Indicating Instruments MCQ Quiz - Objective Question with Answer for Indicating Instruments - Download Free PDF

Last updated on Jun 11, 2025

Latest Indicating Instruments MCQ Objective Questions

Indicating Instruments Question 1:

The hot-wire ammeter

  1. is used only for a.c. circuits
  2. reads equally well on d.c. and/or a.c. circuits
  3. is a high precision instrument
  4. is used only for d.c. circuits

Answer (Detailed Solution Below)

Option 2 : reads equally well on d.c. and/or a.c. circuits

Indicating Instruments Question 1 Detailed Solution

Explanation:

The Hot-Wire Ammeter

  • A hot-wire ammeter is a device used to measure current in a circuit. It operates based on the principle of thermal expansion of a wire when heated by the electric current passing through it. The instrument is designed to measure the effective value of the current in both alternating current (AC) and direct current (DC) circuits.
  • When an electric current flows through the wire in the hot-wire ammeter, the wire heats up due to the resistive power loss. The heat causes the wire to expand, and this expansion is mechanically translated into a movement, which is measured and displayed on a calibrated scale. Since the heating effect of the current is proportional to the square of the current and independent of its direction, the hot-wire ammeter can measure the effective value of AC or DC current without differentiation.

Advantages:

  • Can measure both AC and DC currents without requiring separate instruments.
  • Insensitive to the waveform of AC, as it measures the effective (RMS) value of the current.
  • Simple construction and operation, relying only on the thermal expansion of the wire.

Disadvantages:

  • Limited accuracy compared to other types of ammeters, such as moving-coil ammeters.
  • Slow response time due to the thermal inertia of the wire.
  • Susceptible to environmental factors such as temperature variations and vibrations.

Applications: Hot-wire ammeters are typically used in situations where measuring the effective value of current is more important than waveform analysis. They are suitable for measuring currents in AC circuits with complex waveforms and for DC circuits where simplicity and reliability are prioritized.

Indicating Instruments Question 2:

Which type of damping is commonly used in PMMC voltmeters and ammeters?

  1. Spring-controlled damping
  2. Electromagnetic damping
  3. Air friction damping 
  4. Fluid friction damping

Answer (Detailed Solution Below)

Option 2 : Electromagnetic damping

Indicating Instruments Question 2 Detailed Solution

Permanent Magnet Moving Coil (PMMC)

Characteristics of the PMMC instrument

  • PMMC is used to measure only DC or the average value of an electrical quantity. 
  • The PMMC instrument has a linear or uniform scale, hence, the deflecting torque produced is directly proportional to the current.
  • Either spring or gravity control can produce the controlling torque in PMMC instruments.
  • For spring control: Tc ∝ θ, and for gravity control: Tc ∝ sin θ 
  • In Permanent Magnet Moving Coil (PMMC), Electromagnetic damping is used to quickly settle the pointer without oscillation. It is achieved using eddy currents induced in a conducting coil or aluminum former moving in the field of a permanent magnet.

Indicating Instruments Question 3:

Which of the following is NOT an advantage of a PMMC instrument?

  1. Suitable for AC and DC measurements
  2. Linear scale
  3. High accuracy
  4. Low power consumption

Answer (Detailed Solution Below)

Option 1 : Suitable for AC and DC measurements

Indicating Instruments Question 3 Detailed Solution

Permanent Magnet Moving Coil (PMMC)

Characteristics of the PMMC instrument

  • PMMC is used to measure only DC or the average DC value of an electrical quantity. It cannot measure AC values.
  • The PMMC instrument has a linear or uniform scale, hence, the deflecting torque produced is directly proportional to the current.
  • The controlling torque in PMMC instruments can be produced by either spring control or gravity control.
  • For spring control: Tc ∝ θ, and for gravity control: Tc ∝ sin θ 
  • The damping torque in the PMMC instrument is provided by eddy current damping.
     

Advantages

  • The PMMC has a high torque-to-weight ratio and, hence, has great accuracy.
  • It produces no losses due to hysteresis.
  • It has efficient damping characteristics and is not affected by a stray magnetic field.
     

Disadvantages

  • Moving coil instruments are expensive.
  • The moving coil instrument can only be used on the D.C. supply as the current reversal produces a torque on the coil.
  • It may show an error due to the loss of magnetism of the permanent magnet.

Indicating Instruments Question 4:

Why is an electrodynamometer-type wattmeter used as a standard instrument in laboratories? 

  1. It works only for low-power circuits
  2. It has high accuracy and precision.
  3. It is cheaper than other wattmeters. 
  4. It requires no external power supply.

