This Portion of Electrical andElectronic Measurements and Measuring instruments contains Analog Ammeters, Voltmeters and Ohmmeters MCQs (Multiple Choice Questions and Answers) / Objective Type Questions and Answers.

This Section covers below lists of topics.

1. Types of instruments
2. Errors in ammeters and voltmeters
3. Permanent magnet moving coil instruments (PMMC)
4. Ohmmeters
5. Multimeter or Volt-Ohm-Milli-Ammeter (V.O.M)
6. Ratiometer
7. Megger
8. Moving Iron (M.I) Instruments
9. Electrodynamometer (Electrodynamics) type of instruments
10. Electrothermic instruments
11. Hot wire Instruments
12. Thermocouple instruments
13. Electrostatic instruments
14. Rectifier type instruments

PRACTICE IT NOW TO SHARPEN YOUR CONCEPT AND KNOWLEDGE

#### 1. An hypothetical electrostatic voltmeter with spring control is designed with one fixed and another movable plate. Both plates are in the form of a circle with one plate over the other so as to produce a rotatary motion. If a voltage is applied between them, no rotatry motion is produced because :

• There is no change in the voltage
• The is no change in the capacitance irrespective of the relative position of the two plates
• The spring force is very large
• The applied voltage is small to produce any noticeable deflection.

#### 2. An electrostatic voltmeter draws a small value of current on d.c

• Under steady condition respective of the applied voltage
• When switched on irrespective of the applied voltage
• When measuring low voltages
• When measuring high voltages

#### 3. An Quadrant type electrostatic instrument uses two types of connections 1) heterostatic and 2)idiostatic An external battery is used

• For ideostatic connection
• For heterostatic connection
• For both ideostatic and hetrostatic connections
• None of the above.

#### 4. The size of electrostatic voltmeter is large as compared with that corresponding electro-magnetic voltmeters because :

• They are used for measurement of high voltages
• Energy density in an electrostatic field is considerably smaller than that in an electro-magnetic field
• Their frequency range is smaller
• They have high dielectric loss.

#### 5. The range of an electrostatic voltmeter can be extended by using :

• A capacitor in series with the voltmeter whose capacitance is greater than the capacitance of the voltmeter
• A capacitance in series with the voltmeter whose capacitance is smaller than the capacitance of the voltmeter
• A resistor in series with the voltmeter
• An inductor in series with the voltmeter.

• 10kΩ/V
• 9kΩ/V
• 4.5kΩ/V
• 22.2kΩ/V

• 20 kΩ/V
• 9 kΩ/V
• 22.2 kΩ/V
• 18 kΩ/V

#### 8. A reversed biased diode in addition to a forward biased diode is used in rectifier type voltmeters using half wave rectification. The use of reverse biased diode is

• It does not allow any current to flow through the meter during negative half cycle
• In short-circuits the meter during the negative half cycle
• It does not allow the reverse leakage current to flow through the meter during the negative half cycle
• All of the above

#### 9. The PMMC meter used in rectifier type voltmeters are provided with shunts even at the expense of lowering sensitivity. Why?

• The shunting of the meter causes the circuit current to be high thereby making the rectifier work in the linear portion of its v-I characteristics.
• The shunt prevents meter against sudden overload
• The provision of shunt increases the sensitivity of the circuit
• All the above.

#### 10. Why are multimeters provided with separate scale for low a.c voltages?

• To improve the readability of the scale.
• To have high accuracy
• d. None of the above.

#### 11. Which meter has the highest accuracy in the prescribed limit of frequency range:

• PMMC
• Moving iron
• Electrodynamometer
• Rectifier

#### 12. Which instrument is the cheapest disregarding the accuracy

• PMMC
• Moving iron
• Electrodynamometer
• Rectifier

#### 13. Which instrument has the highest frequency range with accuracy within reasonable limits

• Moving iron
• Electrodynamometer
• Thermocouple
• Rectifier

#### 14. A Voltmeter has a resistance of 2000Ω. When it is connected across a d.c circuit its power consumption is 2 mW. Suppose this voltmeter is replaced by a voltmeter of 4000 Ω resistance, the power consumption will be ________ The circuit condition remains undisturbed.

