Civil Services Preliminary Examination ELECTRICAL ENGINEERING previous Paper

Civil Services Preliminary Examination ELECTRICAL ENGINEERING previous Paper
 

1.. The characteristic impedance of an air dielectric co-axial line is 77Ω If the air is replaced by a dielectric with E _r = 2.28, the characteristic impedance will be

(a) 33.8Ω

(b) 51Ω

(c) 116Ω

(d) 175Ω

Ans:-B

2. The core diameter of a step index optical fibre ranges from

(a) 300 μ m to 500 μ m

(b) 300 mm to 500 mm

(c) 30nm to 40 nm

(d) 2 μ m to 200 μ m

Ans:-B

3. An infinitely long dielectric cylinder of relative permitivity, ε _r is placed in air in a uniform electric field of magnitude E directed perpendicular to its axis. The stress within the cylinder is

(a) 2 / (1+ ε _r ) E

(b) 2 / ( l + 2ε _r ) E

(c) 3 / 2+ ε _r E

(d) 2ε _r / 1+ ε _r E

Ans:-A

4.. If the E field in a plane electromagnetic wave travelling along the z-axis is given by

E = (a _x + a y) f (ω t—β z ) + (a_x + a_y) f (ω t + β z )

The H field associated with the wave is (z ₀ is the characteristic impedance)

(a) (a x + ay) f (ω t – β z) /z ₀ (a_x + a_y) f (ω t + β z )/z₀

(b) (a x— ay) f (ω t — β z) /z ₀ + (ax—ay) f (ω t + β z) / Zo

(c) (ay — a x) f (ω t — β z) /z _o + (-a_y + a_x) f (ω t + 3z)/z

(d) (a _x—a y) f (ω t — β z) / z ₀ +  (ay – ax ) f (ω t + β z )/z

Ans:-D

5. The Laplace transform of current In an RLC series circuit with

R = 2 Ω, L = 1H and C = 1/2 F is

I(s) = 1/ s² +2s+2

The voltage across the Inductor ‘L’ will be

(a) e^-t sin tu (t)

(b) e^-t cos t u (t)

(c) e^-t (sin t + cos t) u (t)

(d) e^-t (cos t — sin t) u (t)

Ans:- B

6. The Fourier transform of unit Impulse function (t) would be

(a) 1 / (2 + ω²)

(b) (2 + ω²)

(c) 1

(d) ½

Ans:-C

7. The response of a system by d²i / dt² + i = v. If the excitation is v = ke^2t, then the forced response of i for t > 0 will be

(a) K / 3 e^t

(b) K / 5 ^{e -t}

(c) K / 5 e ^2t

(d) K / 3 sin t + k / 5 cost

Ans:-C

8. Consider the following data in respect of a certain digital gate:

I _OH = 0.2 mA, I _OL = 16 mA, I _IH = 40 μA and I _IL = 1.6 mA

The symbols have their usual meanings. The ‘fanout’ will be

(a) 80

(b) 40

(c) 10

(d) 5

Ans:-B

9. Which one of the following statements regarding the state transition matrix is correct?

(a) φ (0) = 0

(b) φ (0) = φ (1/t)

(c) φ (t1 + t₂) = φ (t₁) + φ (t₂)

(d) φ (t1 — t2) φ (t₁ — t₀) = φ (t ₂— t₀)

Ans:-D

10. The average value of dc voltage of a single-phase semi converter under continuous conduction is

(a) √2V (1+ cos α) / π

(b) √2V (1— cos α) / π

(c) √2V (1+cosα) / π

(d) √2V (l—cos α) / π

Ans:-A