Quiz: Electrical Engineering 17 Aug 2020

Quiz: Electrical Engineering
Exam: NLC-GET
Topic: Miscellaneous

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

Q1. In ……………, the susceptibility will decrease with increase in temperature and they have relatively small susceptibility at all temperatures.
(a)Anti-ferromagnetic materials
(b)Ferrimagnetic materials
(c)Superparamagnetic materials
(d)Ferromagnetic materials

Q2. In which of the following motors is torque produced due to the tendency of the rotor to align itself in the minimum reluctance position when the speed of the motor is close to the synchronous speed?
(a)Hysteresis motor
(b)Repulsion motor
(c)Reluctance motor
(d)Universal motor

Q3. For ………., the output C(s) of the system is equal to transfer function of the system.
(a)Impulse response
(b)Step response
(c)Parabolic response
(d)Ramp response

Q4. The function of the ………… is to facilitate collection of current from the armature conductors.
(a)Yoke
(b)Commutator
(c)Pole
(d)Brush

Q5. High resistances are provided with a guard terminal. This guard terminal used to:
(a)To eliminate the effect of leads
(b)Guard the resistance against stray electrostatic fields
(c)Bypass the leakage current
(d)Guard the resistance against overloads

Q6. If A is the number of parallel paths and P is the number of poles, then the number of parallel paths in lap winding and in wave winding is
(a) A = P, A = 2
(b) A = 2P, A = P
(c) A = 2, A = P
(d)A = P, A = 2P

Q7. In a d.c. machine, the current rating and voltage rating of wave winding is
(a) Low, high
(b) High, low
(c) High, high
(d) Low, low

Q8. A forward bias PN junction will act as a/an:
(a)Amplifier
(b)Open switch
(c)Closed Switch
(d)Attenuator

Q9. A single phase 230V energy meter has a constant load of 5 A passing through it for 6 hours at unity p.f. If the meter disc makes 2070 revolutions during this period, what is the meter constant in revolutions per unit?
(a) 100 rev/unit
(b) 200rev/unit
(c) 300rev/unit
(d) 400rev/unit

Q10. Resistance of an ammeter having range 0–5A is 1.8 Ω. It is shunted by a resistor of
0.2 Ω. What is the effective current when the pointer reads 2 A?
(a) 10 A
(b) 30 A
(c) 15 A
(d) 20 A

SOLUTIONS

S1. Ans.(a)
Sol. Antiferromagnetic materials have small positive susceptibilities at all temperatures. A critical temperature in this case is called Neel temperature. The material’s susceptibility changes around the Neel temperature as shown in fig. given below. The susceptibility increases inversely with temperature above TN and decreases inversely below this temperature.

S2. Ans.(c)
Sol. The reluctance motor has basically two main parts called stator and rotor. the stator has a laminated construction, made up of stampings. in the reluctance motor, rotor tries to align itself with the axis of rotating magnetic field in a minimum reluctance position. But due to rotor inertia, it is not possible, when rotor is in standstill condition.
So, rotor starts rotating near synchronous speed as a squirrel cage induction motor. When the rotor speed is about synchronous, stator magnetic field pulls rotor into synchronism i.e. minimum reluctance position and keeps it magnetically locked. Then rotor continues to rotate with a speed equal to synchronous speed. Such a torque exerted on the rotor is called the reluctance torque.

S3. Ans.(a)
Sol. For impulse response, the output C(s) of the system is equal to transfer function of the system.

S4. Ans.(b)
Sol. Functions of commutator in d.c. machines are:
(A) To facilitate the collection of current from armature conductors
(B) To convert internally developed induced emf to unidirectional emf
(C) To produce unidirectional torque in case of motors

S5. Ans.(c)
Sol. The guard terminal used to bypass the leakage current. Current flowing into the guard terminal is not measured by the instrument and so is ignored by the insulation resistance measurement.

S6. Ans.(a)
Sol. number of parallel paths for LAP winding: A = P
Number of parallel paths for wave winding: A = 2

S7. Ans.(a)
Sol. wave winding is used for HIGH VOLTAGE and low current rating applications.

S8. Ans.(c)
Sol. If the positive terminal of an external battery is connected to p-type and its negative terminal to n-type of PN junction then such a biasing called forward biasing.
An ideal diode acts as a short circuit or closed switch under forward bias condition and open circuit or open switch under reverse biased condition.

S9. Ans.(c)
Sol. Meter constant (k) =(No.of revolution)/(Energy in given period)
=2070/VIcosϕ(t) and (t)→ in hours
=2070/(230×5×1×6)
=2070/6.9=300 rev\/kwh
= 300 rev/unit

S10. Ans.(d)
Sol. Multiplying power of shunt, m=Rm/Rsh +1=1.8/0.2+1=10
Therefore, the range of ammeter increases 10 times. When the ammeter indicates 2 A, the circuit current = 2 ×10 = 20 A.

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