21. Calculate the percentage error for a wattmeter which is so connected that the current coil is on the load side. The wattmeter has a current coil of 0.03 ohm resistance and a pressure coil of 6000 ohm resistance. It is also known that the load takes 20A at a voltage of 220V and 0.6 power factor.
- 0.45 %
- 45 %
- 5.5 %
- 6.5 %
22. In a single phase dynamometer wattmeter, the instantaneous torque has a component of power which varies as
- Twice
- Half
- Four times
- Three times
23. Laboratory wattmeters are
- Induction type
- Moving iron type
- Electrostatic type
- Electro-dynamometer type
24. For power measurement of three-phase circuit by two wattmeter method, when the value of power factor is less than 0.5 lagging
- One of the wattmeter’s will read zero
- Both give the same readings
- One of the wattmeter connections will have to be reversed
- Pressure coil of the wattmeter will become ineffective
25. Power consumed by a balanced 3-phase, 3-wire load is measured by two wattmeter method. The first wattmeter reads twice that of the second. Then what will be the load impedance angle in radian?
- π/6
- π/3
- π/2
- π/4
26. A compensated wattmeter has its reading corrected for error due to
- Frequency
- Friction
- Power consumed in current coil
- Power consumed in pressure coil
27. If a dynamometer wattmeter is connected in an AC circuit, the power indicated by the wattmeter will be
- Volt-ampere product
- Average power
- Peak power
- Instantaneous power
28. How many coils are there in a wattmeter?
- 2
- 3
- 4
- 1
29. Which of the following provide deflecting force for voltmeters only?
- Electromagnetic effect
- Electrodynamic effect
- Magnetic effect
- Electrostatic effect
30. In the measurement of 3 phase power by two wattmeter method, for an unbalanced load, the power factor of the load is
- $\cos [\tan^{-1}{\frac{\sqrt{3}(W_2-W_1)}{W_2+W_1}}]$
- $\cos [\tan^{-1}{\frac{(W_2-W_1)}{W_2+W_1}}]$
- $\cos (W_2-W_1)$
- None of these