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NHPC-JE’21 EE: Daily Practices Quiz 08-Oct-2021

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NHPC-JE’21 EE: Daily Practices Quiz

NHPC-JE’21 EE: Daily Practices Quiz 08-Oct-2021

Each question carries 1 mark.
Negative marking: 1/4 mark
Total Questions: 06
Time: 06 min.

Q1. Which part of DC machines converts the alternating current induced in armature conductors into unidirectional current in the external load circuit?
(a) Pole coils
(b) Commutator
(c) Armature windings
(d) Armature core

Q2. Power transformers are generally designed to have maximum efficiency around
(a) No load
(b) Half load
(c) Near full load
(d) None of the above

Q3. Thin laminations are used in a machine in order to reduce
(a) Eddy current losses
(b) Hysteresis losses
(c) Both a and b
(d) None of the above

Q4. Which of the following theorems can be applied to any network linear or non-linear, active or passive, time-variant or time-invariant?
(a) Norton theorem
(b) Thevenin theorem
(c) Superposition theorem
(d) Tellegen theorem

Q5. The bandwidth of an AC series circuit consisting of R, L & C is
(a) L/RC
(b) RC/L
(c) R/L
(d) L/R

Q6. Which of the following statement is true?
(a) At higher voltage, cost of transmission is reduced
(b) At higher voltage, cost of transmission is increased
(c) Both a and b
(d) None of the above

SOLUTIONS

S1. Ans.(b)
Sol. The commutator will convert AC to DC in DC generators and vice versa in DC motors.
In the generator, the main function of the commutator is to facilitate the collection of current from the armature conductors and to convert the alternating emf induced (AC) in the armature conductors to unidirectional emf (DC) in the external load circuit.
In the motor, the main function of the commutator is to supply current to armature from the external DC circuit and to convert this unidirectional emf (DC) of the external DC circuit to alternating emf in the armature.

S2. Ans.(c)
Sol. Power transformers are generally designed to have maximum efficiency near full load, whereas distribution transformers have maximum efficiency at 50% of full load.

S3. Ans.(a)
Sol. Thin laminations are used in order to reduce the eddy current losses only. Due to laminations the area of the eddy currents loops is minimized and the losses due to eddy current losses are minimized.

S4. Ans.(d)
Sol. Tellegen theorem can be applied to any network linear or non-linear, active or passive, time-variant or time-invariant.

S5. Ans.(c)
Sol. The bandwidth of an AC series circuit consisting of R, L & C: BW=R/L

S6. Ans.(a)
Sol. At higher voltage, the volume of the conductor is reduced. Area of conductor A ∝ 1/Vs² Where Vs = Supply voltage. So that material requirement is reduced and hence cost of the material and transmission is reduced.

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