Quiz: Electrical Engineering 12 June 2021

Quiz: Electrical Engineering
Exam: AE/JE
Topic: Miscellaneous

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

Q1. An overhead transmission line is provided with earth wire for protection against
(a) Lightning surge
(b) Switching surge
(c) Power frequency overvoltage
(d) None of the above

Q2. A lightning arrester provides
(a) Low resistance path
(b) Low impedance path
(c) High impedance path
(d) None of the above

Q3. A device having characteristics very close to that of an ideal voltage source is
(a) Vacuum diode
(b) Transistor
(c) FET
(d) Zener diode

Q4. A tunnel diode is
(a) A slow switching device
(b) An amplifying device
(c) A very heavily doped p-n junction diode
(d) High resistivity p-n junction diode

Q5. As per Indian Electricity rule in overhead systems, the recommended span in case of RCC pole is….
(a) 40-50 meters
(b) 50-80 meters
(c) 80-100 meters
(d) 100-300 meters

Q6. A current wave is given by i = 4 + 2√2 sin 3θ + 4√2 sin 5θ. The r.m.s. value of current wave is ………
(a) 10 A
(b) 6 A
(c) √56 A
(d) 5 A

Q7. Domestic appliances are connected in parallel across a.c mains because ……….
(a) it is a simple arrangement
(b) operation of each appliance becomes independent of the other
(c) appliances have same current ratings
(d) this arrangement occupies less space

Q8. In 3-phase induction motor maximum torque is inversely proportional to the
(a) Speed of rotor
(b) Stator voltage
(c) Decreasing slip speed
(d) dRotor reactance

Q9. A centrifugal switch is provided for disconnecting the auxiliary winding in a
(a) Capacitor start motor
(b) Capacitor run motor
(c) Hysteresis motor
(d) Reluctance motor

Q10. The ratio of primary to secondary voltages is 2:1. The saving in terms of weight of copper required if an autotransformer is used instead of a two-winding transformer will be:
(a) 33.3 %
(b) 50 %
(c) 66.7 %
(d) 95 %

SOLUTIONS
S1. Ans.(a)
Sol. An overhead transmission line is provided with earth wire for protection against voltage surge due to direct lightning stroke.

S2. Ans.(b)
Sol. A lightning arrester:
>Provides low impedance path for surge current
>Is connected in parallel with the equipment under protection.

S3. Ans.(d)
Sol. Zener diode is used as a Shunt voltage regulator for regulating voltage across small loads. The breakdown voltage of Zener diodes will be constant for a wide range of current. Zener diode is connected parallel to the load to make it reverse bias and once the Zener diode exceeds knee voltage, the voltage across the load will become constant.

S4. Ans.(c)
Sol. A tunnel diode:
>Heavily doped two-terminal P-N junction
>Exhibits negative resistance characteristics
>Voltage controlled device
>Due to heavy doping, depletion region is narrow.
>High conductivity

S5. Ans.(c)
Sol. RCC poles: span=80-100 meters
Line support :Recommended span
Wooden pole: 40-50 meters
Steel pole :50-80 meters
RCC pole :80-100 meters
Steel tower :300 meters or above

S6. Ans.(b)
Sol. Ir.m.s. = √((4)^2+(2)^2+(4)²) = 6A

S7. Ans.(b)
Sol. Home appliances are connected in parallel to provide equal supply voltage to all. secondly, if one appliance is removed it would not affect the condition of others. in series if one appliance is open the complete circuit would be open.

S8. Ans.(d)
Sol. In 3-phase induction motor: T_(max ) α 1/X_2

S9. Ans.(a)
Sol. In case of capacitor start motor, a centrifugal switch is provided for disconnecting the auxiliary winding when the motor attains speed up-to 70-80% of synchronous speed.

S10. Ans.(b)
Sol. Here, a=2
∴ Cu saving=1/a=1/2=0.5=50%

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