Option A

Explanation:

Design is independent of IB as β is very high

IB ∼ 0

Thus applying Kirchhoff's law is base emitter, we get.


37. 

A certain JK FF has tpd = 12 nsec. The largest MOD counter that can be constructed from these FFs and still operate up to 10 MHz is

A. any
B. 8
C. 256
D. 10

Answer: Option B

Explanation:

f0 = 107 Hz

⇒ 8.33

n = 8.


38. 

A second-order system has a transfer function is given by . If the system, initially at rest is subjected to a unit step input at t = 0, the second peak in response will occur at :

A. p sec
B. p/3 sec
C. p/6 sec
D. p/2 sec

Answer: Option C

Explanation:

Peak time

.


39. 

Value of ZL for maximum power transfer is

A. R
B. R + jωL
C. R - jωL
D. None of these

Answer: Option C

Explanation:

The value of load for maximum power transfer is given by complex conjugate of ZAB. ZAB = R + jXL = R + jωL.

ZL for maximum power transfer is given by, ZL = R - jωL.


40. 

A periodic voltage has following values for equal time intervals changing suddenly from one value to next : 0, 5, 10, 20, 50, 60, 50, 20, 10, 5, 0, - 5, - 10 etc.
RMS value of the waveform is :

A. 31 v
B. 32 v
C. insufficient data
D. none of these

Answer: Option A

Explanation:

Mean value of V2 =

= 965 V

rms value = ≈ 31 V.