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Electronics and Communication Engineering - Measurements and Instrumentation

Exercise : Measurements and Instrumentation - Section 3
26.
The emf of a Weston cell is 1.286 V.
True
False
Answer: Option
Explanation:

It is 1.01859.

27.
The power factor of a single phase load can be calculated if instruments available are
one voltmeter, one ammeter
two ammeters
two voltmeters
one voltmeter, one ammeter and one wattmeter
Answer: Option
Explanation:

, we need to, measure active power, voltage and current.

28.
A variable reluctance type tachometer has 150 teeth on rotor. The counter records 13500 pulse/sec. The rotational speed is
4800 RPM
5400 RPM
6000 RPM
7200 RPM
Answer: Option
Explanation:

.

29.
The current through the coil of an electromagnet is doubled. The magnetic field around the coil
is halved
is doubled
becomes four times
remains the same
Answer: Option
Explanation:

B ∝ H.

30.
In a moving iron voltmeter the coil has a resistance of 20 Ω and an inductance of 0.3 H. The swamping resistance in 2000 Ω. To ensure correct reading with dc as well as 50 Hz ac, the value of capacitor to be connected in parallel with swamping resistance should be
0.0125 μF
0.0311 μF
0.0521 μF
0.0622 μF
Answer: Option
Explanation:

C = 0.41 L/R2

or C = (0.41 x 0.3)/(2000)2 = 0.0311 x 10-6 F.

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