Electronics and Communication Engineering - Exam Questions Papers
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6.
In the circuit shown, in switch S is open for a long time and is closed at t = 0. The current i(t) for t ≥ 0+ is


Answer: Option
Explanation:
i(f) = 0.5, i(i) = 0.75
i(t) = Vr + (ii - ij)e-1/p = 0.5 - 0.125e-1000t .
7.
In a semiconductor material. The hole concentration is found to be 2 x 2.5 x 1015 cm-3. If mobility of carriers is 0.13 m2/ v-s. Then find the current density if electric field intensity is 3.62 x 10-19
Answer: Option
Explanation:
Current density J = σE
Where σ = conductivity
Given -> μ = 0.13 m2/v-s = 0.13 x 104 cm2/V sec
P = 2.25 x 1015/cm3
We have, ∴ ni = 1.5 x 1010
Also n.p. =
∴ n = /p
= (1.6 x 10-19 x 0.13 x 104 x 2.25 x 1015) x
= (0.468) (4.5 x 1015)
σ = 2.106 x 1015 μ/cm
J = σE
∴ Current density = 2.106 x 1015 x 3.620 x 10-19
= 7.6237 x 10-4 A/m2.
8.
Consider the system
with
and
where p and q are arbitrary real numbers. Which of the following statements about the controllability of the system is true?



Answer: Option
Explanation:
Use the condition of controllability.
9.
A MOSFET has a threshold voltage of 1 V and oxide thickness of 500 x 10-8 [εr = 3.9; ε0 = 8.85 x 10-14 F/cm, q = 1.6 x 10-19 c]. The region under the gate is ion implanted for threshold voltage tailoring. The base and type of impant required to shift threshold voltage to - 1 V are __________ .
Answer: Option
Explanation:
VT(new) = VT(odd) +
= 6.903 x 10-8
∴
∴
fB = - 8.6 x 1011
The threshold voltage is always negative for p-channel and hence implant is of p-type.
10.
What is the propagation constant for air filled wave guide with dimensions a = 1.59" and b = 0.795" at 4.95 GHz?
Answer: Option
Explanation:
Here,
a = 1.59'' = 40.386 mm = 4.04 cm
∴ .
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