Quiz: Electrical Engineering 07 Sep 2020

Quiz: Electrical Engineering
Exam: UPPSC-AE
Topic: Miscellaneous

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

Q1. The stator of a 3 phase, 10 pole induction motor possesses 120 slots. If a lap winding is used, calculate the coil pitch, if the coil width extends from slot 1 to slot 11.
(a) 72.12 %
(b) 83.30 %
(c) 12 %
(d) 42 %

Q2. In a three-phase induction motor, the ratio of starting current to full load current is 12.56 and the ratio of starting torque to full load torque is 1.6. percentage slip at full load is………
(a) 01. %
(b) 1%
(c) 12.56 %
(d) None of the above

Q3. The output signal of a common-collector amplifier always:
(a) Larger than the input signal
(b) In phase with the input signal
(c) Out of phase with the input signal
(d) Exactly equal to the input signal

Q4. An amplifier has a gain of 20 without feedback. If 10% of the output voltage is fed back by means of resistance negative feedback circuit, the overall gain would be
(a) 19.80
(b) 16.55
(c) 10.85
(d) 6.67

Q5. Phase reversed of 180⁰ as compared to input occurs in the output of
(a) CE amplifier
(b) CB amplifier
(c) CC amplifier
(d) All of the above

Q6. A single phase, half-wave, controlled rectifier has 400 sin⁡〖(314 t)〗 as the input voltage and R as the load. For a firing angle of 60⁰ for the SCR, the average output voltage is
(a) 200/π
(b) 240/ π
(c) 300/ π
(d) 400/ π

Q7. A Potentiometer is basically a
(a) Deflection type instrument
(b) Null type instrument
(c) A digital instrument
(d) Both a and b

Q8. When measuring insulation resistance of a cable using DC source, the galvanometer used should be initially short circuited because
(a) Cable have a low value of initial resistance
(b) Cable have a low value of capacitance which draws a high value of charging current
(c) Cable have a high value of capacitance which draws a high value of charging current
(d) None of the above

Q9. What is the value of charging current in short transmission lines?
(a) Less than medium transmission lines
(b) Equal to medium transmission lines
(c) More than medium transmission lines
(d) More than long transmission lines

Q10. Voltage regulation of a transmission line should be ________
(a) Minimum
(b) Maximum
(c) Greater than 50 %
(d) Less than 50 %

SOLUTIONS
S1. Ans.(b)
Sol. pole pitch=120/10=12
Coil pitch=11-1=10
If coil pitch= pole pitch, then it is full pitch winding, if not then it is short pitch winding.
Here coil-pitch covers slot1 to slot 11 i.e. 10 slots.
∴% of Coil-pitch = 10/12×100=83.3 %

S2. Ans.(b)
Sol. In a three-phase induction motor, Tst/Tfl =(Ist/Ifl )^2 Sfl
∴1.6=(12.56)^2 Sfl
∴s_fl=0.01 or 1%

S3. Ans.(b)
Sol. The output signal of a common-collector amplifier always in phase with input signal.

Parameter Common Base Common Emitter Common Collector
Voltage Gain High, Same as CE High Less than Unity
Current Gain Less than Unity High High
Power Gain Moderate High Moderate
Phase inversion No Yes No

S4. Ans.(d)
Sol. Given that, A=20 and β=10%=0.1
∵feedback is Negative.
∴Av=A/(1+Aβ)=20/(1+20×0.1 )=20/3=6.67

S5. Ans.(a)
Sol. Phase reversed of 180⁰ as compared to input occurs in the output of CE amplifier.

S6. Ans.(c)
Sol. A single phase, half-wave, controlled rectifier, V_avg=Vm/2π(1+cos⁡〖α)〗
∵Vavg=400/2π(1+cos⁡〖60⁰)=(400×3)/(2π ×2)〗=300/π

S7. Ans.(b)
Sol. A potentiometer is a null type instrument because the reading of the unknown voltage is measured when the current flowing through the galvanometer is zero (Ig=0).

S8. Ans.(c)
Sol. When measuring insulation resistance of a cable using DC source, the galvanometer used should be initially short circuited because Cable have a high value of capacitance which draws a high value of charging current. i.e. I_C=V(ωC), As C is high 〖,I〗_C is high.

S9. Ans.(a)
Sol. Line to Earth capacitance of short transmission line is less than that in medium and long transmission line and is negligible. Because of this the charging current of short transmission line is less than that in medium and long transmission line and is negligible.

S10. Ans.(a)
Sol. More value of voltage regulation means more voltage fluctuations and this is undesirable. So, the value of voltage regulation should be as low as possible.

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