Wattmeter MCQ

31. In an electrodynamometer type wattmeter if the voltage and current measured are given by v=100 sin314t and i=10 sin(314t –60°) respectively, the reading (in watts) will be

  1. 1000
  2. 500
  3. 250
  4. 433
Answer
Answer. c

32. One single-phase wattmeter operating on 230V and 5A for 5 hours makes 1940 revolutions. Meter constant in revolution is 400. The power factor of the load will be

  1. 1
  2. 0.8
  3. 0.7
  4. 0.6
Answer
Answer. b

33. In a single-phase induction type wattmeter, a meter can be reversed by

  1. Reversing either the potential coil terminal or current coil terminals
  2. Reversing connections of both current and potential coil circuits
  3. Reversing the supply terminals
  4. Reversing the load terminals
Answer
Answer. a

34. In an electrodynamometer type wattmeter

  1. The current coil is made fixed
  2. The pressure coil is fixed
  3. Both the coil are fixed
  4. Both the coils are movable
Answer
Answer. a

35. An automatic power factor controller can not achieve

  1. Voltage control
  2. kVAR control
  3. kW control
  4. pf control
Answer
Answer. c

36. A dynamometer type wattmeter can be used on

  1. d.c. only
  2. a.c. only
  3. rectified a.c. only
  4. a.c. as well as d.c.
Answer
Answer. d

37. In phantom loading arrangement, energy consumption in the calibration test of wattmeter is reduced because of

  1. The separate application of voltage supply across current coil
  2. No common point between the two coils
  3. The reduced loss in current coil and pressure coil
  4. The absence of load in the test set
Answer
Answer. d

38. In a balanced 3-phase system, the current coil of a wattmeter is inserted in line 1 and the potential coil across 2 and 3.If the wattmeter reads 100W, the reactive power drawn by the 3-phase load is

  1. 173.2 VAR
  2. 50 VAR
  3. 100 VAR
  4. 141.4 VAR
Answer
Answer. a

39. In a balanced 3-phase circuit, the line current is 12A. When the power is measured by two wattmeter method, one meter reads 11 kW while the other reads zero. Power factor of the load is

  1. 0
  2. 0.5
  3. 0.866
  4. 1.0
Answer
Answer. b

40. The pressure coil of a wattmeter consists of

  1. More number of turns of fine wire
  2. Less number of turns of fine wire
  3. Less number of turns of thick wire
  4. More number of turns of thick wire
Answer
Answer. a
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