Wattmeter MCQ

41. According to Blondel’s theorem, if a network is supplied using ‘n’ conductors’ the total power is the _________ of the reading of n wattmeters so arranged that a current coil of each wattmeter is in each line and the corresponding pressure coil is connected between that line and a common point.

1. Sum
2. Product
3. Sum of products of two wattmeter’s reading taken together
4. Difference

42. The power of an n-phase circuit can be measured by using a minimum of

1. n elements
2. 2n wattmeter elements
3. (n-1) wattmeter element
4. (n+1) wattmeter element

43. In a balanced 3-phase 400V circuit, the line current is 115.5 A when the power is measured by two wattmeter method, one meter reads 40kW and the other zero. What is the power factor of the load?

1. 1
2. 0.5
3. 0.6
4. 0.8

44. Wattmeter is an instrument which measures

1. Instantaneous power
2. Average power
3. Apparent power
4. Reactive power

45. In a 3-phase, 3-wire unbalanced load, power can not be measured by two wattmeters

1. TRUE
2. FALSE
3. Can not be said
4. None of these

46. Two wattmeter method for measuring power factor is used for

1. balanced load only
2. balanced and unbalanced loads
3. unbalanced load only
4. star connected balanced load only

47. The pressure col of a dynamometer type wattmeter is

1. Highly inductive
2. Highly resistive
3. Purely resistive
4. Purely inductive

48. The pressure coil of a wattmeter should be on the supply side of the current coil when

1. supply voltage is low
2. supply voltage is high
3. load impedance is low
4. load impedance is high

49. A compensated wattmeter has its reading corrected for error due to the

1. frequency
2. friction
3. power consuned in current coil
4. power consumed in potential coil

50. In two wattmeter method of measuring 3-phase power, power factor is 0.5. Then, one of the wattmeters will read

1. $\frac{W}{2}$
2. zero
3. $\sqrt{2}W$
4. $\frac{W}{\sqrt{3}}$