21. The energy meter installed at the residence charges the consumer for the use of

- Apparent power
- True power
- Reactive power
- Product of voltage and current

22. In energy meter, the braking torque is produced to

- Safeguard it against creep
- Break the instrument
- Bring energy meter to a standstill
- Maintain steady speed and equal to driving torque

23. Creeping in a single-phase induction type energy meter may be due to?

- Overvoltage
- Vibrations
- Overcompensation for friction
- All of the given options

24. A single-phase 230V energy meter has a constant load of 5 A passing through it for 6 hours was at unity power factor. If the meter disc makes 2070 revolutions during this period, what is the meter constant in revolutions per unit?

- 100 rev/unit
- 200 rev/unit
- 300 rev/unit
- 400 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 load carrying 50 A at 230V and 0.6 power factor an hour.

- 575 revolutions
- 1150 revolutions
- 920 revolutions
- 690 revolutions

26. An energy meter is designed to make 100 revolutions for one unit of energy. The number of revolution when connected to a load of 40A, at 230V and 0.95 power factor lagging for an hour is

- 657
- 874
- 362
- 530

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

- 0.1 kWh
- 0.2 kWh
- 1.0 kWh
- 2.0 kWh

28. The meter constant of a single-phase energy meter is 500 rev/kWh. The metre takes 86 seconds to make 50 revolutions while measuring a full load of 4.4 kW. The percentage error in the meter is

- -2.43%
- 2.43%
- -4.86%
- 4.86%

29. In an induction type energy meter, everything else remaining 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.

- Increase by 23.5%
- Decrease by 10.6%
- Decrease by 19.4%
- Increase by 11%

30. The voltage coil of a single phase house energy meter

- is highly inductive
- is highly resistive
- is highly capacitive
- has a phase angle equal to load power factor angle