Quiz: Electrical Engineering
Topic: Measurement and measuring instrument
Each question carries 1 mark.
Negative marking: 1/4 mark
Time: 10 Minute
Q1. Permanent-magnet moving coil instrument can be used for………………
(a) a.c. work only
(b) d.c. work only
(c) both d.c. and a.c. work
(d) none of the above
Q2. A moving coil instrument having meter resistance of 5Ω is to be used as a voltmeter of range 0-100 V. If the full-scale deflection current is 10 mA, then required series resistance is………….
(d) None of these
Q3. Megger is an instrument by which we can measure
(a) high resistance
(b) low resistance
(c) high current
(d) high voltage
Q4. The pressure coil of an energy meter is…….
(a) Purely resistive
(b) Purely inductive
(c) Highly resistive
(d) Highly inductive
Q5. The AC bridge used for measurement of dielectric loss of capacitor is
(a) Anderson bridge
(b) Schering bridge
(c) Wien bridge
(d) Hay’s bridge
Q6. Consider the following types of damping:
- Air-friction damping
- Fluid-friction damping
- 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
Q7. 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
Q8. The type of instruments used mainly for standardizing instruments in laboratories is
(a) Indicating instrument
(b) Integrating instrument
(c) Absolute instrument
(d) Recording instrument
Q9. A 0-200 V voltmeter has an accuracy of 0.75% of full-scale reading. If voltage measured is 100 V, the error is:
Q10. A voltmeter must have very high internal resistance so that
(a) Accuracy is high
(b) Resolution is high
(c) Draws small amount of current
(d) Creates high loading effect of the circuit
Sol. Permanent-magnet moving coil instrument can be used for dc work only.
Sol. Series resistance,
Rs=V/Im -Rm=(100 V)/(10 mA)-5=10000-5=9995Ω
Sol. The two instruments you will use most often to check continuity, or to measure the resistance of a circuit or circuit component, are the OHMMETER and the MEGGER (MEGOHMMETER). The ohmmeter is widely used to measure resistance and to check the continuity of electrical circuits and devices. Its range usually extends to only a few megohms. The megger is widely used for measuring insulation resistance, such as that between a wire and the outer surface of its insulation, and the insulation resistance of cables and insulators. The range of a megger can be extended to more than 1,000 megohms.
Sol. The pressure coil of an energy meter is highly inductive while for wattmeter it is highly resistive.
Sol. Schering bridge is used for measurement of dielectric loss of capacitor.
Sol. PMMC types instruments use eddy current damping.
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
Sol. Standardizing instruments: – use for scrutinizing the accuracy of a measuring instrument by comparing it with a standard instrument.
The use of absolute instruments is merely confined within laboratories as standardizing instruments.
Sol. ▭( limiting error=(%Accuracy×FSD)/(True value (AT) ))
Sol. voltmeter having high internal resistance so it draws low current and correctly measure the potential difference connected across the point a-b.