Measurements and Instrumentation

466

In 3 phase power measurement by two wattmeter method, the reading of one wattmeter is zero. The power factor of load is

A. 1
B. 0.5
C. 0
D. 0.8

467

The coil of a moving iron instrument has a resistance of 500 Ω and an inductance of 1 H. It reads 250 V when a 250 V dc is applied. If series resistance is 2000 Ω, its reading when fed by 250 V, 50 Hz ac will be

A. 260 V
B. 252 V
C. 250 V
D. 248 V

468

An ammeter of 0-25 A range has a guaranteed accuracy of 1% of full scale reading. The current measured is 5 A. The limiting error is

A. 2%
B. 2.5%
C. 4%
D. 5%

469

To increase Q factor of a coil, the wire should be

A. long
B. thin
C. thick
D. long and thin