Quiz: Electrical Engineering 15 Oct 2020

Quiz: Electrical Engineering
Exam: SSC-JE
Topic: Measurement and measuring instrument

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

Q1. Watt-hour meter is classified as a
(a) Recording instrument
(b) Deflecting instrument
(c) Integrating instrument
(d) Indicating instrument

Q2. A PMMC meter rated at 200 µA is used in a rectifier type instrument which uses full wave rectification. What is the sensitivity on sinusoidal AC?
(a) 9 KΩ/V
(b) 4.5 KΩ/V
(c) 18 KΩ/V
(d) 10 KΩ/V

Q3. The bridge suitable for the measurement of an unknown inductance in terms of known capacitance would include
(a) Maxwell and Schering
(b) Maxwell and Hay
(c) Hay and Schering
(d) Maxwell, Hay and Schering

Q4. If an energy meter disc makes 40 revolutions in 50 sec when a load of 5 KW is connected to it, the meter constant (in rev/kw-h) is:
(a) 500
(b) 1000
(c) 480
(d) 576

Q5. The current and potential coils of a dynamometer type wattmeter were accidentally interchanged while connecting. After energizing the circuit, it was observed that the wattmeter did not show the reading. This could be due to the
(a) Damage to current coil
(b) Damage to potential coil
(c) Loose contacts
(d) Damage to both the potential and current coil

Q6. The voltage coil of a single-phase house service energy meter
(a) Is highly capacitive
(b) Is highly resistive
(c) Is highly inductive
(d) None of the above

Q7. Consider the following types of damping:
1. Air-friction damping
2. Fluid-friction damping
3. Eddy current damping
PMMC types instruments use which of the above?
(a) 1 only
(b) 2 only
(c) 3 only
(d) 1, 2 and 3

Q8. The correct statement about Electrodynamometer instrument amongst the following is:
(a) Its scale in linear
(b) It measures only DC
(c) It is a transfer instrument
(d) Its sensitivity is less than M.I. type instruments

Q9. The type of instruments used mainly for standardizing instruments in laboratories is
(a) Indicating instrument
(b) Integrating instrument
(c) Absolute instrument
(d) Recording instrument

Q10. A 0-200 V voltmeter has an accuracy of 0.75% of full-scale reading. If voltage measured is 100 V, the error is:
(a) 3%
(b) 2%
(c) 1.5%
(d) .75

SOLUTIONS
S1. Ans.(c)
Sol.
Indicating Instrument – The instrument which indicates the magnitude of the measured quantity is known as the indicating instrument.
e.g. ammeter, voltmeter
Integrating Instrument – The instrument which measures the total energy supplied at a particular interval of time is known as the integrating instrument. The total energy measured by the instrument is the product of the time and the measures electrical quantities.
e.g. energy meter, watt-hour meter
Recording Instrument – The instrument records the circuit condition at a particular interval of time is known as the recording instrument.
Deflecting instrument: The instrument in which the deflection provides the basis for measuring the electrical quantity is known as the deflection type instrument.
E.g. PMMC type ammeter

S2. Ans.(b)
Sol. sensitivity is reciprocal of full-scale deflection (I_FSD).
∴S_DC=1/I_FSD =1/(200×10^(-6) )=5 KΩ/V
For full-wave rectification, AC sensitivity=0.9×DC sensitivity
∴S_AC=0.9×5=4.5 KΩ/V

S3. Ans.(b)
Sol. maxwell and hay’s bridge are used to find the value of self-inductance.
Schering bridge is used to measure the capacitance.

S4. Ans.(d)
Sol. No. of revolutions in one hour=(40×3600)/50=2880
∴meter constant(k)=(no of revolutions)/(kili-watt hours)=2880/5=576 rev/kw-h

S5. Ans.(a)
Sol. current coil is connected in series and carries the load current. If both coils are interchanged then current coils gets directly connected across the supply and large current flows through the coil resulting into damage to current coil.

S6. Ans.(c)
Sol. The voltage coil of a single-phase house service energy meter is highly inductive.

S7. Ans.(c)
Sol. PMMC types instruments use eddy current damping.

S8. Ans.(c)
Sol. Transfer instrument: – Any instrument which is calibrated with DC source and used without any modification for AC measurements. Such a transfer instrument having same accuracy for both DC and AC.
E.g.: – Dynamometer.
(Td ⍺ I^2 orV^2 )
So, for dynamometer instruments: –
I. Scale is non-uniform
II. It is a transfer instrument
III. Coils are air-cored

S9. Ans.(c)
Sol. Standardizing instruments: – use for scrutinizing the accuracy of a measuring instrument by comparing it with a standard instrument.

S10. Ans.(c)
Sol. ▭( limiting error=(%Accuracy×FSD)/(True value (AT) ))
=(0.75×200)/100
=1.5%

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