In 3 phase power measurement by two wattmeter method, the reading of one wattmet

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Question
In 3 phase power measurement by two wattmeter method, the reading of one wattmeter is zero. The power factor of load is
Options
A. 1
B. 0.5
C. 0
D. 0.8

Correct Answer

0.5

Explanation

When p.f. = 0.5, 0 = 60� and one of the wattmeters reads zero.

Measurements and Instrumentation problems

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2. Which of the following is true about an impulse voltage?
Options
A. It is a unidirectional voltage
B. Chopped impulse flashover does not occur
C. Time taken to rise is equal to time taken to fall
D. RMS value is always less than 50% of average value

4. A moving iron instrument gives correct reading when used at
Options
A. low frequencies
B. high frequencies
C. only one frequency
D. all frequencies upto a certain value

5. A full wave rectifier type meter is used to measure the wave shape shown in figure. The voltmeter is calibrated to read rms value of sine wave. The reading of voltmeter will be
Options
A.
B.
C. 100 V
D. 111 V

6. Which power amplifier can deliver maximum load power?
Options
A. Class A
B. Class AB
C. Class B
D. Class C

7. A half wave diode circuit using ideal diode has an input voltage 20 sin ?t volts. Then average and rms values of output voltage are
Options
A. and 10 V
B. and 10 V
C. and 5 V
D. and 5 V

8. In figure v₁ = 8 V and v₂ = 8 V. Which diode will conduct?
Options
A. D₁ only
B. D₂ only
C. Both D₁ and D₂
D. Neither D₁ nor D₂

10. Which of the following oscillators is suitable for frequencies in the range of mega hertz?
Options
A. RC phase shift
B. Wien bridge
C. Hartley
D. Both (a) and (c)

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