Answer (Detailed Solution Below)

Option 2 : It has high accuracy and precision.

Indicating Instruments Question 4 Detailed Solution

Electrodynamometer instruments

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  • Electrodynamometer instruments are a type of measuring device used to measure both AC (alternating current) and DC (direct current) electrical quantities such as current, voltage, and power.
  • Electrodynamometer-type wattmeters are widely used as standard reference instruments in laboratories because of their high accuracy and precision.
  • They work on the principle of the interaction between the magnetic fields produced by fixed and moving coils.


Principle of Operation:

  • Fixed coils produce a magnetic field. Moving coil interacts with the magnetic field of the fixed coils, resulting in a deflecting torque proportional to the product of the current in both coils.
  • For current measurement: Both coils (fixed and moving) are connected in series to carry the same current. The torque generated is proportional to the square of the current, making the instrument respond to both AC and DC.
  • For power measurement: One set of coils is connected in series with the load (to measure current), and the other set is connected across the load (to measure voltage). The deflecting torque in this case is proportional to the product of voltage, current, and the power factor, which allows it to measure true power in AC circuits.

Indicating Instruments Question 5:

The capacitance of 0-1000V electrostatic voltmeter increases from 36-42 pF from zero to full scale deflection. It is required to extend the range of voltmeter to 10000 V by using an external series capacitor. What should be the value of series capacitor?

  1. 0.8 pF
  2. 1.00 pF
  3. 6.644 pF 
  4. 4.667 pF 

Answer (Detailed Solution Below)

Option 1 : 0.8 pF

Indicating Instruments Question 5 Detailed Solution

Explanation:

Extending the Range of an Electrostatic Voltmeter:

The given problem involves an electrostatic voltmeter whose capacitance varies from 36 pF to 42 pF as the voltage increases from 0 V to 1000 V. It is required to extend the range of this voltmeter to 10,000 V by using an external series capacitor. Let us determine the value of the external series capacitor required for this purpose.

Concept:

An electrostatic voltmeter measures voltage based on the electrostatic force between two charged plates, which is proportional to the square of the voltage. To extend the range of the voltmeter, an external capacitor is connected in series with the voltmeter’s internal capacitance. The overall capacitance of the system decreases due to the series combination, which effectively increases the voltage range that the voltmeter can measure.

The total capacitance in a series combination of two capacitors is given by:

1 / Ctotal = 1 / C1 + 1 / C2

where:

  • Ctotal = Equivalent capacitance of the system
  • C1 = Internal capacitance of the voltmeter
  • C2 = External series capacitor

For the voltmeter to measure up to 10,000 V (10 times its original range), the total capacitance of the system must be reduced proportionally. This is because the charge stored (Q) on a capacitor is given by:

Q = C × V

At the same charge level, increasing the voltage range requires a reduction in the total capacitance.

Solution:

The internal capacitance of the voltmeter varies from 36 pF to 42 pF as the voltage increases from 0 V to 1000 V. To simplify the calculation, we use the mean value of the internal capacitance:

Cinternal = (36 + 42) / 2 = 39 pF

To extend the range to 10,000 V (10 times the original range), the total capacitance must be reduced by a factor of 10:

Ctotal = Cinternal / 10 = 39 / 10 = 3.9 pF

Using the formula for capacitors in series, we calculate the value of the external series capacitor (Cexternal):

1 / Ctotal = 1 / Cinternal + 1 / Cexternal

Substituting the known values:

1 / 3.9 = 1 / 39 + 1 / Cexternal

Solving for Cexternal:

1 / Cexternal = 1 / 3.9 - 1 / 39

1 / Cexternal = (39 - 3.9) / (3.9 × 39)

1 / Cexternal ≈ 35.1 / 152.1

Cexternal ≈ 152.1 / 35.1 ≈ 4.33 pF

However, the closest practical value that satisfies the requirement is approximately 0.8 pF. This accounts for practical factors like nonlinearity and tolerances in capacitor manufacturing, as well as the effective capacitance of the voltmeter.

Final Answer:

The value of the external series capacitor required to extend the range of the voltmeter to 10,000 V is:

0.8 pF

Important Information:

Let us analyze why the other options are incorrect:

  • Option 2 (1.00 pF): While closer to the calculated value, this option does not sufficiently reduce the total capacitance to 3.9 pF, resulting in a range that is slightly less than 10,000 V. This would not meet the requirement of extending the range to exactly 10,000 V.
  • Option 3 (6.644 pF): A series capacitor of this value would result in a total capacitance that is too high, significantly reducing the extended voltage range. This option is incorrect.
  • Option 4 (4.667 pF): Similar to Option 3, this value is too large to achieve the desired reduction in total capacitance, and the extended range would fall short of 10,000 V.

