This Portion of Electrical andElectronic Measurements and Measuring instruments contains Measurement of Resistance MCQs (Multiple Choice Questions and Answers) / Objective Type Questions and Answers.

This Section covers below lists of topics.

  1. Classification of Resistances
  2. Measurement of Medium Resistances
  3. Measurement of Low Resistance
  4. Measurement of High Resistances
  5. Measurement of Earth Resistance
  6. Localization of Cable Faults

PRACTICE IT NOW TO SHARPEN YOUR CONCEPT AND KNOWLEDGE

1. A resistance of value 10Ω approximately is to be measured by ammeter-voltmeter method with resistance of ammeter is 0.02Ω and that of voltmeter is 5000Ω. The resistance should be measured

  • By connecting the ammeter on the side of unknown resistance as this connection gives better accuracy
  • By connecting the voltmeter on the side on unknown resistance as this connection gives better accuracy
  • By any of the two connections, as both of them give equal accuracy
  • None of the above.

2. A unknown resistance is measured by substitution method. First a standard known resistance of 100 Ω is connected in series with a circuit having a rheostat and a galvanometer. The battery voltage is 10V and the setting of rheostat is 500 Ω and the galvanometer shows a deflection of 60°. After this test. The battery voltage goes down to 9 V and when the unknown resistance is substituted for the known resistance, the galvanometer again shows a deflection of 60° with the same setting of the rheostat. The value of unknown resistance is :

  • 100 Ω
  • 54 Ω
  • 90 Ω
  • None of the above.

3. Equal resistance of 100 Ω each are connected in each arm of wheatstone bridge which is supplied by 2 V  battery source. The galvanometer of negligible resistance connected to the bridge can sense as low current as 1 µA. the smallest value of resistance that can be measured is

  • 20 µΩ
  • 2 µΩ
  • 30 µΩ
  • None of the above.

4. A wheatstone bridge has ratio arms of 1000Ω and 100Ω resistance, the standard resistance arms consists 4 decades resistance boxes of 1000,100,10 ,1 Ω steps. The maximum and minimum value of unknown resistance which can be determined with this set up is

  • 111100Ω, 1Ω
  • 11110Ω, 10Ω
  • 111100Ω, 10Ω
  • None of the above.

5. A wheatstone bridge can not be used for precision measurements because errors are introduced into on account of

  • Resistance of connecting leads
  • Thermo-electric emfs
  • Contact resistances
  • All the above.

6. A Kelvin-varley slide consists of 4 decade dividers. The first decade is constructed by having 11 coils of 10 kΩ resistance each. The subsequent decades will have coils of :

  • 11 coils of 20 kΩ each, 11 coils of 40 kΩ each, 11 coils of 80 kΩ each
  • 11 coils of 10 kΩ each, 11 coils of 5 kΩ each, 10 coils of 1 kΩ each
  • 11 coils of 2 kΩ each, 11 coils of 400 Ω each, 11 coils of 80 Ω each
  • 11 coils of 2 kΩ each, 11 coils of 400 Ω each, 10 coils of 80 Ω each

7. Low resistance are provided with four terminals

  • To facilitates the connection of current and potential circuits
  • In order that the resistance value becomes definite irrespective of the nature of contacts at the terminals
  • To eliminate the effect of thermo-electric emfs
  • To eliminate the effect of leads

8. In a kelvin’s double bridge two sets of readings are taken when measuring a low resistance, one with the current in one direction and the other with the direction of the current reversed. This is done to :

  • Eliminate the effect of contact resistance
  • Eliminate the effect of resistance of leads
  • Correct for changes in battery voltages
  • Eliminate the effect of thermo-electric emfs.

9. High resistances are provided with a guard terminal.This guard terminal is used to :

  • Bypass the leakage current
  • Guard the resistance against stray electrostatic fields
  • Guard the resistance against overloads
  • None of the above.

10. When measuring insulation resistance of cables using d.c sources, the galvanometer used should be initially short circuited because .

  • Cables have a low value of initial resistance
  • Cables have a high value of capacitance which draws high value of charging current
  • Cables have a low value of capacitance which draws high value of charging current
  • None of the above.

11. A circular peice of specimen has a surface resistance Rs. its diameter is d and the thickness is t. the surface resistivity ps of the specimen is given by :

  • (πd2 Rs)/t
  • (πdRs)/t
  • Rst/(πd2)
  • Rs)t/πd

12. The value of resistance of an earthing electrode depends upon :

  • Shap and materials of electrode
  • Depth to which electrode is driven into earth.
  • Specific resistance of soil
  • All the above.

13. From the point of view of safety, the resistance of earthing electrode should be :

  • Low
  • High
  • Medium
  • The value of resistance of earth electrodes does not affect the safety.

14. The advantage of Varley loop tests over Murray loop tests is

  • They can be used for localizing of short circuit faults
  • They can be used for localizing of earth fault
  • The loop resistance can be experimentally determined
  • Their accuracy is higher.

15. When localizing ground fault with the help of loop tests, the resistance of the fault :

  • Affects the balance conditions
  • Affects the value of capable resistance
  • Affects the sensitivity of the bridge
  • All the above.

