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Electronics and Communication Engineering - Exam Questions Papers

Exercise : Exam Questions Papers - Exam Paper 7
26.
The skin-depth of copper at a frequency of 3 GHz is 1 micron. At 12 GHz, for a non-magnetic conductor whose conductivity is times of copper, the skin depth would be :
9 x 4 μm
Answer: Option
Explanation:

.

27.
If the z-transform of x(n) is given by then the filter it represents is __________ .
low pass
high pass
band pass
all pass
Answer: Option
Explanation:

i.e. we can see that

According to the property, the filter is an all-pass filter.

28.
The system of linear equations 4x + 2y = 1 , 2x + y = 6 has
a unique solution
no solution
an infinite number of solutions
exactly two distinct solutions
Answer: Option
Explanation:

4x + 1y = 7 → (1)

2x + y = 6 → (2)

(1) can be written as 2x + y = 3.5 → (3)

Now LHS of equations (2) and (3) are same but RHS is different which is not possible. Hence no solution.

29.
Which of the following periodic waveforms will have only odd harmonics of sinusoidal waveform?




Select the correct option using the codes given below Codes:
1 and 2
1 and 3
1 and 4
2 and 4
Answer: Option
Explanation:

The conditions for a signal s(t) to have odd harmonics of sinusoidal waveforms alone are given by

(i) , where T is the period and

(ii) s(t) = - s(t) [i.e., odd function]

The waveforms (1) and (2) satisfy condition (b).

30.
A control system is as shown in given figure The maximum value of gain K for which the system is stable is
more than 5
equal to 5
less than 1
less than 5
Answer: Option
Explanation:

Characteristic Equation is 1 + GH = 0

1 +

or s3 + 3s2 + 2s + (1 + K) = 0

Hurwitz criterion can be applied

s3 1 2 and (1 + K) both should be + ve

s2 3 1 + K

s1 0 ∴ K should be more than - 1 and less than 5

s0 1 + K.

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