# Electronics and Communication Engineering - Exam Questions Papers

31.

A two port network shown below is external dc sources. The voltages and the currents are measured with voltmeters V1 V2 and ammeter A1 A2 (all assumed to be ideal), as indicated. Under following switch conditions, the readings obtained are:
(i) S1 - Open, S2 - Closed A1 = 0A, V1 = 4.5 V, V2 = 1.5 V, A2 = 1 A
(ii) S1 - Closed, S2 - Open A1 = 4A, V1 = 6 V, V2 = 6 V, A2 = 0 A The h parameter matrix for this network is

 A. B. C. D. Answer: Option A

Explanation:

V1 = Z11I1 + Z12I2 → (1) Substitute (2) in (1) to get V1 in terms of I1 and V2

Thus H matrix = 32.

To realize following function 'f' How many minimum number of 2 input NAND gates are required?

 A. 3 B. 6 C. 4 D. 10

Answer: Option D

Explanation:

f1 = A B D + A B D + A B D + A B D = A D + A D = A ⊕ D

f = C D(A D + A D) + C D(A D + A D) Min. no. of 2 input NAND gate is 10.

33.

A uniform plane wave in air with H = 3 sin (ωt - 8x)uzA/m is incident normally on a region with σ = 0, μr = 1, εr = 9. The reflection coefficient is

 A. B. C. D. Answer: Option A

Explanation: .

34.

A memoryless source emits n symbols each with a probability p. The entropy of the source as a function of n

 A. increases as log n B. decreases as log (1/n) C. increases as n D. increases as n log n

Answer: Option C

Explanation:

H = n P log Since they all have same probability. Thus it increases with n.

35.

If (10) x x(10)x = (100)x; (100)x x (100)x = (10000)x then x can take value

 A. 2 B. 5 C. 10 D. All

Answer: Option D

Explanation:

(10)x x (10)x = (100)x

x x x = x2

(100)x x (100)x = (10000)x

x2 x x2 = x4

True for all values of x.

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