Multiple Choice Questions on Energy Meters for SSC JE Electrical, RRB JE Electrical, ALP/Technician Exam
1. Which of the following is an integrating instrument?
(A) Watt-hour meter ✅
(B) Ammeter
(C) Voltmeter
(D) Wattmeter
Explanation: An integrating instrument accumulates a quantity over time. The watt-hour meter measures energy over time, making it an integrating instrument.
2. The series magnet of a single-phase energy meter consists of a coil of:
(A) Thin wire of few turns
(B) Thick wire of few turns ✅
(C) Thick wire of more turns
(D) Thin wire of more turns
Explanation: A thick wire of few turns ensures a low resistance path and handles high current without excessive heating.
3. In an energy meter, which coil carries the current proportional to supply voltage?
(A) Current coil
(B) Pressure coil ✅
(C) Both pressure and current coil
(D) None of these
Explanation: The pressure coil (also called the voltage coil) is connected across the supply voltage and carries current proportional to voltage.
4. Energy meter measures energy in:
(A) Joules
(B) kW
(C) kWh ✅
(D) W
Explanation: Energy meters measure electrical energy in kilowatt-hours (kWh), which is a unit of energy consumption and also known as commercial unit
5. Copper shading is provided in an energy meter to:
(A) Bring flux exactly in quadrature with applied voltage ✅
(B) Increase the speed of the aluminium disc
(C) Count the rotation
(D) Balance the system from vibration
Explanation: The copper shading band is used to produce a phase shift between fluxes so that the deflecting torque is proportional to power.
6. Holes are drilled on the opposite side of the disc of an induction-type energy meter to:
(A) Prevent creeping ✅
(B) Balance the disc
(C) Dissipate energy due to Eddy current
(D) Increase the deflection torque
Explanation: The holes help eliminate creeping, which is unwanted continuous rotation at no load.
7. Creeping in a single-phase induction-type energy meter may be due to:
(A) Overcompensation for friction
(B) Overvoltages
(C) Vibrations
(D) All of these ✅
Explanation: Various factors, including overcompensation, overvoltage, and mechanical vibrations, can cause creeping in energy meters.
8. Creep in energy meters can be prevented by:
(A) Using a stronger break magnet
(B) Using steel lamination of high permeability
(C) Having two holes on opposite sides of the disc ✅
(D) Using extra turns on the voltage coil
Explanation: Drilling two holes in the disc disrupts uniform rotation at no load, preventing creeping.
9. Energy meter is a:
(A) Recording instrument
(B) Integrating instrument ✅
(C) Indicating instrument
(D) None of these
Explanation: An energy meter records and integrates power consumption over time, making it an integrating instrument.
10. The major cause for creeping in energy meters is:
(A) Overcompensation for friction ✅
(B) Vibrations
(C) Stray magnetic fields
(D) Excessive voltage across the potential coil
Explanation: Overcompensation for friction leads to continuous motion even at no load, causing creeping.
11. Which of the following instruments contains a disc?
(A) Ammeter
(B) Voltmeter
(C) Wattmeter
(D) Energy meter ✅
Explanation: The energy meter has an aluminium disc that rotates due to electromagnetic induction.
12. The loss of charge method can be used to measure:
(A) Resistance of shunt
(B) Resistance of shunt winding
(C) Insulation resistance of cable ✅
(D) Resistance of transformer winding
Explanation: The loss of charge method is used for measuring the insulation resistance of cables and electrical equipment.
13. The household energy meter is:
(A) An indicating instrument
(B) A recording instrument
(C) An integrating instrument ✅
(D) None of these
Explanation: It records and integrates power consumption over time.
14. The pressure coil of an energy meter is:
(A) Purely resistive
(B) Purely inductive✅
(C) Highly resistive
(D) Highly inductive
Explanation: The pressure coil is designed to be highly inductive to maintain 90 degree phase difference.
15. The creeping is observed in:
- (A) Ammeter
- (B) Wattmeter
- (C) Energy meter ✅
- (D) Voltmeter
Explanation: Creeping occurs in energy meters due to excessive voltage, overcompensation for friction, or stray magnetic fields.
16. The disc of a domestic supply energy meter is made of which material?
- (A) Zinc
- (B) Copper
- (C) Aluminium ✅
- (D) Silver
Explanation: Aluminium is lightweight, has good electrical conductivity, and reduces eddy current losses.
17. In a single-phase induction-type energy meter, the deflecting torque is _______ the true power in the circuit.
- (A) Proportional to ✅
- (B) Equal to
- (C) Greater than
- (D) Less than
Explanation: The deflecting torque in an energy meter is proportional to the power being measured.
18. If an induction-type energy meter runs fast, it can be slowed down by:
- (A) Lag adjustment
- (B) Light load adjustment
- (C) Adjusting the position of the braking magnet and making it come closer to the centre of the disc ✅
- (D) Adjusting the position of the braking magnet and making it move away from the centre of the disc
Explanation: Moving the braking magnet closer increases eddy current braking, slowing the meter.