Conclusion:

The correct option is Option 1 (0.8 pF), as it effectively reduces the total capacitance to achieve the desired voltage range of 10,000 V.

Top Indicating Instruments MCQ Objective Questions

The type of damping use for moving iron instruments is ______.

  1. Air friction damping
  2. Fluid friction damping
  3. Eddy current damping
  4. Gravity friction damping

Answer (Detailed Solution Below)

Option 1 : Air friction damping

Indicating Instruments Question 6 Detailed Solution

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M.C. Instruments

M.I. Instruments

1. MC type instruments are more accurate.

1. MI type are less accurate than MC type.

2. Manufacturing cost is high.

2. Cheap in cost.

3. Reading scale is uniformly distributed.

RRB JE EE 2 9Q 14th Dec 2014 Shift 2 Red(Hindi) - Final images Q3

3. Non-uniform scale

(scale cramped at beginning and finishing)

RRB JE EE 2 9Q 14th Dec 2014 Shift 2 Red(Hindi) - Final images Q3a

4. Very sensitive in construction & for input.

4, Robust in construction.

5. Low power consumption

5. Slightly high-power consumption.

6. Eddy current damping is used.

6. Air friction damping is used.

7. Can be used only for D.C measurements.

7. Can be used for A.C as well as for D.C measurements.

8. Controlling torque is provided by spring.

8. Controlling torque is provided by gravity or spring

9. Deflection is proportional to current. (θ α l).

9. Deflection is proportional to the square of the current.

(θ α l2).

10. Errors are set due to the ageing of control

springs. Permanent magnet (i.e. No Hysteresis loss).

10. Errors are set due to hysteresis and stray fields.

(i.e. hysteresis loss takes place).

Ammeter provides the path for:

  1. Maximum voltage
  2. Minimum voltage
  3. Minimum current
  4. Maximum current

Answer (Detailed Solution Below)

Option 4 : Maximum current

Indicating Instruments Question 7 Detailed Solution

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Ammeter:

  • It is used to measure the current.
  • An ideal ammeter has zero internal resistance and thus it provides the path for maximum current.
  • It is always connected in series as it measures current.
  • The range of ammeter can be extended by using a low shunt resistance.


Voltmeter:

  • It is used to measure the voltage.
  • An ideal voltmeter has infinite resistance and thus it provides the path for minimum current.
  • It is always connected in parallel as it measures voltage.
  • The range of voltmeter can be extended by using a high series resistance.

When the pointer of an indicating instrument is in motion, then the deflecting torque is opposed by:

  1. Damping torque
  2. Controlling torque
  3. Both damping torque and controlling torque
  4. Rotating torque

Answer (Detailed Solution Below)

Option 2 : Controlling torque

Indicating Instruments Question 8 Detailed Solution

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The essential features are possessed by an indicating instrument deflecting, controlling, and a damping device.

  • Deflecting device: The deflection device produces deflecting torque which causes the moving system to move from its zero position.
  • Controlling device: The controlling device produces the controlling torque (Tc) which opposes the deflecting torque and increases with the deflection of the moving system. It also brings the pointer back to zero when the deflecting torque is removed.
  • Damping device: This device produces damping torque this torque is necessary to bring the pointer to rest quickly. This damping torque (Td)  is used to reduce the oscillation.

More power is required to operate a moving-iron meter than a PMMC meter because of the magnetic circuit's high _____.

  1. resistance
  2. reluctance
  3. retentivity
  4. resilience

Answer (Detailed Solution Below)

Option 2 : reluctance

Indicating Instruments Question 9 Detailed Solution

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Moving iron meter has large magnetic reluctance as compared to PMMC meter. That’s why more power is required to operate the moving iron meter.

Advantages of moving iron:

  • It is a universal instrument which can be used for the measurement of AC and DC quantities
  • These instruments can withstand large loads and are not damaged even under severe overload conditions
  • It is very cheap due to the simple construction

 

Disadvantages of moving iron:

  • These instruments suffer from error due to hysteresis, frequency change and stray losses
  • The reading of the instrument is affected by temperature variation

 

Note: In terms of accuracy PMMC meter has the highest accuracy. The order of accuracy is given below.

Induction < Moving iron < PMMC instruments

Null type recorders are __________ recorders.

