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NHPC-JE’21 EE: Daily Practices Quiz 14-Dec-2021

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NHPC-JE’21 EE: Daily Practices Quiz

NHPC-JE’21 EE: Daily Practices Quiz 14-Dec-2021

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

Q1. The magnetic field required to reduce the residual magnetism to zero is called
(a) Hysteresis
(b) Retentivity
(c) Coercivity
(d) none of these

Q2. The thermal efficiency and electrical efficiency of a steam power station are 30% and
92% respectively. The overall efficiency of the station is
(a) 55.8%
(b) 27.6%
(c) 62.8%
(d) 45%

Q3. Condition for maximum power delivered in D.C. Generator is_______:
(a) Back EMF = (2 × Supply voltage)
(b) Back EMF = Supply voltage
(c) Back EMF = (Supply voltage/4)
(d) Back EMF = (Supply voltage/9)

Q4. Under-commutation gives rise to …….
(a) sparking at the leading edge of the brush
(b) sparking at the trailing edge of the brush
(c) no sparking at all
(d) sparking at the middle of the brush

Q5. An electrodynamometer type of instrument finds its major use as
(a) standard instrument only
(b) transfer instrument only
(c) both as standard and transfer instruments
(d) an indicator type of instrument

Q6. Moving coil meter is used to measure only
(a) D.C.
(b) A.C.
(c) D.C. and A.C.
(d) None of these


S1. Ans.(c)
Sol. from the B-H curve, the value of magnetizing field requires to reduce residual magnetism to zero is called coercivity of the material.
RETENTIVITY: The value of the intensity of magnetization of a material when the magnetizing field is reduced to zero is called retentivity.

NHPC-JE'21 EE: Daily Practices Quiz 14-Dec-2021_20.1

S2. Ans.(b)
Sol. Overall efficiency = Thermal Efficiency × Electrical efficiency
= 0.30 × 0.92 = 0.276 or 27.6%

S3. Ans.(a)

NHPC-JE'21 EE: Daily Practices Quiz 14-Dec-2021_30.1

S4. Ans.(b)
Sol. Due to under–commutation, the flux at trailing edges gets crowded, so there is sparking.

S5. Ans.(c)
Sol. The electrodynamometer type instrument is a transfer instrument. A transfer instrument is one that is calibrated with a dc source and used without any modifications for ac measurements. Such a transfer instrument has same accuracy for ac and dc measurements. The electrodynamometer-type instruments are often used in accurate ac voltmeters and ammeters, not only at the power line frequency but also in the lower audio frequency range. With some little modifications, it can be used as a wattmeter for the power measurements.

S6. Ans.(a)
Sol. moving coil instruments used as DC ammeter and DC voltmeter.

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