Quiz: Electrical Engineering 28 Jan 2021

Quiz: Electrical Engineering
Exam: NPCIL
Topic: Miscellaneous

Each question carries 1 mark.
Negative marking: 1/4 mark
Time: 10 Minute

Q1. Fermion particles obey
(a) Maxwell-Boltzmann statistics
(b) Heisenberg uncertainty principle
(c) Pauli’s exclusion principle
(d) Bose-Einstein statistics

Q2. An ac source of 200 V rms supplies an active power of 1200 W and a reactive power of 1600 VAR to a load. The rms current and the power factor of load respectively are
(a) 20 A and 0.6
(b) 8 A and 0.8
(c) 10 A and 0.8
(d) 10 A and 0.6

Q3. Torque/weight ratio of an instrument indicates
(a) Selectivity
(b) accuracy
(c) Fidelity
(d) Sensitivity

Q4. Decibel scale is useful while measuring voltages covering
(a) wide frequency ratio
(b) wide voltage ratio
(c) narrow frequency range
(d) narrow voltage range

Q5. An ideal voltage source will charge an ideal capacitor
(a) in infinite time
(b) exponentially
(c) instantaneously
(d) none of these

Q6. Which of the following materials is used to absorb moisture from air entering the transformer?
(a) Silica sand
(b) Silica gel
(c) Felt pad
(d) Sodium chloride

Q7. Which of the following acts as a protection against high voltage surges due to lightening and switching?
(a) Horn gaps
(b) Thermal overload relays
(c) Conservator
(d) Breather

Q8. The Transfer function (V_2 (s))/(V_1 (s))=10s/(S^2+10s+100) is for an active
(a) low pass filter
(b) high pass filter
(c) band pass filter
(d) all pass filter

Q9. In a two-winding transformer, the primary and the secondary induced emfs E1 and E2 are always
(a) In phase with each other
(b) Antiphase with each other
(c) Of different frequency
(d) Equal in magnitude

Q10. A d.c. motor runs at 1810 r.p.m. at full-load and 1865 r.p.m. at no-load. The speed regulation is ………
(a) 1.06%
(b) 3.03%
(c) 6.05%
(d) 5.08%

Solution

S1. Ans. (c)
Sol. Pauli’s exclusion principle

S2. Ans. (d)
Sol. V=200 V rms,P=1200 W,Q=1600 VAR
S=√(1200^2+1600^2 )=2000 VA and Cos ∅=P/s=1200/2000=0.6
I=S/V=2000/200=10 A

S3. Ans. (d)
Sol. Torque/weight ratio of an instrument indicates sensitivity.

S4. Ans. (a)
Sol. Decibel scale is useful while measuring voltages covering wide frequency ratio.

S5. Ans. (c)
Sol. instantaneously; Ideal voltage has zero internal resistance.
So, time constant τ=RC=0, Hance capacitor will charge instantaneously.

S6. Ans. (b)
Sol. Silica Gel

S7. Ans. (a)
Sol. Horn Gap

S8. Ans. (c)
Sol. For the Transfer function (V_2 (s))/(V_1 (s))=10s/(S^2+10s+100) when
s→0 (V_2 (s))/(V_1 (s))=0 and s→∞ (V_2 (s))/(V_1 (s))=0 But in between 0<s<∞ (V_2 (s))/(V_1 (s))≠0

S9. Ans. (a)
Sol. In phase with each other.

S10. Ans.(b)
Sol. Speed regulation = (N_0 -N_FL)/N_FL ×100=(1865-1810)/1810×100 = 3.03%

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