Electronics and Communication Engineering - Exam Questions Papers

Exercise :: Exam Questions Papers - Exam Paper 1

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

A.	i(t) = 0.5 - 0.125e^-1000t A
B.	i(t) = 1.5 - 0.125e^-1000t A
C.	i(t) = 0.5 - 0.5e^-1000t A
D.	i(t) = 0.375e^-1000t A

Answer: Option A

Explanation:

i(f) = 0.5, i(i) = 0.75

i(t) = V_r + (i_i - i_j)e^-1/p = 0.5 - 0.125e^-1000t .

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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

A.	7.6237 x 10^-4 A/cm²
B.	7.6237 x 10^-5 A/cm²
C.	7.6237 x 10^-3 A/cm²
D.	none of these

Answer: Option A

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, ∴ n_i = 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.

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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?

A.	The system is completely state controllable for any non zero values p and q
B.	Only p = 0 and q = 0 result in controllability
C.	The system is uncontrollable for all values of p and q
D.	We cannot conclude about controllability from the given data

Answer: Option C

Explanation:

Use the condition of controllability.

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A MOSFET has a threshold voltage of 1 V and oxide thickness of 500 x 10^-8 [ε_r = 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 __________ .