Electronics and Communication Engineering - Measurements and Instrumentation

41. 

Which of the following measurements using a dc potentiometer do not require standardisation of potentiometer?

A. Measurement of unknown voltage
B. Measurement of resistance
C. Measurement of unknown current
D. Calibration of voltmeter

Answer: Option B

Explanation:

Unknown resistance is compared with a standard resistance. Therefore standardisation of potentiometer is not necessary.


42. 

Which of the following statement is correct for two wattmeters method of power measurement in 3 phase circuit?

A. Power can be measured by this method only for star connected loads
B. When two wattmeters have equal readings power factor is 0.5.
C. When power factor is 1, one of the wattmeters readings is zero
D. When the two wattmeter read equal and opposite, p.f. is zero.

Answer: Option D

Explanation:

When p.f. is zero, active power is zero and the two redaings are equal and opposite.


43. 

In a thermocouple temperature transducer, the output voltage is usually measured by

A. high resistance ammeter
B. high resistance voltmeter
C. high resistance milli-voltmeter
D. none of the above

Answer: Option C

Explanation:

The output voltage is very small. So we need a milli voltmeter.


44. 

A moving iron instrument gives correct reading when used at

A. low frequencies
B. high frequencies
C. only one frequency
D. all frequencies upto a certain value

Answer: Option C

Explanation:

If frequency changes reactance of coil changes and reading is affected.


45. 

Induction wattmeter can be used in

A. ac circuit only
B. dc circuit only
C. both ac and dc circuit
D. ac 3 phase only

Answer: Option A

Explanation:

Induction effect occurs with ac only.