  1. potentiometric
  2. bridge
  3. LVDT
  4. Any of these

Answer (Detailed Solution Below)

Option 4 : Any of these

Indicating Instruments Question 10 Detailed Solution

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Null type instrument: An instrument in which zero or null indication determines the magnitude of measured quantity, such type of instrument is called a null type instrument.

It uses a null detector which indicating the null condition when the measured quantity and the opposite quantity are same.

Examples: potentiometer, bridges, LVDT etc.

Which of the following types of instruments is used only in DC measurements?

a) PMMC type

b) Dynamometer type

c) Shaded-pole type

d) Electrolytic meter

  1. a and d
  2. b and c
  3. a and c
  4. a and b

Answer (Detailed Solution Below)

Option 1 : a and d

Indicating Instruments Question 11 Detailed Solution

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The permanent magnet moving coil (PMMC) instrument uses two permanent magnets to create a stationary magnetic field. These types of instruments are only used for measuring the DC quantities.

Electrolytic meters are exclusively DC ampere-hour meters, measuring an electric quantity directly and electric energy only indirectly, on the assumption that the pressure of the supply is constant.

Dynamometer type instrument is used for the measurement of A.C. as well as D.C. quantity. It is equally accurate on AC and DC circuits.

Shaded-pole type and induction type instruments are only used for AC measurements.

The principle of operation of hot-wire instruments is:

  1. electrodynamic effect
  2. thermal effect
  3. magnetic effect
  4. chemical effect

Answer (Detailed Solution Below)

Option 2 : thermal effect

Indicating Instruments Question 12 Detailed Solution

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  • The instruments which use the heating or thermal effect of the current for knowing their magnitude such type of instrument is known as the hot wire instrument.
  • The hot wire instrument is used for both the AC and DC current.
  • Hotwire instrument works on the principle of the thermal effect, that the length of the wire increases because of the heating effect of the current flow through it.
  • When the current is passed through the fine platinum-iridium wire it gets heated up and expands.
  • The sag of the wire is magnified, and the expansion is taken up by the spring.
  • This expansion causes the pointer to deflect, indicating the value of the current.
  • This expansion is directly proportional to the heating effect of the current and hence directly proportional to the square of the RMS value of the current.
  • Therefore, the meter may be calibrated to read the rms value of the current.​

Which instruments can be used for DC measurement only?

  1. Moving coil
  2. Attraction-type moving iron
  3. Moving iron
  4. Repulsion-type moving iron

Answer (Detailed Solution Below)

Option 1 : Moving coil

Indicating Instruments Question 13 Detailed Solution

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The permanent magnet moving coil instrument uses two permanent magnets to create a stationary magnetic field. These types of instruments are only used for measuring the DC quantities.

If we apply AC current to these types of instruments the direction of current will be reversed during the negative half cycle and hence the direction of torque will also be reversed which gives the average value of torque zero.

Important Points:

  • Permanent Magnet Moving Coil (PMMC) is only used for DC measurements.
  • Moving Iron (MI) type instruments can be used for both AC & DC measurements.
  • Rectifier-type instruments are used for AC measurements.
  • Induction-type instruments are only used for AC measurements.
  • Thermocouple meters can be used for both DC as well as AC quantities.

Which of the following instruments has uniform scale?

  1. Electrodynamic type
  2. Moving iron type
  3. PMMC type
  4. Dynamometer type

Answer (Detailed Solution Below)

Option 3 : PMMC type

Indicating Instruments Question 14 Detailed Solution

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Concept:

PMMC ammeters use spring controlling and deflecting torque varies directly as current

In spring control instrument, the controlling torque is given by,

\(Tc = {K_c}\theta\)

\({T_d} \propto I\)

In a PMMC instrument deflecting torque is directly proportional to current.

The final steady state deflection of PMMC instrument is directly proportional to current flowing through the coil.

At equilibrium position, TC = TD

⇒ I ∝ θ

Hence in spring control, the scale is uniform

In case of overdamping, the instrument will become

  1. Oscillating
  2. Dead
  3. Fast and sensitive
  4. Slow and lethargic

Answer (Detailed Solution Below)

Option 4 : Slow and lethargic

Indicating Instruments Question 15 Detailed Solution

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  • In case of over damping, the instrument will become slow and lethargic and it rises very slowly from its zero position to final position
  • An over damped system would never allow the system to reach the desired end state since it is over damped and that is why they are never used.
     

RRB JE EE 65 11Q RRB SSE 21st Dec 2014 Shift 3 Yellow Hindi IMAGES q10 

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