16. In a series-type ohmmeter

  • zero marking is on the left-hand side
  • zero marking is at the centre
  • zero marking is on the right-hand side
  • zero marking may be either on left or right-hand side

17. In series type ohmmeters, zero adjustment should be done by

  • changing the shunt resistance across the meter movement
  • changing the series resistance
  • changing the series and the shunt resistance
  • changing the battery voltage

18. Screw adjustments are preferred over shunt resistance adjustments for zero calibration in ohmmeters because

  • the former method is less costly
  • the former method does not disturb the scale calibration
  • the former method does not disturb the meter magnetic field
  • all of the above

19. The shape of scale in an analog series-type ohmmeter is

  • linearly spaced
  • cramped near the start
  • cramped near the end
  • directly proportional to the resistance

20. Shunt-type ohmmeters have on their scale

  • zero ohm marking on the right corresponding to zero current
  • zero ohm marking on the right corresponding to full scale current
  • infinite ohm marking on the right corresponding to zero current
  • infinite ohm marking on the right corresponding to full scale current

21. Shunt-type ohmmeters have a switch along with the battery to

  • disconnect the battery when not in use
  • prevent meter from getting damaged when measuring very low resistances
  • compensate for thermo-emf effects by reversing battery polarity
  • all of the above

22. The shape of scale in an analog shunt-type ohmmeter is

  • linearly spaced at lower scales
  • cramped near the start
  • linearly spaced at higher scales
  • uniform all throughout the scale

23. High resistances using the voltmeter–ammeter method should be measured with

  • voltmeter connected to the source side
  • ammeter connected to the source side
  • any of the two connections
  • readings are to be taken by interchanging ammeter and voltmeter positions

24. Low resistances using the voltmeter–ammeter method should be measured with

  • voltmeter connected to the source side
  • ammeter connected to the source side
  • any of the two connections
  • readings are to be taken by interchanging ammeter and voltmeter positions

25. Accuracy of the substitution method for measurement of unknown resistance depends on

  • accuracy of the ammeter
  • accuracy of the standard resistance to which the unknown is compared
  • accuracy in taking the readings
  • all of the above

26. The null detector used in a Wheatstone bridge is basically a

  • sensitive voltmeter
  • sensitive ammeter
  • may be any of the above
  • none of (a) or (b)

27. Wheatstone bridge is not preferred for precision measurements because of errors due to

  • resistance of connecting leads
  • resistance of contacts
  • thermo-electric emf
  • all of the above

28. Error due to thermo-electric emf effects in a Wheatstone bridge can be eliminated by

  • taking the readings as quickly as possible
  • by avoiding junctions with dissimilar metals
  • by using a reversing switch to change battery polarity
  • all of the above

29. Low resistances are measured with four terminals to

  • eliminate effects of leads
  • enable the resistance value to be independent of the nature of contact at the current terminals
  • to facilitate connections to current and potential coils of the meters
  • all of the above

30. Kelvin’s double bridge is called ‘double’ because

  • it has double the accuracy of a Wheatstone bridge
  • its maximum scale range is double that of a Wheatstone bridge
  • it can measure two unknown resistances simultaneously, i.e., double the capacity of a Wheatstone bridge
  • it has two additional ratio arms, i.e., double the number of ratio arms as compared to a Wheatstone bridge

31. Two sets of readings are taken in a Kelvin’s double bridge with the battery polarity reversed in order to

  • eliminate the error due to contact resistance
  • eliminate the error due to thermo-electric effect
  • eliminate the error due to change in battery voltage
  • all of the above

32. Potentiometers, when used for measurement of unknown resistances, give more accurate results as compared to the voltmeter–ammeter method because

  • there is no error due to thermo-electric effect in potentiometers
  • the accuracy of voltage measurement is higher in potentiometers
  • personnel errors while reading a potentiometer is comparatively less
  • all of the above

33. Null detection method’ is more accurate than ‘deflection method’ for measurement of unknown resistances because

  • the former does not include errors due to nonlinear scale of the meters
  • the former does not include errors due to change in battery voltage
  • the former does to depend on meter sensitivity at balanced condition
  • all of the above
  • bypass the leakage current
  • guard the resistance from effects of stray electro-magnetic fields
  • guard the resistance from effects of stray electro-static fields
  • none of the above

35. When measuring cable insulation using a dc source, the galvanometer used is initially short circuited to

  • discharge the stored charge in the cable
  • bypass the high initial charging current
  • prevent the galvanometer from getting damaged due to low resistance of the cable
  • all of the above

36. The loss of charge method is used for measurement of

  • high value capacitances
  • dissipation factor of capacitances
  • low value resistances
  • high value resistances

37. A meggar is used for measurement of

  • low value resistances
  • medium value resistances
  • high value, particularly insulation resistances
  • all of the above

38. Controlling torque in a meggar is provided by

  • control springs
  • balance weights
  • control coil
  • any one of the above

39. The advantage of Varley loop test over Murray loop test for cable fault localisation is

  • the former can be used for localising faults even without knowledge of cable resistance
  • the former can be used for localising both earth fault and short circuit faults
  • the former can experimentally determine the total loop resistance
  • all of the above

40. Possible sources of error in using loop test for cable fault localisation are

  • uneven cable resistance/km
  • temperature variations
  • unknown cable joint resistances
  • all of the above

 

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