# Electronics and Communication Engineering - Exam Questions Papers

1.

The electric field of 2.5 x 107 V/m can give 1 eV energy to condition electron, then in a copper block what will be the mean free path of electron?

 A. 5 x 10-8 m B. 4 x 10-7 m C. 0.4 m D. 0.5 m

Explanation:

The force on electron in eE. As the electron moves through distance d , the work done on it is eEd.

This is equal to energy transferred to electron.

eEd = 1 eV

d = 4 x 10-7m.

2.

25 persons are in a room. 15 of them play hockey, 17 of them play football and 10 of them play both hockey and football. Then the number of persons playing neither hockey nor football is:

 A. 2 B. 17 C. 13 D. 3

Explanation:

Representing the given information in the Venn diagrams, we have Let the number of people who play only hockey = a

The number of people who play only football = b

Now, a = n(H) - 10 = 15 - 10 = 5

b = n(F) - 10 = 17 - 10 = 7

Clearly, a + b + 10 + n = 25

n = 25 - 7 - 5 -10 ⇒ n = 3

The number of people who do not play neither Hockey nor Football is 3.

3.

For the circuit shown in the following figure I0-I3 are inputs to the 4:1 multiplexer R(MSB) and S are control bits The output Z can be represented by

 A. PQ + PQ S + Q R S B. P Q + PQ R + P Q S C. P Q R + P QR + PQRS + Q R S D. PQ R + PQR S + P Q R S + Q R S

Explanation:

Use this to find solution 4.

The transfer function of a system is . For a unit-step input to the system the approximate setting time for 2% criterion is :

 A. 100 sec B. 4 sec C. 1 sec D. 0.01 sec

Explanation:    ξωn = 1 for 2% = 4 sec.

5.

The Nyquist sampling interval, for the signal sine (700t) + sine (500t) is

 A. B. C. D. Explanation:

g(t) = sinc (700t) + sinc (500t) g(t) is band-limited with fM = 350 Hz.

Hence the Nyquist rate will be 700 Hz.

Then Nyquist interval is sec.