• 4 mW
• 1 mW
• 2 mW
• None of the above.

#### 15. A milliammeter of resistance 100Ω is connected in series with a circuit. Its power consumption is 0.1 mW. Supposing it is replaced with a milliammeter of 200Ω resistance the power consumption will be

• 0.2 mW
• 0.05 mW
• 0.1 mW
• None of the above.

#### 16. The high torque to weight ratio in an analog indicating instrument indicates:

• High friction loss
• Low friction loss
• Nothing as regards friction loss
• None of the above.

• 180°
• 90°
• 45°
• 135°

• 0.001 Ω
• 0.1001 Ω
• 100000 Ω
• 100 Ω

#### 19. Swamping resistance is connected

• In series with the shunt to reduce temperature error in shunted ammeters
• In series with the ammeter to reduce errors on account of friction
• In series with meter and have a high resistance temperature co-efficient in order to reduce temperature errors in ammeters
• In series with the meter and have a negligible resistance co-efficient in order to reduce temperature errors in shunted ammeters.

#### 20. In order to reduce errors on account of temperature, instruments are provided with shunts use series connected swamping resistance. In order that errors on account temperature changes be low, the swamping resistance

• Should be made of a material having a high resistance temperature co-efficient
• Should be made of material having a low resistance temperature co-efficient with the value of swamping resistance equal to meter resistance
• Should be made of materials having low resistance temperature co-efficient and should have a value of about 20 to 30 times that of meter resistance.
• Should have an infinite value

#### 21. A 4-range milliammeter having ranges of 0-10 mA, 0-50 mA, 0-100mA and 0-500 mA. It is used for measurement of current whose magnitude is not known. In order to prevent damage to the instrument, the selector switch of the ammeter should be first placed at

• 0 – 50 mA range
• 0 – 100 mA range
• 0 – 10 mA range
• 0 – 500 mA range.

• 999Ω
• 9999Ω
• 9900 Ω
• 990 Ω

#### 23. A d’Arsonval movement is rated at 50 µA. its sensitivity is

• 20000 Ω/V
• 200000 Ω/V
• 200 Ω/V
• Can not be determined.

#### 24. A d’Arsonval movement has a sensitivity of 40,000 Ω and its internal resistance is 4000 Ω. The resistance of multiplier to convert it to 1V voltmeter is :

• 44000 Ω
• 36000 Ω
• 3600 Ω
• None of the above.

#### 25. A PMMC instrument is spring controlled. The control spring stiffness decreases by about 0.04 percent per °C rise in temperature and the strength of magnets goes down by 0.02 percent per °C rise in temperature. The rise in temperature is 10 °C the deflection

• Decreases by about 0.2 percent
• Decreases by about 0.4 percent
• Increases by about 0.4 percent
• Increases by about 0.2 percent.

#### 26. The power consumption PMMC instrument is typically about :

• 0.25 W to 2 W
• 0.25 mW to 2 mW
• 25 µW to 200 µW
• None of the above.

#### 27. In a series type ohmmeter :

• 0 marking is on the left hand side of side while ∞ marking is on the right hand side
• 0 marking is on the right hand side of scale and ∞ marking is on the left hand side
• Any of the above two markings can be on left or right side of the scale
• 0 marking is in the middle of scale.

#### 28. In a series type of ohmmeter the zero adjustment should be done

• By changing the value of series resistance
• By changing the value of shunt resistance connected across meter movement
• By changing both series as well as shunt resistance
• By changing the battery voltage.

• 62.5 Ω
• 2700 Ω
• 55 Ω
• 130 Ω

#### 30. A make break switch is provided to disconnect the battery when the meter is not in use in

• Both series and shunt type ohmmeters
• Only in series type ohmmeters
• Only in shunt type ohmmeters
• None of the above.

#### 31. A meggar is used for measurement of

• Low valued resistances
• Medium valued resistances
• High valued resistances, particularly insulation resistance
• All the above.

#### 32. The controlling torque in a meggar is provided by :

• Springs
• Weights attached to the moving system
• It does not need any controlling torque
• None of the above.

