MCQ on Electrical Measuring Instruments with Answers

21. Permeameters are essentially pieces of apparatus constructed for testing of

(a) magnetic specimens in the form of bars.
(b) magnetic specimens in the form of rings.
(c) magnetic specimens both in the form of bars and rings.
(d) none of the above.

22. Ballistic tests are used in magnetic measurements for determination of

(a) B-H curve of a specimen.
(b) hysteresis loop of a specimen.
(c) flux density, magnetic force of B-H curve and hysteresis loop of the specimen.
(d) finding out losses in the specimen.

23. Iron losses in a magnetic specimen can be measured by using

(a) Campbell bridge method.
(b) Anderson bridge method.
(c) Hay bridge method.
(d) Schering bridge method.

24. Sphere gap is used for measurement of

(a) peak value of radio frequency voltage.
(b) insulation resistance in capacitance divider.
(c) peak value of power frequency voltages.
(d) fast rising transient voltage.

25. Impulse voltages are characterized by

(a) polarity.
(b) peak value.
(c) time of half the peak value.
(d) all of the above.

26. Which of the following statements about impulse voltage is true ?

(a) An impulse voltage is a unidirectional voltage.
(b) In chopped impulse voltage, flash-over does not occur.
(c) Time taken to rise is exactly equal to the time taken to fall.
(d) RMS value of impulse voltage is always less than 50% of average value.

27. The insulating oil, fit for use, should withstand

(a) at least 20 kV for two minutes.
(b) at least 40 kV for one minute.
(c) at least 100 kV for one minute.
(d) at least 200 kV for half minute.

28. A Schering bridge used for testing of a porcelain insulator should be shielded by a metallic screen so that

(a) no crack develops in the insulator during testing.
(b) Earth’s magnetic field does not affect it.
(c) it is safe for the operator.
(d) external electrostatic field does not affect it.

29. The sensitivity of a photodiode depends upon

(a) light intensity and depletion region width.
(b) depletion region width and excess carrier life time.
(c) excess carrier life time and forward bias current.
(d) forward bias current and light intensity.

30. A photocell is illuminated by a small-bright source placed 1 m away. When the same source of light is placed 2 m away, the electrons emitted by the photocathode

(a) each carry one-quarter of their previous energy.
(b) each carry one-quarter of their previous moments.
(c) are half as numerous.
(d) are one quarter as numerous.

31. Which one of the following statements is correct ? An electronic voltmeter is more reliable as compared to multimeter for measuring voltages across low impedance because

(a) its sensitivity is high.
(b) it offers high input impedance.
(c) it does not alter the measured voltage.
(d) its sensitivity and input impedance are high and do not alter the measured value.

32. The essential elements of an electronic instrument is a/an

(a) transducer.
(b) signal conditioner.
(c) indicating device.
(d) all of the above.

33. Electronic voltmeter provides more accurate readings in high resistance circuits as compared to non-electronic voltmeter because of its

(a) high V/ohm ratings.
(b) high ohm/V ratings.
(c) low meter resistance.
(d) high resolution.

34. An advantage which a VTVM has over a non-electronic voltmeter is

(a) low power consumption.
(b) low input impedance.
(c) the ability to measure wider ranges of voltage and resistance.
(d) greater portability.

35. VTVM can be used to measure

(a) dc voltage.
(b) ac voltage of high frequency.
(c) dc voltage and ac voltage upto the order of 5 MHz frequency.
(d) ac voltage of low frequency.

36. Which of the following are the advantages of a balanced bridge vacuum tube voltmeter in comparison with a conventional VTVM?

1. Higher input impedance.
2. Effect of changes due to variation in valve characteristics is minimized.
3. Power supply fluctuations have less effect on measurement.

Select the correct answer using the code given below :
(a) 1 and 2.
(b) 2 and 3.
(c) 2 and 3.
(d) 1, 2 and 3.

36. A dc VTVM can be used for measuring voltages of frequency up to about 250 MHz with the help of

(a) rectifier.
(b) RF probe.
(c) RC circuit.
(d) LC circuit.

38. In modem electronic multimeters, a FET or MOSFET is preferred over BJT, because

(a) its input resistance is high.
(b) its input resistance is high and does not vary with the change of range.
(c) its input resistance is low.
(d) it is cheaper.

39. The function of input attenuators in
measuring instruments like VTVM, CRO etc. is to

(a) increase the input impedance.
(b) attenuate the frequency range.
(c) attenuate the input signal amplitude without altering the frequency contents.
(d) attenuate the input impedance.

40. The effective value of a complex waveform should be measured with a voltmeter which responds to

(a) peak.
(b) true rms.
(c) average.
(d) peak-to-peak value.