19. Two holes are drilled in the disc of an energy meter to:
- (A) Increase ventilation
- (B) Reduce the weight of the disc
- (C) Eliminate creeping on no load ✅
- (D) Increase deflecting torque
Explanation: Holes prevent continuous unwanted rotation of the disc at no load.
20. Creep occurs in single-phase energy meters when _______ is energized, and it is mainly because of ________.
- (A) Current coil, overcompensation
- (B) Pressure coil, overcompensation ✅
- (C) Pressure coil, under-compensation
- (D) Current coil, under-compensation
Explanation: Overcompensation of friction in the pressure coil causes unwanted rotation, leading to creeping.
21. The energy meter installed at a residence charges the consumer for the use of:
- (A) Apparent power
- (B) True power ✅
- (C) Reactive power
- (D) Product of voltage and current
- Explanation: The meter measures real energy consumption in kWh, which is based on true power (P = VIcosθ).
22. In an energy meter, the braking torque is produced to:
- (A) Safeguard it against creep
- (B) Break the instrument
- (C) Bring the energy meter to a standstill
- (D) Maintain steady speed and equal to driving torque ✅
Explanation: The braking torque, provided by a permanent magnet, ensures stable operation of the meter.
23. Creeping in a single-phase induction-type energy meter may be due to:
- (A) Overvoltage
- (B) Vibrations
- (C) Overcompensation for friction
- (D) All of the given options ✅
Explanation: Several factors contribute to creeping, including overvoltage, vibrations, and overcompensation.
24. A single-phase 230V energy meter has a constant load of 5 A passing through it for 6 hours at unity power factor. If the meter disc makes 2070 revolutions during this period, what is the meter constant in revolutions per unit?
- (A) 100 rev/unit
- (B) 200 rev/unit
- (C) 300 rev/unit ✅
- (D) 400 rev/unit
Explanation: Energy consumed = 230V × 5A × 6 hours = 6.9 kWh. Meter constant = 2070 rev / 6.9 kWh = 300 rev/unit.
25. An energy meter is designed to make 100 revolutions for one unit of energy. Calculate the number of revolutions made by it when connected to a load carrying 50 A at 230V and 0.6 power factor for one hour.
- (A) 575 revolutions
- (B) 1150 revolutions ✅
- (C) 920 revolutions
- (D) 690 revolutions
Explanation: Energy consumed = 50 × 230 × 0.6 × 1 = 6.9 kWh. Total revolutions = 6.9 × 100 = 1150.
26. An energy meter is designed to make 100 revolutions for one unit of energy. The number of revolutions when connected to a load of 40A, at 230V and 0.95 power factor lagging for an hour is:
- (A) 657
- (B) 874 ✅
- (C) 362
- (D) 530
Explanation: Energy consumed = 40 × 230 × 0.95 × 1 = 8.74 kWh. Total revolutions = 8.74 × 100 = 874.
27. A single-phase energy meter has a constant of 1200 revolutions/kWh. When a load of 200 W is connected, the disc rotates at 4.2 revolutions per minute. If the load is on for 10 hours, the meter records an excess of:
- (A) 0.1 kWh
- (B) 0.2 kWh ✅
- (C) 1.0 kWh
- (D) 2.0 kWh
Explanation: Expected revolutions in 10 hours = 200 × 10 × 1200 / 1000 = 2400. Excess revolutions recorded = 240, leading to an excess of 0.2 kWh.
28. The meter constant of a single-phase energy meter is 500 rev/kWh. The meter takes 86 seconds to make 50 revolutions while measuring a full load of 4.4 kW. The percentage error in the meter is:
- (A) -2.43%
- (B) 2.43% ✅
- (C) -4.86%
- (D) 4.86%
Explanation: Actual kWh recorded = 50 × (1 / 500) = 0.1 kWh. Expected = 4.4 × (86 / 3600) = 0.105 kWh. Error = ((0.1 - 0.105) / 0.105) × 100 = 2.43%.
29. In an induction-type energy meter, everything else remaining the same, if the radial distance of the brake magnet poles from the spindle is decreased by 10%, the rotational speed of the disc will _______ approximately.
- (A) Increase by 23.5%
- (B) Decrease by 10.6%
- (C) Decrease by 19.4% ✅
- (D) Increase by 11%
Explanation: Braking torque is inversely proportional to the square of the radial distance, leading to a decrease in speed.
30. The voltage coil of a single-phase house energy meter:
- (A) Is highly inductive
- (B) Is highly resistive ✅
- (C) Is highly capacitive
- (D) Has a phase angle equal to the load power factor angle
Explanation: The voltage coil is designed to be highly resistive to minimize phase angle errors.