#### 33. A moving iron instrument can be used for current and voltage measurements

• In a.c circuits only
• In d.c circuits only
• In both a.c and d.c circuits for any value of frequency (in case of a.c circuits)
• In both a.c and d.c circuits for frequencies up to about 125 Hz (in case of a.c circuits).

#### 34. In spring controlled moving iron instruments, the scale is :

• Uniform
• Cramped at the lower end and expanded at the upper end
• Expanded at the lower end and cramped at the upper end
• Cramped both at the lower and the upper ends.

#### 35. Moving iron type of instrument can be used as :

• Standard instrument for calibration of other instruments
• Transfer type instruments
• Indicator type instruments as on panels
• All the above.

#### 36. Moving iron instruments when measuring voltage or currents

• Indicates the same values of measurand for both ascending and descending values
• Indicate higher value of measurand for descending values
• Indicate higher value of measurand for descending values
• None of the above.

#### 37. The moving iron voltmeters indicate :

• The same value for d.c and a.c voltages
• Lower values for a.c voltages than for corresponding d.c voltages
• Higher values for a.c voltages than for corresponding d.c voltages
• None of the above.

#### 38. A moving iron voltmeter reads low for a.c voltages than for corresponding values of d.c voltages. The meter can made to read equally for both a.c and d.c voltages

• If the resistance of the multiplier is made very high
• If the inductance of coil is made small
• If the resistance of the coil is made very large
• If the multiplier resistance is shunted by a capacitor of appropriate value to make the circuit non-inductive.

#### 39. Horizontally mounted moving iron instruments use :

• Eddy current damping
• Electromagnetic damping
• Fluid friction damping
• Air friction damping.

#### 40. The reason why eddy current damping cannot be use in moving iron instrument is :

• They have strong operating magnetic field
• They are not normally used in vertical position
• The need a large damping force which can only be provided by air friction
• They have very weak operating magnetic field and introduction of permanent magnet required for eddy current damping would distort the operating magnetic field.

#### 41. The frequency range of  moving iron instrument is

• Audio frequency band 20 Hz to 20 kHz
• Very low frequency band 10 Hz to 30 kHz
• Low frequency band 30 Hz to 300 kHz
• Power frequencies 0 to 125 Hz.

#### 42. Spring controlled moving iron instruments exhibits a square law response resulting in a non-linear scale. The shape of the scale can be made almost linear by :

• Keeping rate of change of inductance L with deflection ,1/Φ(dl/dΦ), as constant
• Keeping 1/KΦ as constant
• Keeping 1/KΦ as constant where K is the spring constant
• Φ (dl/dΦ), as constant

#### 43. An electrodynamometer type of instruments finds its major use as :

• Standard instrument only
• Transfer instrument only
• Both as standard and transfer instrument
• An indicator type of instrument.

• 1 Wb/m2
• 0.5 Wb/m2
• 0.05 Wb/m2
• 0.005 Wb/m2

#### 45. An Astatic movement in an electrodynamometer type of instrument is used for :

• Eliminating errors on account of external magnetic fields
• Increasing the operating torque of the instruments
• Providing eddy current damping
• None of the above.

#### 46. In order that an electrodynamometer type of instrument exhibits a pure square law response, the meter range should be limited to :

• - 45° to +45° about the position for zero mutual inductance between fixed and moving coils
• - 45° to +45° about the position for maximum mutual inductance between fixed and moving coils
• – 22.5° to +22.5° about the position for zero mutual inductance between fixed and moving coils
• - 90° to +90° about the position for maximum mutual inductance between fixed and moving coils

#### 47. A Voltage of 200 V at 5 Hz is applied to an electrodynamometer type of instrument which is spring controlled. The indication on the instrument is

• 200V
• 0 V
• The instrument follows the variations in voltages and does not give a steady response
• None of the above.

#### 48. Thermocouple instruments can be used for a frequency range

• Up to 100 Hz
• Up to 5000 Hz
• Up to 1 MHz
• 50 MHz and above.

#### 49. The heater wire of thermocouple instrument is made very thin in order to have

• A high value of resistance
• To reduce the skin effect at high frequencies
• To reduce the weight of instrument
• To decrease the over-ranging capacity of the instrument.

• Ammeters
• Wattmeters
• Voltmeters
• Ohmmeters

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